pavlov experiment of classical conditioning

Classical Conditioning: How It Works With Examples

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

On This Page:

Classical conditioning (also known as Pavlovian or respondent conditioning) is learning through association and was discovered by Pavlov , a Russian physiologist. In simple terms, two stimuli are linked together to produce a new learned response in a person or animal.

John B. Watson proposed that the process of classical conditioning (based on Pavlov’s observations) was able to explain all aspects of human psychology.

If you pair a neutral stimulus (NS) with an unconditioned stimulus (US) that already triggers an unconditioned response (UR) that neutral stimulus will become a conditioned stimulus (CS), triggering a conditioned response (CR) similar to the original unconditioned response.

Everything from speech to emotional responses was simply patterns of stimulus and response. Watson completely denied the existence of the mind or consciousness. Watson believed that all individual differences in behavior were due to different learning experiences.

Watson (1924, p. 104) famously said:

Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select – doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and the race of his ancestors.

How Classical Conditioning Works

There are three stages of classical conditioning. At each stage, the stimuli and responses are given special scientific terms:

Stage 1: Before Conditioning:

In this stage, the unconditioned stimulus (UCS) produces an unconditioned response (UCR) in an organism.

In basic terms, this means that a stimulus in the environment has produced a behavior/response that is unlearned (i.e., unconditioned) and, therefore, is a natural response that has not been taught. In this respect, no new behavior has been learned yet.

For example, a stomach virus (UCS) would produce a response of nausea (UCR). In another example, a perfume (UCS) could create a response of happiness or desire (UCR).

This stage also involves another stimulus that has no effect on a person and is called the neutral stimulus (NS). The NS could be a person, object, place, etc.

The neutral stimulus in classical conditioning does not produce a response until it is paired with the unconditioned stimulus.

Stage 2: During Conditioning:

During this stage, a stimulus which produces no response (i.e., neutral) is associated with the unconditioned stimulus, at which point it now becomes known as the conditioned stimulus (CS).

For example, a stomach virus (UCS) might be associated with eating a certain food such as chocolate (CS). Also, perfume (UCS) might be associated with a specific person (CS).

For classical conditioning to be effective, the conditioned stimulus should occur before the unconditioned stimulus, rather than after it, or during the same time. Thus, the conditioned stimulus acts as a type of signal or cue for the unconditioned stimulus.

In some cases, conditioning may take place if the NS occurs after the UCS (backward conditioning), but this normally disappears quite quickly. The most important aspect of the conditioning stimulus is the it helps the organism predict the coming of the unconditional stimulus.

Often during this stage, the UCS must be associated with the CS on a number of occasions, or trials, for learning to take place.

However, one trial learning can happen on certain occasions when it is not necessary for an association to be strengthened over time (such as being sick after food poisoning or drinking too much alcohol).

Stage 3: After Conditioning:

The conditioned stimulus (CS) has been associated with the unconditioned stimulus (UCS) to create a new conditioned response (CR).

For example, a person (CS) who has been associated with nice perfume (UCS) is now found attractive (CR). Also, chocolate (CS) which was eaten before a person was sick with a virus (UCS) now produces a response of nausea (CR).

Classical Conditioning Examples

Pavlov’s dogs.

The most famous example of classical conditioning was Ivan Pavlov’s experiment with dogs , who salivated in response to a bell tone. Pavlov showed that when a bell was sounded each time the dog was fed, the dog learned to associate the sound with the presentation of the food.

He first presented the dogs with the sound of a bell; they did not salivate so this was a neutral stimulus. Then he presented them with food, they salivated. The food was an unconditioned stimulus, and salivation was an unconditioned (innate) response.

He then repeatedly presented the dogs with the sound of the bell first and then the food (pairing) after a few repetitions, the dogs salivated when they heard the sound of the bell. The bell had become the conditioned stimulus and salivation had become the conditioned response.

Fear Response

Watson & Rayner (1920) were the first psychologists to apply the principles of classical conditioning to human behavior by looking at how this learning process may explain the development of phobias.

They did this in what is now considered to be one of the most ethically dubious experiments ever conducted – the case of Little Albert . Albert B.’s mother was a wet nurse in a children’s hospital. Albert was described as ‘healthy from birth’ and ‘on the whole stolid and unemotional’.

When he was about nine months old, his reactions to various stimuli (including a white rat, burning newspapers, and a hammer striking a four-foot steel bar just behind his head) were tested.

Only the last of these frightened him, so this was designated the unconditioned stimulus (UCS) and fear the unconditioned response (UCR). The other stimuli were neutral because they did not produce fear.

When Albert was just over eleven months old, the rat and the UCS were presented together: as Albert reached out to stroke the animal, Watson struck the bar behind his head.

This occurred seven times in total over the next seven weeks. By this time, the rat, the conditioned stimulus (CS), on its own frightened Albert, and fear was now a conditioned response (CR).

The CR transferred spontaneously to the rabbit, the dog, and other stimuli that had been previously neutral. Five days after conditioning, the CR produced by the rat persisted. After ten days, it was ‘much less marked’, but it was still evident a month later.

Carter and Tiffany (1999) support the cue reactivity theory, they carried out a meta-analysis reviewing 41 cue-reactivity studies that compared responses of alcoholics, cigarette smokers, cocaine addicts and heroin addicts to drug-related versus neutral stimuli.

They found that dependent individuals reacted strongly to the cues presented and reported craving and physiological arousal.

Panic Disorder

Classical conditioning is thought to play an important role in the development of Pavlov (Bouton et al., 2002).

Panic disorder often begins after an initial “conditioning episode” involving an early panic attack. The panic attack serves as an unconditioned stimulus (US) that gets paired with neutral stimuli (conditioned stimuli or CS), allowing those stimuli to later trigger anxiety and panic reactions (conditioned responses or CRs).

The panic attack US can become associated with interoceptive cues (like increased heart rate) as well as external situational cues that are present during the attack. This allows those cues to later elicit anxiety and possibly panic (CRs).

Through this conditioning process, anxiety becomes focused on the possibility of having another panic attack. This anticipatory anxiety (a CR) is seen as a key step in the development of panic disorder, as it leads to heightened vigilance and sensitivity to bodily cues that can trigger future attacks.

The presence of conditioned anxiety can serve to potentiate or exacerbate future panic attacks. Anxiety cues essentially lower the threshold for panic. This helps explain how panic disorder can spiral after the initial conditioning episode.

Evidence suggests most patients with panic disorder recall an initial panic attack or conditioning event that preceded the disorder. Prospective studies also show conditioned anxiety and panic reactions can develop after an initial panic episode.

Classical conditioning processes are believed to often occur outside of conscious awareness in panic disorder, reflecting the operation of emotional neural systems separate from declarative knowledge systems.

Cue reactivity is the theory that people associate situations (e.g., meeting with friends)/ places (e.g., pub) with the rewarding effects of nicotine, and these cues can trigger a feeling of craving (Carter & Tiffany, 1999).

These factors become smoking-related cues. Prolonged use of nicotine creates an association between these factors and smoking based on classical conditioning.

Nicotine is the unconditioned stimulus (UCS), and the pleasure caused by the sudden increase in dopamine levels is the unconditioned response (UCR). Following this increase, the brain tries to lower the dopamine back to a normal level.

The stimuli that have become associated with nicotine were neutral stimuli (NS) before “learning” took place but they became conditioned stimuli (CS), with repeated pairings. They can produce the conditioned response (CR).

However, if the brain has not received nicotine, the levels of dopamine drop, and the individual experiences withdrawal symptoms therefore is more likely to feel the need to smoke in the presence of the cues that have become associated with the use of nicotine.

Classroom Learning

The implications of classical conditioning in the classroom are less important than those of operant conditioning , but there is still a need for teachers to try to make sure that students associate positive emotional experiences with learning.

If a student associates negative emotional experiences with school, then this can obviously have bad results, such as creating a school phobia.

For example, if a student is bullied at school they may learn to associate the school with fear. It could also explain why some students show a particular dislike of certain subjects that continue throughout their academic career. This could happen if a student is humiliated or punished in class by a teacher.

Principles of Classical Conditioning

Neutral stimulus.

In classical conditioning, a neutral stimulus (NS) is a stimulus that initially does not evoke a response until it is paired with the unconditioned stimulus.

For example, in Pavlov’s experiment, the bell was the neutral stimulus, and only produced a response when paired with food.

Unconditioned Stimulus

Unconditioned response.

In classical conditioning, an unconditioned response is an innate response that occurs automatically when the unconditioned stimulus is presented.

Pavlov showed the existence of the unconditioned response by presenting a dog with a bowl of food and measuring its salivary secretions.

Conditioned Stimulus

Conditioned response.

In classical conditioning, the conditioned response (CR) is the learned response to the previously neutral stimulus.

In Ivan Pavlov’s experiments in classical conditioning, the dog’s salivation was the conditioned response to the sound of a bell.

Acquisition

The process of pairing a neutral stimulus with an unconditioned stimulus to produce a conditioned response.

In the initial learning period, acquisition describes when an organism learns to connect a neutral stimulus and an unconditioned stimulus.

In psychology, extinction refers to the gradual weakening of a conditioned response by breaking the association between the conditioned and the unconditioned stimuli.

The weakening of a conditioned response occurs when the conditioned stimulus is repeatedly presented without the unconditioned stimulus.

For example, when the bell repeatedly rang, and no food was presented, Pavlov’s dog gradually stopped salivating at the sound of the bell.

Spontaneous Recovery

Spontaneous recovery is a phenomenon of Pavlovian conditioning that refers to the return of a conditioned response (in a weaker form) after a period of time following extinction.

It is the reappearance of an extinguished conditioned response after a rest period when the conditioned stimulus is presented alone.

For example, when Pavlov waited a few days after extinguishing the conditioned response, and then rang the bell once more, the dog salivated again.

Generalization

In psychology, generalization is the tendency to respond in the same way to stimuli similar (but not identical) to the original conditioned stimulus.

For example, in Pavlov’s experiment, if a dog is conditioned to salivate to the sound of a bell, it may later salivate to a higher-pitched bell.

Discrimination

In classical conditioning, discrimination is a process through which individuals learn to differentiate among similar stimuli and respond appropriately to each one.

For example, eventually, Pavlov’s dog learns the difference between the sound of the 2 bells and no longer salivates at the sound of the non-food bell.

Higher-Order Conditioning

Higher-order conditioning is when a conditioned stimulus is paired with a new neutral stimulus to create a second conditioned stimulus. For example, a bell (CS1) is paired with food (UCS) so that the bell elicits salivation (CR). Then, a light (NS) is paired with the bell.

Eventually, the light alone will elicit salivation, even without the presence of food. This demonstrates higher-order conditioning, where the conditioned stimulus (bell) serves as an unconditioned stimulus to condition a new stimulus (light).

Critical Evaluation

Practical applications.

The principles of classical conditioning have been widely and effectively applied in fields like behavioral therapy, education, and advertising. Therapies like systematic desensitization use classical conditioning to help eliminate phobias and anxiety.

The behaviorist approach has been used in the treatment of phobias, and systematic desensitization . The individual with the phobia is taught relaxation techniques and then makes a hierarchy of fear from the least frightening to the most frightening features of the phobic object.

He then is presented with the stimuli in that order and learns to associate (classical conditioning) the stimuli with a relaxation response. This is counter-conditioning.

Explaining involuntary behaviors

Classical conditioning helps explain some reflexive or involuntary behaviors like phobias, emotional reactions, and physiological responses. The model shows how these can be acquired through experience.

The process of classical conditioning can probably account for aspects of certain other mental disorders. For example, in post-traumatic stress disorder (PTSD), sufferers tend to show classically conditioned responses to stimuli present at the time of the traumatizing event (Charney et al., 1993).

However, since not everyone exposed to the traumatic event develops PTSD, other factors must be involved, such as individual differences in people’s appraisal of events as stressors and the recovery environment, such as family and support groups.

Supported by substantial experimental evidence

There is a wealth of experimental support for basic phenomena like acquisition, extinction, generalization, and discrimination. Pavlov’s original experiments on dogs and subsequent studies have demonstrated classical conditioning in animals and humans.

There have been many laboratory demonstrations of human participants acquiring behavior through classical conditioning. It is relatively easy to classically condition and extinguish conditioned responses, such as the eye-blink and galvanic skin responses.

A strength of classical conditioning theory is that it is scientific . This is because it’s based on empirical evidence carried out by controlled experiments . For example, Pavlov (1902) showed how classical conditioning could be used to make a dog salivate to the sound of a bell.

Supporters of a reductionist approach say that it is scientific. Breaking complicated behaviors down into small parts means that they can be scientifically tested. However, some would argue that the reductionist view lacks validity . Thus, while reductionism is useful, it can lead to incomplete explanations.

Ignores biological predispositions

Organisms are biologically prepared to associate certain stimuli over others. However, classical conditioning does not sufficiently account for innate predispositions and biases.

Classical conditioning emphasizes the importance of learning from the environment, and supports nurture over nature.

However, it is limiting to describe behavior solely in terms of either nature or nurture , and attempts to do this underestimate the complexity of human behavior. It is more likely that behavior is due to an interaction between nature (biology) and nurture (environment).

Lacks explanatory power

Classical conditioning provides limited insight into the cognitive processes underlying the associations it describes.

However, applying classical conditioning to our understanding of higher mental functions, such as memory, thinking, reasoning, or problem-solving, has proved more problematic.

Even behavior therapy, one of the more successful applications of conditioning principles to human behavior, has given way to cognitive–behavior therapy (Mackintosh, 1995).

Questionable ecological validity

While lab studies support classical conditioning, some question how well it holds up in natural settings. There is debate about how automatic and inevitable classical conditioning is outside the lab.

In normal adults, the conditioning process can be overridden by instructions: simply telling participants that the unconditioned stimulus will not occur causes an instant loss of the conditioned response, which would otherwise extinguish only slowly (Davey, 1983).

Most participants in an experiment are aware of the experimenter’s contingencies (the relationship between stimuli and responses) and, in the absence of such awareness often fail to show evidence of conditioning (Brewer, 1974).

Evidence indicates that for humans to exhibit classical conditioning, they need to be consciously aware of the connection between the conditioned stimulus (CS) and the unconditioned stimulus (US). This contradicts traditional theories that humans have two separate learning systems – one conscious and one unconscious – that allow conditioning to occur without conscious awareness (Lovibond & Shanks, 2002).

There are also important differences between very young children or those with severe learning difficulties and older children and adults regarding their behavior in a variety of operant conditioning and discrimination learning experiments.

These seem largely attributable to language development (Dugdale & Lowe, 1990). This suggests that people have rather more efficient, language-based forms of learning at their disposal than just the laborious formation of associations between a conditioned stimulus and an unconditioned stimulus.

Ethical concerns

The principles of classical conditioning raise ethical concerns about manipulating behavior without consent. This is especially true in advertising and politics.

• Manipulation of preferences – Classical conditioning can create positive associations with certain brands, products, or political candidates. This can manipulate preferences outside of a person’s rational thought process.
• Encouraging impulsive behaviors – Conditioning techniques may encourage behaviors like impulsive shopping, unhealthy eating, or risky financial choices by forging positive associations with these behaviors.
• Preying on vulnerabilities – Advertisers or political campaigns may exploit conditioning techniques to target and influence vulnerable demographic groups like youth, seniors, or those with mental health conditions.
• Reduction of human agency – At an extreme, the use of classical conditioning techniques reduces human beings to automata reacting predictably to stimuli. This is ethically problematic.

Deterministic theory

A final criticism of classical conditioning theory is that it is deterministic . This means it does not allow the individual any degree of free will. Accordingly, a person has no control over the reactions they have learned from classical conditioning, such as a phobia.

The deterministic approach also has important implications for psychology as a science. Scientists are interested in discovering laws that can be used to predict events.

However, by creating general laws of behavior, deterministic psychology underestimates the uniqueness of human beings and their freedom to choose their destiny.

The Role of Nature in Classical Conditioning

Behaviorists argue all learning is driven by experience, not nature. Classical conditioning exemplifies environmental influence. However, our evolutionary history predisposes us to learn some associations more readily than others. So nature also plays a role.

For example, PTSD develops in part due to strong conditioning during traumatic events. The emotions experienced during trauma lead to neural activity in the amygdala , creating strong associative learning between conditioned and unconditioned stimuli (Milad et al., 2009).

Individuals with PTSD show enhanced fear conditioning, reflected in greater amygdala reactivity to conditioned threat cues compared to trauma-exposed controls. In addition to strong initial conditioning, PTSD patients exhibit slower extinction to conditioned fear stimuli.

During extinction recall tests, PTSD patients fail to show differential skin conductance responses to extinguished versus non-extinguished cues, indicating impaired retention of fear extinction. Deficient extinction retention corresponds to reduced activation in the ventromedial prefrontal cortex and hippocampus and heightened dorsal anterior cingulate cortex response during extinction recall in PTSD patients.

In influential research on food conditioning, John Garcia found that rats easily learned to associate a taste with nausea from drugs, even if illness occurred hours later.

However, conditioning nausea to a sight or sound was much harder. This showed that conditioning does not occur equally for any stimulus pairing. Rather, evolution prepares organisms to learn some associations that aid survival more easily, like linking smells to illness.

The evolutionary significance of taste and nutrition ensures robust and resilient classical conditioning of flavor preferences, making them difficult to reverse (Hall, 2002).

Forming strong and lasting associations between flavors and nutrition aids survival by promoting the consumption of calorie-rich foods. This makes flavor conditioning very robust.

Repeated flavor-nutrition pairings in these studies lead to overlearning of the association, making it more resistant to extinction.

The learning is overtrained, context-specific, and subject to recovery effects that maintain the conditioned behavior despite extinction training.

Classical vs. operant condioning

In summary, classical conditioning is about passive stimulus-response associations, while operant conditioning is about actively connecting behaviors to consequences. Classical works on reflexes and operant on voluntary actions.

• Stimuli vs consequences : Classical conditioning focuses on associating two stimuli together. For example, pairing a bell (neutral stimulus) with food (reflex-eliciting stimulus) creates a conditioned response of salivation to the bell. Operant conditioning is about connecting behaviors with the consequences that follow. If a behavior is reinforced, it will increase. If it’s punished, it will decrease.
• Passive vs. active : In classical conditioning, the organism is passive and automatically responds to the conditioned stimulus. Operant conditioning requires the organism to perform a behavior that then gets reinforced or punished actively. The organism operates on the environment.
• Involuntary vs. voluntary : Classical conditioning works with involuntary, reflexive responses like salivation, blinking, etc. Operant conditioning shapes voluntary behaviors that are controlled by the organism, like pressing a lever.
• Association vs. reinforcement : Classical conditioning relies on associating stimuli in order to create a conditioned response. Operant conditioning depends on using reinforcement and punishment to increase or decrease voluntary behaviors.

Learning Check

• In Ivan Pavlov’s famous experiment, he rang a bell before presenting food powder to dogs. Eventually, the dogs salivated at the mere sound of the bell. Identify the neutral stimulus, unconditioned stimulus, unconditioned response, conditioned stimulus, and conditioned response in Pavlov’s experiment.
• A student loves going out for pizza and beer with friends on Fridays after class. Whenever one friend texts the group about Friday plans, the student immediately feels happy and excited. The friend starts texting the group on Thursdays when she wants the student to feel happier. Explain how this is an example of classical conditioning. Identify the UCS, UCR, CS, and CR.
• A college student is traumatized after a car accident. She now feels fear every time she gets into a car. How could extinction be used to eliminate this acquired fear?
• A professor always slams their book on the lectern right before giving a pop quiz. Students now feel anxiety whenever they hear the book slam. Is this classical conditioning? If so, identify the NS, UCS, UCR, CS, and CR.
• Contrast classical conditioning and operant conditioning. How are they similar and different? Provide an original example of each type of conditioning.
• How could the principles of classical conditioning be applied to help students overcome test anxiety?
• Explain how taste aversion learning is an adaptive form of classical conditioning. Provide an original example.
• What is second-order conditioning? Give an example and identify the stimuli and responses.
• What is the role of extinction in classical conditioning? How could extinction be used in cognitive behavioral therapy for anxiety disorders?

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Bremner, J. D., Southwick, S. M., Johnson, D. R., Yehuda, R., & Charney, D. S. (1993). Childhood physical abuse and combat-related posttraumatic stress disorder in Vietnam veterans.  The American journal of psychiatry .

Brewer, W. F. (1974). There is no convincing evidence for operant or classical conditioning in adult humans.

Carter, B. L., & Tiffany, S. T. (1999). Meta‐analysis of cue‐reactivity in addiction research.  Addiction, 94 (3), 327-340.

Davey, B. (1983). Think aloud: Modeling the cognitive processes of reading comprehension.  Journal of Reading, 27 (1), 44-47.

Dugdale, N., & Lowe, C. F. (1990). Naming and stimulus equivalence.

Garcia, J., Ervin, F. R., & Koelling, R. A. (1966). Learning with prolonged delay of reinforcement. Psychonomic Science, 5 (3), 121–122.

Garcia, J., Kimeldorf, D. J., & Koelling, R. A. (1955). Conditioned aversion to saccharin resulting from exposure to gamma radiation.  Science, 122 , 157–158.

Hall, G. (2022). Extinction of conditioned flavor preferences.  Journal of Experimental Psychology: Animal Learning and Cognition .

Logan, C. A. (2002). When scientific knowledge becomes scientific discovery: The disappearance of classical conditioning before Pavlov .  Journal of the History of the Behavioral Sciences ,  38 (4), 393-403.

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Milad, M. R., Pitman, R. K., Ellis, C. B., Gold, A. L., Shin, L. M., Lasko, N. B.,…Rauch, S. L. (2009). Neurobiological basis of failure to recall extinction memory in posttraumatic stress disorder.  Biological Psychiatry, 66 (12), 1075–82.

Pavlov, I. P. (1897/1902).  The work of the digestive glands . London: Griffin.

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Watson, J. B., & Rayner, R. (1920).  Conditioned emotional reactions .  Journal of experimental psychology, 3 (1), 1.

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7.1 Learning by Association: Classical Conditioning

Learning objectives.

• Describe how Pavlov’s early work in classical conditioning influenced the understanding of learning.
• Review the concepts of classical conditioning, including unconditioned stimulus (US), conditioned stimulus (CS), unconditioned response (UR), and conditioned response (CR).
• Explain the roles that extinction, generalization, and discrimination play in conditioned learning.

Pavlov Demonstrates Conditioning in Dogs

In the early part of the 20th century, Russian physiologist Ivan Pavlov (1849–1936) was studying the digestive system of dogs when he noticed an interesting behavioral phenomenon: The dogs began to salivate when the lab technicians who normally fed them entered the room, even though the dogs had not yet received any food. Pavlov realized that the dogs were salivating because they knew that they were about to be fed; the dogs had begun to associate the arrival of the technicians with the food that soon followed their appearance in the room.

Figure 7.2 Ivan Pavlov

Ivan Pavlov’s research made substantial contributions to our understanding of learning.

LIFE Photo Archive – Wikimedia Commons – public domain.

With his team of researchers, Pavlov began studying this process in more detail. He conducted a series of experiments in which, over a number of trials, dogs were exposed to a sound immediately before receiving food. He systematically controlled the onset of the sound and the timing of the delivery of the food, and recorded the amount of the dogs’ salivation. Initially the dogs salivated only when they saw or smelled the food, but after several pairings of the sound and the food, the dogs began to salivate as soon as they heard the sound. The animals had learned to associate the sound with the food that followed.

Pavlov had identified a fundamental associative learning process called classical conditioning . Classical conditioning refers to learning that occurs when a neutral stimulus (e.g., a tone) becomes associated with a stimulus (e.g., food) that naturally produces a behavior . After the association is learned, the previously neutral stimulus is sufficient to produce the behavior.

As you can see in Figure 7.3 “4-Panel Image of Whistle and Dog” , psychologists use specific terms to identify the stimuli and the responses in classical conditioning. The unconditioned stimulus (US) is something (such as food) that triggers a natural occurring response , and the unconditioned response (UR) is the naturally occurring response (such as salivation) that follows the unconditioned stimulus . The conditioned stimulus (CS) is a neutral stimulus that, after being repeatedly presented prior to the unconditioned stimulus, evokes a similar response as the unconditioned stimulus . In Pavlov’s experiment, the sound of the tone served as the conditioned stimulus that, after learning, produced the conditioned response (CR) , which is the acquired response to the formerly neutral stimulus . Note that the UR and the CR are the same behavior—in this case salivation—but they are given different names because they are produced by different stimuli (the US and the CS, respectively).

Figure 7.3 4-Panel Image of Whistle and Dog

Top left: Before conditioning, the unconditioned stimulus (US) naturally produces the unconditioned response (UR). Top right: Before conditioning, the neutral stimulus (the whistle) does not produce the salivation response. Bottom left: The unconditioned stimulus (US), in this case the food, is repeatedly presented immediately after the neutral stimulus. Bottom right: After learning, the neutral stimulus (now known as the conditioned stimulus or CS), is sufficient to produce the conditioned responses (CR).

Conditioning is evolutionarily beneficial because it allows organisms to develop expectations that help them prepare for both good and bad events. Imagine, for instance, that an animal first smells a new food, eats it, and then gets sick. If the animal can learn to associate the smell (CS) with the food (US), then it will quickly learn that the food creates the negative outcome, and not eat it the next time.

The Persistence and Extinction of Conditioning

After he had demonstrated that learning could occur through association, Pavlov moved on to study the variables that influenced the strength and the persistence of conditioning. In some studies, after the conditioning had taken place, Pavlov presented the sound repeatedly but without presenting the food afterward. Figure 7.4 “Acquisition, Extinction, and Spontaneous Recovery” shows what happened. As you can see, after the intial acquisition (learning) phase in which the conditioning occurred, when the CS was then presented alone, the behavior rapidly decreased—the dogs salivated less and less to the sound, and eventually the sound did not elicit salivation at all. Extinction refers to the reduction in responding that occurs when the conditioned stimulus is presented repeatedly without the unconditioned stimulus .

Figure 7.4 Acquisition, Extinction, and Spontaneous Recovery

Acquisition: The CS and the US are repeatedly paired together and behavior increases. Extinction: The CS is repeatedly presented alone, and the behavior slowly decreases. Spontaneous recovery: After a pause, when the CS is again presented alone, the behavior may again occur and then again show extinction.

Although at the end of the first extinction period the CS was no longer producing salivation, the effects of conditioning had not entirely disappeared. Pavlov found that, after a pause, sounding the tone again elicited salivation, although to a lesser extent than before extinction took place. The increase in responding to the CS following a pause after extinction is known as spontaneous recovery . When Pavlov again presented the CS alone, the behavior again showed extinction until it disappeared again.

Although the behavior has disappeared, extinction is never complete. If conditioning is again attempted, the animal will learn the new associations much faster than it did the first time.

Pavlov also experimented with presenting new stimuli that were similar, but not identical to, the original conditioned stimulus. For instance, if the dog had been conditioned to being scratched before the food arrived, the stimulus would be changed to being rubbed rather than scratched. He found that the dogs also salivated upon experiencing the similar stimulus, a process known as generalization . Generalization refers to the tendency to respond to stimuli that resemble the original conditioned stimulus . The ability to generalize has important evolutionary significance. If we eat some red berries and they make us sick, it would be a good idea to think twice before we eat some purple berries. Although the berries are not exactly the same, they nevertheless are similar and may have the same negative properties.

Lewicki (1985) conducted research that demonstrated the influence of stimulus generalization and how quickly and easily it can happen. In his experiment, high school students first had a brief interaction with a female experimenter who had short hair and glasses. The study was set up so that the students had to ask the experimenter a question, and (according to random assignment) the experimenter responded either in a negative way or a neutral way toward the students. Then the students were told to go into a second room in which two experimenters were present, and to approach either one of them. However, the researchers arranged it so that one of the two experimenters looked a lot like the original experimenter, while the other one did not (she had longer hair and no glasses). The students were significantly more likely to avoid the experimenter who looked like the earlier experimenter when that experimenter had been negative to them than when she had treated them more neutrally. The participants showed stimulus generalization such that the new, similar-looking experimenter created the same negative response in the participants as had the experimenter in the prior session.

The flip side of generalization is discrimination — the tendency to respond differently to stimuli that are similar but not identical . Pavlov’s dogs quickly learned, for example, to salivate when they heard the specific tone that had preceded food, but not upon hearing similar tones that had never been associated with food. Discrimination is also useful—if we do try the purple berries, and if they do not make us sick, we will be able to make the distinction in the future. And we can learn that although the two people in our class, Courtney and Sarah, may look a lot alike, they are nevertheless different people with different personalities.

In some cases, an existing conditioned stimulus can serve as an unconditioned stimulus for a pairing with a new conditioned stimulus —a process known as second-order conditioning . In one of Pavlov’s studies, for instance, he first conditioned the dogs to salivate to a sound, and then repeatedly paired a new CS, a black square, with the sound. Eventually he found that the dogs would salivate at the sight of the black square alone, even though it had never been directly associated with the food. Secondary conditioners in everyday life include our attractions to things that stand for or remind us of something else, such as when we feel good on a Friday because it has become associated with the paycheck that we receive on that day, which itself is a conditioned stimulus for the pleasures that the paycheck buys us.

The Role of Nature in Classical Conditioning

As we have seen in Chapter 1 “Introducing Psychology” , scientists associated with the behavioralist school argued that all learning is driven by experience, and that nature plays no role. Classical conditioning, which is based on learning through experience, represents an example of the importance of the environment. But classical conditioning cannot be understood entirely in terms of experience. Nature also plays a part, as our evolutionary history has made us better able to learn some associations than others.

Clinical psychologists make use of classical conditioning to explain the learning of a phobia — a strong and irrational fear of a specific object, activity, or situation . For example, driving a car is a neutral event that would not normally elicit a fear response in most people. But if a person were to experience a panic attack in which he suddenly experienced strong negative emotions while driving, he may learn to associate driving with the panic response. The driving has become the CS that now creates the fear response.

Psychologists have also discovered that people do not develop phobias to just anything. Although people may in some cases develop a driving phobia, they are more likely to develop phobias toward objects (such as snakes, spiders, heights, and open spaces) that have been dangerous to people in the past. In modern life, it is rare for humans to be bitten by spiders or snakes, to fall from trees or buildings, or to be attacked by a predator in an open area. Being injured while riding in a car or being cut by a knife are much more likely. But in our evolutionary past, the potential of being bitten by snakes or spiders, falling out of a tree, or being trapped in an open space were important evolutionary concerns, and therefore humans are still evolutionarily prepared to learn these associations over others (Öhman & Mineka, 2001; LoBue & DeLoache, 2010).

Another evolutionarily important type of conditioning is conditioning related to food. In his important research on food conditioning, John Garcia and his colleagues (Garcia, Kimeldorf, & Koelling, 1955; Garcia, Ervin, & Koelling, 1966) attempted to condition rats by presenting either a taste, a sight, or a sound as a neutral stimulus before the rats were given drugs (the US) that made them nauseous. Garcia discovered that taste conditioning was extremely powerful—the rat learned to avoid the taste associated with illness, even if the illness occurred several hours later. But conditioning the behavioral response of nausea to a sight or a sound was much more difficult. These results contradicted the idea that conditioning occurs entirely as a result of environmental events, such that it would occur equally for any kind of unconditioned stimulus that followed any kind of conditioned stimulus. Rather, Garcia’s research showed that genetics matters—organisms are evolutionarily prepared to learn some associations more easily than others. You can see that the ability to associate smells with illness is an important survival mechanism, allowing the organism to quickly learn to avoid foods that are poisonous.

Classical conditioning has also been used to help explain the experience of posttraumatic stress disorder (PTSD), as in the case of P. K. Philips described in the chapter opener. PTSD is a severe anxiety disorder that can develop after exposure to a fearful event, such as the threat of death (American Psychiatric Association, 1994). PTSD occurs when the individual develops a strong association between the situational factors that surrounded the traumatic event (e.g., military uniforms or the sounds or smells of war) and the US (the fearful trauma itself). As a result of the conditioning, being exposed to, or even thinking about the situation in which the trauma occurred (the CS), becomes sufficient to produce the CR of severe anxiety (Keane, Zimering, & Caddell, 1985).

Posttraumatic stress disorder (PTSD) represents a case of classical conditioning to a severe trauma that does not easily become extinct. In this case the original fear response, experienced during combat, has become conditioned to a loud noise. When the person with PTSD hears a loud noise, she experiences a fear response even though she is now far from the site of the original trauma.

Marc Wathieu – Luigi Coppola – CC BY-NC 2.0.

PTSD develops because the emotions experienced during the event have produced neural activity in the amygdala and created strong conditioned learning. In addition to the strong conditioning that people with PTSD experience, they also show slower extinction in classical conditioning tasks (Milad et al., 2009). In short, people with PTSD have developed very strong associations with the events surrounding the trauma and are also slow to show extinction to the conditioned stimulus.

Key Takeaways

• In classical conditioning, a person or animal learns to associate a neutral stimulus (the conditioned stimulus, or CS) with a stimulus (the unconditioned stimulus, or US) that naturally produces a behavior (the unconditioned response, or UR). As a result of this association, the previously neutral stimulus comes to elicit the same response (the conditioned response, or CR).
• Extinction occurs when the CS is repeatedly presented without the US, and the CR eventually disappears, although it may reappear later in a process known as spontaneous recovery.
• Stimulus generalization occurs when a stimulus that is similar to an already-conditioned stimulus begins to produce the same response as the original stimulus does.
• Stimulus discrimination occurs when the organism learns to differentiate between the CS and other similar stimuli.
• In second-order conditioning, a neutral stimulus becomes a CS after being paired with a previously established CS.
• Some stimuli—response pairs, such as those between smell and food—are more easily conditioned than others because they have been particularly important in our evolutionary past.

Exercises and Critical Thinking

• A teacher places gold stars on the chalkboard when the students are quiet and attentive. Eventually, the students start becoming quiet and attentive whenever the teacher approaches the chalkboard. Can you explain the students’ behavior in terms of classical conditioning?
• Recall a time in your life, perhaps when you were a child, when your behaviors were influenced by classical conditioning. Describe in detail the nature of the unconditioned and conditioned stimuli and the response, using the appropriate psychological terms.
• If posttraumatic stress disorder (PTSD) is a type of classical conditioning, how might psychologists use the principles of classical conditioning to treat the disorder?

American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.). Washington, DC: Author.

Garcia, J., Ervin, F. R., & Koelling, R. A. (1966). Learning with prolonged delay of reinforcement. Psychonomic Science, 5 (3), 121–122.

Garcia, J., Kimeldorf, D. J., & Koelling, R. A. (1955). Conditioned aversion to saccharin resulting from exposure to gamma radiation. Science, 122 , 157–158.

Keane, T. M., Zimering, R. T., & Caddell, J. M. (1985). A behavioral formulation of posttraumatic stress disorder in Vietnam veterans. The Behavior Therapist, 8 (1), 9–12.

Lewicki, P. (1985). Nonconscious biasing effects of single instances on subsequent judgments. Journal of Personality and Social Psychology, 48 , 563–574.

LoBue, V., & DeLoache, J. S. (2010). Superior detection of threat-relevant stimuli in infancy. Developmental Science, 13 (1), 221–228.

Milad, M. R., Pitman, R. K., Ellis, C. B., Gold, A. L., Shin, L. M., Lasko, N. B.,…Rauch, S. L. (2009). Neurobiological basis of failure to recall extinction memory in posttraumatic stress disorder. Biological Psychiatry, 66 (12), 1075–82.

Öhman, A., & Mineka, S. (2001). Fears, phobias, and preparedness: Toward an evolved module of fear and fear learning. Psychological Review, 108 (3), 483–522.

Introduction to Psychology Copyright © 2015 by University of Minnesota is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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• Coon, D.J. (1982). Eponymy, obscurity, Twitmyer, and Pavlov. Journal of the History of Behavioral Science . 18 (3). 255-62.
• Pavlov, I.P. (1927). Conditioned Reflexes: An investigation of the physiological activity of the cerebral cortex. Retrieved from http://psychclassics.yorku.ca/Pavlov/ .
• Craik, F.I.M. and Lockhart, R.S. (1972). Levels of Processing: A Framework for Memory Research. Journal of Verbal Learning and Visual Behavior . 11 (6). 671-684.
• Carr, H. and Freeman A. (1919). Time relationships in the formation of associations. Psychology Review . 26 (6). 335-353.
• Pavlov, I.P. (1927). Conditioned Reflexes: An investigation of the physiological activity of the cerebral cortex. Retrieved from http://psychclassics.yorku.ca/Pavlov/lecture6.htm .
• Kirkpatrick, K and Church, R.M. (2003). Tracking of the expected time to reinforcement in temporal conditioning processes. Learning & Behavior . 31 (1). 3-21.
• Meulders A, Vandebroek, N. Vervliet, B. and Vlaeyen, J.W.S. (2013). Generalization Gradients in Cued and Contextual Pain-Related Fear: An Experimental Study in Health Participants. Frontiers in Human Neuroscience , 7 (345). 1-12.
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Pavlov’s Dog: The Psychology Experiment That Changed Everything

Pavlov’s Dog is a well-known experiment in psychology that has been taught for decades. Ivan Pavlov , a Russian physiologist, discovered classical conditioning through his experiments with dogs. He found that dogs could be trained to associate a sound with food, causing them to salivate at the sound alone.

The experiment began with Pavlov ringing a bell every time he fed his dogs. After a while, the dogs began to associate the sound of the bell with food and would salivate at the sound alone, even if no food was present. This became known as a conditioned response, where a previously neutral stimulus (the bell) became associated with a natural response (salivating).

The experiment has been used to explain many psychological phenomena, including addiction, phobias, and anxiety. It has also been applied in therapy, where patients can learn to associate positive experiences with previously negative stimuli. The Pavlov’s Dog experiment is a crucial part of psychology’s history and continues to be studied today.

Pavlov’s Life and Career

Ivan Pavlov was a Russian physiologist who lived from 1849 to 1936. He is best known for his work in classical conditioning, a type of learning that occurs when a neutral stimulus is consistently paired with a stimulus that elicits a response. Pavlov was born in Ryazan, Russia, and studied at the University of St. Petersburg, where he received his doctorate in 1879.

Pavlov’s early research focused on the digestive system, and he discovered that the secretion of gastric juice was not a passive process but rather a response to stimuli. This led him to develop the concept of the conditioned reflex, which he explored in detail in his famous experiments with dogs.

In these experiments, Pavlov trained dogs to associate the sound of a bell with food presentation. Over time, the dogs began to salivate at the sound of the bell, even when no food was present. This demonstrated that a neutral stimulus (the bell) could become associated with a natural response (salivation) through repeated pairings with a stimulus that elicits that response (food).

Pavlov’s work had a profound impact on the field of psychology, and his ideas continue to influence research today. He was awarded the Nobel Prize in Physiology or Medicine in 1904 for his work on the physiology of digestion. Still, his legacy is best remembered for his contributions to the study of learning and behavior.

Classical Conditioning

Classical conditioning is a type of learning that occurs when a neutral stimulus is repeatedly paired with a stimulus that naturally elicits a response. Over time, the neutral stimulus becomes associated with the natural stimulus and begins to produce the same response. Russian physiologist Ivan Pavlov first studied this type of learning in the late 1800s.

One of the most famous examples of classical conditioning is Pavlov’s experiment with dogs. In this experiment, Pavlov rang a bell every time he fed the dogs. Eventually, the dogs began to salivate at the sound of the bell, even when no food was present. The sound of the bell had become associated with the food, and the dogs had learned to associate the two stimuli.

Classical conditioning can be used to explain a variety of behaviors and responses. For example, a person who has been in a car accident may develop a fear of driving. The sound of screeching tires or the sight of a car may become associated with the traumatic experience, causing the person to feel anxious or fearful when driving.

Classical conditioning can also be used to treat certain types of phobias and anxiety disorders. By gradually exposing a person to the feared stimulus in a safe and controlled environment, the person can learn to associate the stimulus with safety and relaxation rather than fear and anxiety.

Classical conditioning is a powerful tool for understanding how we learn and respond to environmental stimuli. By understanding the principles of classical conditioning, we can better understand our behaviors and emotions, as well as those of others around us.

Pavlov’s Experiments

Pavlov’s experiments with dogs revolutionized the field of psychology and laid the foundation for the study of classical conditioning. In this section, we will explore two aspects of his experiments: salivating dogs and conditioned responses.

Salivating Dogs

Pavlov observed that dogs would salivate when presented with food. However, he also noticed that the dogs would start salivating before the food was presented. This led him to hypothesize that the dogs were responding not just to the food but to other associated stimuli, such as the sound of the food being prepared or the sight of the person who fed them.

To test his hypothesis, Pavlov began a series of experiments where he would ring a bell before presenting the dogs with food. After a few repetitions, the dogs began to salivate at the sound of the bell alone, even when no food was present. This demonstrated that the dogs had learned to associate the sound of the bell with the presence of food and were responding accordingly.

Conditioned Response

Pavlov’s experiments with dogs led to the discovery of the conditioned response, the learned response to a previously neutral stimulus. In the case of Pavlov’s dogs, the sound of the bell was originally a neutral stimulus. Still, it became associated with food and, therefore, elicited a response (salivation) from the dogs.

The conditioned response is an essential concept in psychology, as it helps to explain how we learn to respond to various stimuli in our environment. For example, if we have a positive experience with a particular food, we may develop a conditioned response to the sight or smell of that food, even if we are not hungry.

Pavlov’s experiments with dogs were groundbreaking in psychology and led to the discovery of classical conditioning and the conditioned response. By demonstrating that animals (and humans) can learn to respond to previously neutral stimuli, Pavlov paved the way for further research into the mechanisms of learning and behavior.

Significance in Psychology

Pavlov’s dog experiment has been a significant discovery in psychology. It has paved the way for developing various theories and has been instrumental in understanding human behavior. In this section, we will discuss the significance of Pavlov’s dog experiment in the context of behaviorism and learning theories.

Behaviorism

Pavlov’s dog experiment has been a cornerstone in the development of behaviorism. Behaviorism is a school of thought in psychology that emphasizes the importance of observable behavior rather than internal mental states. Pavlov’s experiment demonstrated how a stimulus-response connection could be formed through conditioning. This concept has been used to explain various behaviors, such as phobias and addictions.

Learning Theories

Pavlov’s dog experiment has also been significant in developing learning theories . Learning theories are concerned with how people acquire new knowledge and skills. Pavlov’s experiment demonstrated how classical conditioning could teach animals new behaviors. This concept has been used to explain various learning phenomena, such as the acquisition of language and the development of social skills.

In conclusion, Pavlov’s dog experiment has been a significant discovery in psychology. It has been instrumental in the development of behaviorism and learning theories. By understanding the principles of classical conditioning, we can better understand human behavior and how we learn new skills and behaviors.

Implications in Modern Psychology

Pavlov’s dog experiments have had a significant impact on modern psychology. His theory of classical conditioning has become a cornerstone of behaviorism, a school of thought that dominated psychology in the early 20th century. Today, it continues to influence psychologists and researchers in various fields.

One of the most significant implications of Pavlov’s work is the understanding of how learning takes place. His experiments showed that animals, including humans, can learn through association. This concept has been applied in many areas of modern psychology, including education, advertising, and even politics.

For example, in education, classical conditioning can improve students’ learning by associating positive experiences with specific subjects or activities. In advertising, classical conditioning can create positive associations between a product and a particular emotion or experience, influencing consumers’ purchasing decisions.

Moreover, Pavlov’s work has also contributed to developing other learning theories, such as operant conditioning, which focuses on the consequences of behavior rather than the stimuli that precede it. These theories have been used to explain various human behaviors, from addiction to language acquisition.

Pavlov’s dog experiments have had a lasting impact on modern psychology. His theory of classical conditioning has contributed to our understanding of how learning takes place and has been applied in various fields, from education to advertising. His work has also influenced the development of other learning theories, making it a crucial part of studying human behavior.

Criticism and Controversies

While Pavlov’s experiments have been foundational in psychology, they have also been subject to criticism and controversy. Here are a few examples:

• Animal cruelty:  Some critics argue that Pavlov’s experiments on dogs were cruel and unethical. The dogs were often subjected to painful surgeries and kept in small cages for long periods. While these practices were common in the early 20th century, they would not be acceptable by today’s ethical standards.
• Oversimplification of behavior:  Pavlov’s experiments focused on classical conditioning, which suggests that behavior is determined solely by external stimuli. However, this oversimplifies the complex nature of human behavior, which is influenced by various factors, including genetics, environment, and personal experience.
• Limited generalizability:  Pavlov’s experiments were conducted on dogs, which may not accurately reflect human behavior. While some of the principles of classical conditioning may apply to humans, it is essential to recognize that there are also significant differences between species.
• Misinterpretation of results:  Pavlov’s work has been subject to misinterpretation over the years. For example, many people believe that Pavlov’s dogs learned to salivate at the sound of a bell because they associated it with food. However, this is only partially accurate. The dogs learned to associate the sound of the bell with the experimenter’s presence, who would then provide the food.

Frequently Asked Questions

What were the basic features of classical conditioning discovered by pavlov.

Classical conditioning is a type of learning in which a neutral stimulus becomes associated with a meaningful stimulus, resulting in a behavioral response. Pavlov discovered that when a neutral stimulus (such as a bell) was repeatedly paired with a meaningful stimulus (such as food), the neutral stimulus alone could elicit the same response (such as salivation) as the meaningful stimulus.

What was the purpose of Pavlov’s dog experiment?

Pavlov’s dog experiment was designed to study the process of classical conditioning. He wanted to understand how dogs learn to associate a neutral stimulus (such as a bell) with a meaningful stimulus (such as food) and how this association leads to a behavioral response (such as salivation).

How did Pavlov’s experiments contribute to the development of psychology?

Pavlov’s experiments were groundbreaking in the field of psychology. They provided evidence for the concept of classical conditioning, which has since been used to explain a wide range of human and animal behaviors. Pavlov’s work also paved the way for the development of behaviorism, a school of psychology that emphasizes the importance of observable behavior in understanding human and animal psychology.

What is the Pavlovian response and how does it work?

The Pavlovian response is a learned response to a previously neutral stimulus. It works by pairing the neutral stimulus with a meaningful stimulus, which leads to the formation of an association between the two. Once the association is formed, the neutral stimulus alone can elicit the same response as the meaningful stimulus.

How is Pavlovian conditioning used in dog training?

Pavlovian conditioning is often used in dog training to teach dogs new behaviors or to modify existing ones. For example, a trainer might use a clicker (a neutral stimulus) to signal to a dog that it has performed a desired behavior (a meaningful stimulus), and then reward the dog with a treat. Over time, the dog will learn to associate the clicker with the reward and will perform the desired behavior without the need for a treat.

What is the Pavlovian response in humans and how is it studied?

The Pavlovian response in humans is similar to that in dogs: it involves the formation of an association between a neutral stimulus and a meaningful stimulus, resulting in a learned response. This response has been studied in a variety of contexts, including addiction, phobias, and taste aversions. Researchers use a variety of methods to study the Pavlovian response in humans, including brain imaging techniques and behavioral experiments.

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Classical Conditioning

Learning objectives.

• Explain how classical conditioning occurs
• Identify the NS, UCS, UCR, CS, and CR in classical conditioning situations

Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you have heard of Pavlov and his famous dogs.

Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his experiments in classical conditioning (Figure 1). As we discussed briefly in the previous section, classical conditioning is a process by which we learn to associate stimuli and, consequently, to anticipate events.

Figure 1 . Ivan Pavlov’s research on the digestive system of dogs unexpectedly led to his discovery of the learning process now known as classical conditioning.

Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist, not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). In his studies with dogs, Pavlov measured the amount of saliva produced in response to various foods. Over time, Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food, at the sight of an empty food bowl, and even at the sound of the laboratory assistants’ footsteps. Salivating to food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of an empty bowl or the sound of footsteps.

These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs’ “psychic secretions” (Pavlov, 1927). To explore this phenomenon in an objective manner, Pavlov designed a series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a bell, a light, and a touch on the leg. Through his experiments, Pavlov realized that an organism has two types of responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned (learned) responses.

In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder in this situation was an unconditioned stimulus (UCS) : a stimulus that elicits a reflexive response in an organism. The dogs’ salivation was an unconditioned response (UCR) : a natural (unlearned) reaction to a given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:

In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus. Pavlov would sound a tone (like ringing a bell) and then give the dogs the meat powder (Figure 2). The tone was the neutral stimulus (NS), which is a stimulus that does not naturally elicit a response. Prior to conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for the dogs. Quite simply this pairing means:

When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned stimulus (CS) , which is a stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the sound of the assistants’ footsteps. The behavior caused by the conditioned stimulus is called the conditioned response (CR) . In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they began to salivate (CR) in anticipation of food.

Figure 2 . Before conditioning, an unconditioned stimulus (food) produces an unconditioned response (salivation), and a neutral stimulus (bell) does not produce a response. During conditioning, the unconditioned stimulus (food) is presented repeatedly just after the presentation of the neutral stimulus (bell). After conditioning, the neutral stimulus alone produces a conditioned response (salivation), thus becoming a conditioned stimulus.

View the following video to learn more about Pavlov and his dogs:

You can view the transcript for “Classical Conditioning – Ivan Pavlov” here (opens in new window) .

Real World Application of Classical Conditioning

How does classical conditioning work in the real world? Consider the case of Moisha, who was diagnosed with cancer. When she received her first chemotherapy treatment, she vomited shortly after the chemicals were injected. In fact, every trip to the doctor for chemotherapy treatment shortly after the drugs were injected, she vomited. Moisha’s treatment was a success and her cancer went into remission. Now, when she visits her oncologist’s office every 6 months for a check-up, she becomes nauseous. In this case, the chemotherapy drugs are the unconditioned stimulus (UCS), vomiting is the unconditioned response (UCR), the doctor’s office is the conditioned stimulus (CS) after being paired with the UCS, and nausea is the conditioned response (CR). Let’s assume that the chemotherapy drugs that Moisha takes are given through a syringe injection. After entering the doctor’s office, Moisha sees a syringe, and then gets her medication. In addition to the doctor’s office, Moisha will learn to associate the syringe with the medication and will respond to syringes with nausea. This is an example of higher-order (or second-order) conditioning, when the conditioned stimulus (the doctor’s office) serves to condition another stimulus (the syringe). It is hard to achieve anything above second-order conditioning. For example, if someone rang a bell every time Moisha received a syringe injection of chemotherapy drugs in the doctor’s office, Moisha likely will never get sick in response to the bell.

Consider another example of classical conditioning. Let’s say you have a cat named Tiger, who is quite spoiled. You keep her food in a separate cabinet, and you also have a special electric can opener that you use only to open cans of cat food. For every meal, Tiger hears the distinctive sound of the electric can opener (“zzhzhz”) and then gets her food. Tiger quickly learns that when she hears “zzhzhz” she is about to get fed. What do you think Tiger does when she hears the electric can opener? She will likely get excited and run to where you are preparing her food. This is an example of classical conditioning. In this case, what are the UCS, CS, UCR, and CR?

What if the cabinet holding Tiger’s food becomes squeaky? In that case, Tiger hears “squeak” (the cabinet), “zzhzhz” (the electric can opener), and then she gets her food. Tiger will learn to get excited when she hears the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus (“zzhzhz”) is called higher-order conditioning, or second-order conditioning. This means you are using the conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet (Figure 3). It is hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet (“squeak”), use the can opener (“zzhzhz”), and then feed Tiger, Tiger will likely never get excited when hearing the bell alone.

Figure 3 . In higher-order conditioning, an established conditioned stimulus is paired with a new neutral stimulus (the second-order stimulus), so that eventually the new stimulus also elicits the conditioned response, without the initial conditioned stimulus being presented.

Everyday Connection: Classical Conditioning at Stingray City

Figure 4 . Kate holds a southern stingray at Stingray City in the Cayman Islands. These stingrays have been classically conditioned to associate the sound of a boat motor with food provided by tourists. (credit: Kathryn Dumper)

Kate and her husband Scott recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary stingrays have become accustomed to interacting with humans. About 40 years ago, fishermen began to clean fish and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays would swim in to eat (unconditioned response) what the fishermen threw into the water; this continued for years. By the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs. When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know that they will get to eat (conditioned response).

As soon as Kate and Scott reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped into the water with bags of squid, the stingrays’ favorite treat. The swarm of stingrays bumped and rubbed up against their legs like hungry cats (Figure 4). Kate and Scott were able to feed, pet, and even kiss (for luck) these amazing creatures. Then all the squid was gone, and so were the stingrays.

Classical conditioning also applies to humans, even babies. For example, Sara buys formula in blue canisters for her six-month-old daughter, Angelina. Whenever Sara takes out a formula container, Angelina gets excited, tries to reach toward the food, and most likely salivates. Why does Angelina get excited when she sees the formula canister? What are the UCS, CS, UCR, and CR here?

So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set boundaries.

For a humorous look at conditioning, you can watch an example from the television show  The Office . Jim conducts an experiment in which he offers Dwight a breath mint every time Jim’s computer makes a specific sound. After repeating this several times, he eventually conditions Dwight to automatically expect a breath mint upon hearing that sound.   See if you can identify the NS, UCS, UCR, CS, and CR.

Review the classical conditioning concepts yet again by walking through Pavlov’s research in the following interactive:

Think It Over

Can you think of an example in your life of how classical conditioning has produced a positive emotional response, such as happiness or excitement? How about a negative emotional response, such as fear, anxiety, or anger?

• Modification and adaptation, addition of tutorial. Provided by : Lumen Learning. License : CC BY: Attribution
• Classical conditioning interactive. Authored by : Jessica Traylor for Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution
• Classical Conditioning. Authored by : OpenStax College. Located at : https://openstax.org/books/psychology-2e/pages/6-2-classical-conditioning . License : CC BY: Attribution . License Terms : Download for free at https://openstax.org/books/psychology-2e/pages/1-introduction
• Classical Conditioning - Ivan Pavlov. Authored by : BullyingNewsVideos. Located at : https://www.youtube.com/watch?v=hhqumfpxuzI . License : Other . License Terms : Standard YouTube License
• The Office Classical Conditioning. Authored by : Susann Stanley. Provided by : Vimeo. Located at : https://vimeo.com/35754924 . License : All Rights Reserved

6.2 Classical Conditioning

Learning objectives.

By the end of this section, you will be able to:

• Explain how classical conditioning occurs
• Summarize the processes of acquisition, extinction, spontaneous recovery, generalization, and discrimination

Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you have heard of Pavlov and his famous dogs.

Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his experiments in classical conditioning ( Figure 6.3 ). As we discussed briefly in the previous section, classical conditioning is a process by which we learn to associate stimuli and, consequently, to anticipate events.

Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist, not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). In his studies with dogs, Pavlov measured the amount of saliva produced in response to various foods. Over time, Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food, at the sight of an empty food bowl, and even at the sound of the laboratory assistants' footsteps. Salivating to food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of an empty bowl or the sound of footsteps.

These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs' “psychic secretions” (Pavlov, 1927). To explore this phenomenon in an objective manner, Pavlov designed a series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a bell, a light, and a touch on the leg. Through his experiments, Pavlov realized that an organism has two types of responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned (learned) responses.

In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder in this situation was an unconditioned stimulus (UCS) : a stimulus that elicits a reflexive response in an organism. The dogs’ salivation was an unconditioned response (UCR) : a natural (unlearned) reaction to a given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:

In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus. Pavlov would sound a tone (like ringing a bell) and then give the dogs the meat powder ( Figure 6.4 ). The tone was the neutral stimulus (NS) , which is a stimulus that does not naturally elicit a response. Prior to conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for the dogs.

When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned stimulus (CS) , which is a stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the sound of the assistants’ footsteps. The behavior caused by the conditioned stimulus is called the conditioned response (CR) . In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they began to salivate (CR) in anticipation of food.

Link to Learning

View this video about Pavlov and his dogs to learn more.

Real World Application of Classical Conditioning

How does classical conditioning work in the real world? Consider the case of Moisha, who was diagnosed with cancer. When she received her first chemotherapy treatment, she vomited shortly after the chemicals were injected. In fact, every trip to the doctor for chemotherapy treatment shortly after the drugs were injected, she vomited. Moisha’s treatment was a success and her cancer went into remission. Now, when she visits her oncologist's office every 6 months for a check-up, she becomes nauseous. In this case, the chemotherapy drugs are the unconditioned stimulus (UCS), vomiting is the unconditioned response (UCR), the doctor’s office is the conditioned stimulus (CS) after being paired with the UCS, and nausea is the conditioned response (CR). Let's assume that the chemotherapy drugs that Moisha takes are given through a syringe injection. After entering the doctor's office, Moisha sees a syringe, and then gets her medication. In addition to the doctor's office, Moisha will learn to associate the syringe with the medication and will respond to syringes with nausea. This is an example of higher-order (or second-order) conditioning, when the conditioned stimulus (the doctor's office) serves to condition another stimulus (the syringe). It is hard to achieve anything above second-order conditioning. For example, if someone rang a bell every time Moisha received a syringe injection of chemotherapy drugs in the doctor's office, Moisha likely will never get sick in response to the bell.

Consider another example of classical conditioning. Let’s say you have a cat named Tiger, who is quite spoiled. You keep her food in a separate cabinet, and you also have a special electric can opener that you use only to open cans of cat food. For every meal, Tiger hears the distinctive sound of the electric can opener (“zzhzhz”) and then gets her food. Tiger quickly learns that when she hears “zzhzhz” she is about to get fed. What do you think Tiger does when she hears the electric can opener? She will likely get excited and run to where you are preparing her food. This is an example of classical conditioning. In this case, what are the UCS, CS, UCR, and CR?

What if the cabinet holding Tiger’s food becomes squeaky? In that case, Tiger hears “squeak” (the cabinet), “zzhzhz” (the electric can opener), and then she gets her food. Tiger will learn to get excited when she hears the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus (“zzhzhz”) is called higher-order conditioning , or second-order conditioning . This means you are using the conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet ( Figure 6.5 ). It is hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet (“squeak”), use the can opener (“zzhzhz”), and then feed Tiger, Tiger will likely never get excited when hearing the bell alone.

Everyday Connection

Classical conditioning at stingray city.

Kate and her spouse recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary stingrays have become accustomed to interacting with humans. About 40 years ago, people began to clean fish and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays would swim in to eat (unconditioned response) what the people threw into the water; this continued for years. By the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs. When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know that they will get to eat (conditioned response).

As soon as they reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped into the water with bags of squid, the stingrays’ favorite treat. The swarm of stingrays bumped and rubbed up against their legs like hungry cats ( Figure 6.6 ). Kate was able to feed, pet, and even kiss (for luck) these amazing creatures. Then all the squid was gone, and so were the stingrays.

Classical conditioning also applies to humans, even babies. For example, Elan buys formula in blue canisters for their six-month-old daughter, Angelina. Whenever Elan takes out a formula container, Angelina gets excited, tries to reach toward the food, and most likely salivates. Why does Angelina get excited when she sees the formula canister? What are the UCS, CS, UCR, and CR here?

So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set boundaries. In this example, the edge of the yard elicits fear and anxiety in the dog. Fear and anxiety are the conditioned response.

Watch this video clip from the television show, The Office , for a humorous look at conditioning in which Jim conditions Dwight to expect a breath mint every time Jim’s computer makes a specific sound.

General Processes in Classical Conditioning

Now that you know how classical conditioning works and have seen several examples, let’s take a look at some of the general processes involved. In classical conditioning, the initial period of learning is known as acquisition , when an organism learns to connect a neutral stimulus and an unconditioned stimulus. During acquisition, the neutral stimulus begins to elicit the conditioned response, and eventually the neutral stimulus becomes a conditioned stimulus capable of eliciting the conditioned response by itself. Timing is important for conditioning to occur. Typically, there should only be a brief interval between presentation of the conditioned stimulus and the unconditioned stimulus. Depending on what is being conditioned, sometimes this interval is as little as five seconds (Chance, 2009). However, with other types of conditioning, the interval can be up to several hours.

Taste aversion is a type of conditioning in which an interval of several hours may pass between the conditioned stimulus (something ingested) and the unconditioned stimulus (nausea or illness). Here’s an example. Harry went to the carnival. He ate a lot of cotton candy and later that night was very sick and threw up. The next day, his friend offered him a piece of candy. He put it into his mouth and started to feel sick and had to spit it out. The unconditioned stimulus is eating too much cotton candy. The unconditioned response is getting sick and throwing up. The conditioned stimulus is the sugary flavor and the conditioned response is Harry feeling nauseous at the taste of sugar.

How does this occur—conditioning based on a single instance and involving an extended time lapse between the event and the negative stimulus? Research into taste aversion suggests that this response may be an evolutionary adaptation designed to help organisms quickly learn to avoid harmful foods (Garcia & Rusiniak, 1980; Garcia & Koelling, 1966). Not only may this contribute to species survival via natural selection, but it may also help us develop strategies for challenges such as helping cancer patients through the nausea induced by certain treatments (Holmes, 1993; Jacobsen et al., 1993; Hutton, Baracos, & Wismer, 2007; Skolin et al., 2006). Garcia and Koelling (1966) showed not only that taste aversions could be conditioned, but also that there were biological constraints to learning. In their study, separate groups of rats were conditioned to associate either a flavor with illness, or lights and sounds with illness. Results showed that all rats exposed to flavor-illness pairings learned to avoid the flavor, but none of the rats exposed to lights and sounds with illness learned to avoid lights or sounds. This added evidence to the idea that classical conditioning could contribute to species survival by helping organisms learn to avoid stimuli that posed real dangers to health and welfare.

Robert Rescorla demonstrated how powerfully an organism can learn to predict the UCS from the CS. Take, for example, the following two situations. Ari’s dad always has dinner on the table every day at 6:00. Soraya’s mom switches it up so that some days they eat dinner at 6:00, some days they eat at 5:00, and other days they eat at 7:00. For Ari, 6:00 reliably and consistently predicts dinner, so Ari will likely start feeling hungry every day right before 6:00, even if he's had a late snack. Soraya, on the other hand, will be less likely to associate 6:00 with dinner, since 6:00 does not always predict that dinner is coming. Rescorla, along with his colleague at Yale University, Allan Wagner, developed a mathematical formula that could be used to calculate the probability that an association would be learned given the ability of a conditioned stimulus to predict the occurrence of an unconditioned stimulus and other factors; today this is known as the Rescorla-Wagner model (Rescorla & Wagner, 1972)

Once we have established the connection between the unconditioned stimulus and the conditioned stimulus, how do we break that connection and get the dog, cat, or child to stop responding? In Tiger’s case, imagine what would happen if you stopped using the electric can opener for her food and began to use it only for human food. Now, Tiger would hear the can opener, but she would not get food. In classical conditioning terms, you would be giving the conditioned stimulus, but not the unconditioned stimulus. Pavlov explored this scenario in his experiments with dogs: sounding the tone without giving the dogs the meat powder. Soon the dogs stopped responding to the tone. Extinction is the decrease in the conditioned response when the unconditioned stimulus is no longer presented with the conditioned stimulus. When presented with the conditioned stimulus alone, the dog, cat, or other organism would show a weaker and weaker response, and finally no response. In classical conditioning terms, there is a gradual weakening and disappearance of the conditioned response.

What happens when learning is not used for a while—when what was learned lies dormant? As we just discussed, Pavlov found that when he repeatedly presented the bell (conditioned stimulus) without the meat powder (unconditioned stimulus), extinction occurred; the dogs stopped salivating to the bell. However, after a couple of hours of resting from this extinction training, the dogs again began to salivate when Pavlov rang the bell. What do you think would happen with Tiger’s behavior if your electric can opener broke, and you did not use it for several months? When you finally got it fixed and started using it to open Tiger’s food again, Tiger would remember the association between the can opener and her food—she would get excited and run to the kitchen when she heard the sound. The behavior of Pavlov’s dogs and Tiger illustrates a concept Pavlov called spontaneous recovery : the return of a previously extinguished conditioned response following a rest period ( Figure 6.7 ).

Of course, these processes also apply in humans. For example, let’s say that every day when you walk to campus, an ice cream truck passes your route. Day after day, you hear the truck’s music (neutral stimulus), so you finally stop and purchase a chocolate ice cream bar. You take a bite (unconditioned stimulus) and then your mouth waters (unconditioned response). This initial period of learning is known as acquisition, when you begin to connect the neutral stimulus (the sound of the truck) and the unconditioned stimulus (the taste of the chocolate ice cream in your mouth). During acquisition, the conditioned response gets stronger and stronger through repeated pairings of the conditioned stimulus and unconditioned stimulus. Several days (and ice cream bars) later, you notice that your mouth begins to water (conditioned response) as soon as you hear the truck’s musical jingle—even before you bite into the ice cream bar. Then one day you head down the street. You hear the truck’s music (conditioned stimulus), and your mouth waters (conditioned response). However, when you get to the truck, you discover that they are all out of ice cream. You leave disappointed. The next few days you pass by the truck and hear the music, but don’t stop to get an ice cream bar because you’re running late for class. You begin to salivate less and less when you hear the music, until by the end of the week, your mouth no longer waters when you hear the tune. This illustrates extinction. The conditioned response weakens when only the conditioned stimulus (the sound of the truck) is presented, without being followed by the unconditioned stimulus (chocolate ice cream in the mouth). Then the weekend comes. You don’t have to go to class, so you don’t pass the truck. Monday morning arrives and you take your usual route to campus. You round the corner and hear the truck again. What do you think happens? Your mouth begins to water again. Why? After a break from conditioning, the conditioned response reappears, which indicates spontaneous recovery.

Acquisition and extinction involve the strengthening and weakening, respectively, of a learned association. Two other learning processes—stimulus discrimination and stimulus generalization—are involved in determining which stimuli will trigger learned responses. Animals (including humans) need to distinguish between stimuli—for example, between sounds that predict a threatening event and sounds that do not—so that they can respond appropriately (such as running away if the sound is threatening). When an organism learns to respond differently to various stimuli that are similar, it is called stimulus discrimination . In classical conditioning terms, the organism demonstrates the conditioned response only to the conditioned stimulus. Pavlov’s dogs discriminated between the basic tone that sounded before they were fed and other tones (e.g., the doorbell), because the other sounds did not predict the arrival of food. Similarly, Tiger, the cat, discriminated between the sound of the can opener and the sound of the electric mixer. When the electric mixer is going, Tiger is not about to be fed, so she does not come running to the kitchen looking for food. In our other example, Moisha, the cancer patient, discriminated between oncologists and other types of doctors. She learned not to feel ill when visiting doctors for other types of appointments, such as her annual physical.

On the other hand, when an organism demonstrates the conditioned response to stimuli that are similar to the condition stimulus, it is called stimulus generalization , the opposite of stimulus discrimination. The more similar a stimulus is to the condition stimulus, the more likely the organism is to give the conditioned response. For instance, if the electric mixer sounds very similar to the electric can opener, Tiger may come running after hearing its sound. But if you do not feed her following the electric mixer sound, and you continue to feed her consistently after the electric can opener sound, she will quickly learn to discriminate between the two sounds (provided they are sufficiently dissimilar that she can tell them apart). In our other example, Moisha continued to feel ill whenever visiting other oncologists or other doctors in the same building as her oncologist.

Behaviorism

John B. Watson , shown in Figure 6.8 , is considered the founder of behaviorism. Behaviorism is a school of thought that arose during the first part of the 20th century, which incorporates elements of Pavlov’s classical conditioning (Hunt, 2007). In stark contrast with Freud, who considered the reasons for behavior to be hidden in the unconscious, Watson championed the idea that all behavior can be studied as a simple stimulus-response reaction, without regard for internal processes. Watson argued that in order for psychology to become a legitimate science, it must shift its concern away from internal mental processes because mental processes cannot be seen or measured. Instead, he asserted that psychology must focus on outward observable behavior that can be measured.

Watson’s ideas were influenced by Pavlov’s work. According to Watson, human behavior, just like animal behavior, is primarily the result of conditioned responses. Whereas Pavlov’s work with dogs involved the conditioning of reflexes, Watson believed the same principles could be extended to the conditioning of human emotions (Watson, 1919).

In 1920, while chair of the psychology department at Johns Hopkins University, Watson and his graduate student, Rosalie Rayner, conducted research on a baby nicknamed Little Albert. Rayner and Watson’s experiments with Little Albert demonstrated how fears can be conditioned using classical conditioning. Through these experiments, Little Albert was exposed to and conditioned to fear certain things. Initially he was presented with various neutral stimuli, including a rabbit, a dog, a monkey, masks, cotton wool, and a white rat. He was not afraid of any of these things. Then Watson, with the help of Rayner, conditioned Little Albert to associate these stimuli with an emotion—fear. For example, Watson handed Little Albert the white rat, and Little Albert enjoyed playing with it. Then Watson made a loud sound, by striking a hammer against a metal bar hanging behind Little Albert’s head, each time Little Albert touched the rat. Little Albert was frightened by the sound—demonstrating a reflexive fear of sudden loud noises—and began to cry. Watson repeatedly paired the loud sound with the white rat. Soon Little Albert became frightened by the white rat alone. In this case, what are the UCS, CS, UCR, and CR? Days later, Little Albert demonstrated stimulus generalization—he became afraid of other furry things: a rabbit, a furry coat, and even a Santa Claus mask ( Figure 6.9 ). Watson had succeeded in conditioning a fear response in Little Albert, thus demonstrating that emotions could become conditioned responses. It had been Watson’s intention to produce a phobia—a persistent, excessive fear of a specific object or situation— through conditioning alone, thus countering Freud’s view that phobias are caused by deep, hidden conflicts in the mind. However, there is no evidence that Little Albert experienced phobias in later years. While Watson’s research provided new insight into conditioning, it would be considered unethical by today’s standards.

View scenes from this video on John Watson’s experiment in which Little Albert was conditioned to respond in fear to furry objects to learn more.

As you watch the video, look closely at Little Albert’s reactions and the manner in which Watson and Rayner present the stimuli before and after conditioning. Based on what you see, would you come to the same conclusions as the researchers?

Advertising and Associative Learning

Advertising executives are pros at applying the principles of associative learning. Think about the car commercials you have seen on television. Many of them feature an attractive model. By associating the model with the car being advertised, you come to see the car as being desirable (Cialdini, 2008). You may be asking yourself, does this advertising technique actually work? According to Cialdini (2008), men who viewed a car commercial that included an attractive model later rated the car as being faster, more appealing, and better designed than did men who viewed an advertisement for the same car minus the model.

Have you ever noticed how quickly advertisers cancel contracts with a famous athlete following a scandal? As far as the advertiser is concerned, that athlete is no longer associated with positive feelings; therefore, the athlete cannot be used as an unconditioned stimulus to condition the public to associate positive feelings (the unconditioned response) with their product (the conditioned stimulus).

Now that you are aware of how associative learning works, see if you can find examples of these types of advertisements on television, in magazines, or on the Internet.

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• Mental Health

Classical Conditioning: How It Works and Examples

What Is Classical Conditioning?

Classical conditioning, also called Pavlovian conditioning or respondent conditioning, is learning through association. This behavioral learning method was first studied in the late 19th century by Russian physiologist Ivan Pavlov. 

Pavlov’s dog experiment

In the 1890s, Pavlov was experimenting with dogs, ringing a bell whenever they were fed. Over time, the dogs learned to associate a neutral stimulus (bell ringing) with a positive one (food). Pavlov also noticed that his dogs would often begin to salivate whenever they heard the footsteps of his assistant bringing them the food. This is called a conditioned response. Pavlov's experiment and its association between positive and neutral stimuli became the foundation of classical conditioning theory.

Eventually, Pavlov linked these behavioral associations to humans. He spent the remainder of his career studying the phenomenon.

Terms to Know

To understand how classical conditioning works, it's helpful to understand the following terms.

• Neutral stimulus. A stimulus is something that triggers a physical or behavioral change. A neutral stimulus produces no response. At first, Pavlov's dogs had no response to the bell.
• Unconditioned stimulus. This is what leads to an automatic response. In Pavlov’s experiment, it's the food.
• Unconditioned response . A normal process, like salivating when you smell food, is an unconditioned response.
• Conditioned stimulus. This is when a formerly neutral stimulus, like the bell in Pavlov's experiment, mimics an unconditioned response, as when the dogs began to associate the bell with food and salivate.
• Conditioned response. The learned behavior, such as relating the bell to food, is called a conditioned response.  

What Is Classical Conditioning Theory?

Classical conditioning theory says that behaviors are learned by connecting a neutral stimulus with a positive one, such as when Pavlov's dogs heard a bell (neutral) and expected food (positive).  

There are essentially three stages in classical conditioning:.

Before conditioning. Something in the environment triggers a natural response in the subject. During this stage, no new behavior has been learned yet. This stage also includes a neutral stimulus, which doesn't affect the subject. To create a response to a neutral stimulus, it must be linked to an unconditioned stimulus -- like the bell to food. 

During conditioning. This is the stage in which the subject starts to associate the neutral stimulus with the positive stimulus that caused the response during the first stage. In Pavlov's experiment, this stage involved ringing a bell when the dogs were fed. Over time, the dogs began to associate the bell with food.

For this to work, the neutral stimulus should come before the positive (unconditioned) stimulus. It creates a cue for what comes next. Doing this over and over makes the conditioning stick. But sometimes it only takes one time to make an association, such as a hangover after too much drinking. 

After conditioning. During the final stage of conditioning, the subject firmly associates the neutral stimulus with the unconditioned response. This creates a new behavior, or what's known as the conditioned response. If the link between the two weakens or breaks, this leads to what's called extinction. When Pavlov's dogs no longer got food after hearing the bell, they eventually stopped associating the bell with food.

What Is the Little Albert Experiment?

Considered one of the "most ethically dubious experiments ever conducted," the Little Albert experiment was developed by psychologists John B. Watson and Rosalie Rayner, who first applied Pavlov's classical conditioning principles to human behavior.

In 1920, Watson and Rayner began their behavioral learning experiment with a 9-month-old boy named Albert. They tested his reactions to various things in his environment, including a white rat, burning newspapers, and a hammer striking a 4-foot steel bar just behind Albert's head. Because the sound of the hammer frightened Albert, it became the unconditioned stimulus, and fear became the unconditioned response.

When Albert was 11 months old, he was presented with the white rat. When he tried to pet it, the pipe was struck with the hammer, causing him to feel fear. The researchers did this over the next few weeks and eventually Albert saw the rat and showed a fearful response. 

They reproduced these results with a rabbit, a dog, and several other stimuli that were previously neutral. At the end of the experiment, Albert showed a fear response for all of them.

Classical Conditioning vs. Operant Conditioning

Classical conditioning relies on associating one stimulus with another, such as the sound of a bell with food. Learning through operant conditioning relies on what comes after behaviors. These are the consequences that reinforce or punish behaviors.

In operant conditioning, either positive or negative reinforcement is used to affect whether a behavior is likely to happen again.  

When you give your dog a treat after they follow a command, that's positive reinforcement. It encourages them to repeat the behavior. When you yell (punishment) after your dog grabs food off the counter, that's punishment or negative reinforcement. Like classical conditioning, operant conditioning requires repetition for learning to take place. 

Classical Conditioning Principles

Classical conditioning includes several steps:

Acquisition. The point at which the neutral stimulus and unconditioned stimulus become linked. In other words, the dog learns to relate the sound of the bell with food.  

Extinction. Extinction breaks the conditioned bonds between the stimuli. If the dog no longer sees food after hearing the bell, it will gradually stop associating the bell with food.

Spontaneous recovery. If, after extinction, the conditioned stimulus and neutral stimulus again appear in relationship to one another, the conditioned response will return. After the extinction of the conditioned response in his dogs, Pavlov rang the bell before producing the food a few days later. His dogs began to salivate at the sound of the bell again.

Generalization. A conditioned response may be produced with stimuli that are similar but not the same. For example, if Pavlov's dogs heard a bell that rang at a lower pitch and still salivated, that's generalization.

Discrimination. Discrimination is the ability to understand that two or more stimuli are different from one another. In Pavlov's experiment, he later introduced the dogs to two bell sounds. Food appeared only after one. The dogs soon learned the difference. 

Classical Conditioning Examples

Classical conditioning isn't just related to food or fear. You see examples of this type of conditioning every day, though you may not know it or consciously think about it. Here are some examples of classical conditioning in daily life.

• Every time you put on your shoes, your dog gets excited and runs to the front door. Your dog associates you putting on shoes with a walk, or maybe going for a car ride.
• You always buy the same type of crackers for your baby's morning snack. When you pull the box of crackers out of the cupboard, your baby gets excited and reaches toward the box because they associate that box with snack time.
• A certain perfume reminds you of your late grandmother. After her passing, smelling that perfume or similar scents make you sad because of its association with your grandmother.
• Your demanding boss occasionally berates underperforming employees in his office. You feel nervous or agitated whenever your boss asks one of your co-workers into his office and closes the door because that's what he does whenever someone's in trouble.
• You listen to your favorite music when you exercise. You don't generally enjoy working out, but eventually, you begin to relate the positive feelings you get from your playlist to working out.
• Advertising. You see an ad showing a cold, wet can of soda while pumping your gas. You start feeling thirsty and think about running inside and buying this soft drink. 

Classical Conditioning Uses

Psychologists consider classical conditioning a key type of learning. It can create changes in mental and physical health, emotions, and drive. Its uses include: 

• Phobias. Repeated exposure to the object of a phobia, such as frequently flying when you're afraid of planes, can reduce fears.
• Drug use. Counselors often urge former addicts to stay away from people and places associated with their drug use.
• Classroom learning. Teachers might use classical conditioning to associate learning with positive emotions rather than negative ones like fear or shame.
• Pet training. Classical conditioning taught Pavlov's dogs what to expect after they heard the bell: food. Your dog also learns to positively associate actions like picking up a leash with going for a walk or going out to pee.
• Food aversions. We're born favoring certain tastes more than others (like sweet vs. bitter). If you eat something and become sick, you might learn to avoid the food and even feel sick at the sight of it. 
• PTSD  For people with posttraumatic stress disorder (PTSD) , classical conditioning may not cure their condition but contribute to it. PTSD is a type of anxiety that comes from associating certain triggers with fearful experiences. For example, loud noises may remind a veteran of the sounds of war. 

Criticisms of Classical Conditioning

Classical conditioning stresses outward learning over traits we're born with. Some criticisms of classical conditioning include:

• It fails to consider complex human actions like thinking, reason, and memory that produce learning, too. 
• It takes a long time to make the associations that create learning.
• It assumes a lack of free will -- that people have no control over their reactions to stimuli.

Classical conditioning is a type of learning by association. It takes several steps to associate a neutral stimulus with a positive outcome. Classical conditioning is used to treat psychological problems such as drug addiction and phobias. But it's also the basis for posttraumatic stress disorder (PTSD). Classical conditioning appears in everyday life in advertising and in our sensory associations with good and bad events. 

Classical Conditioning FAQs

• What is the simple definition of classical conditioning? Classical conditioning is learning through association.  
• What is an example of classical conditioning? Listening to your favorite music during workouts is an example of associating exercise with a positive neutral stimulus.  
• What are the five elements of classical conditioning?  Elements of classical conditioning include acquisition, extinction, spontaneous recovery, generalization, and discrimination.

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Chapter 8. Learning

Classical Conditioning

Dinesh Ramoo

Approximate reading time: 28 minutes

Learning Objectives

By the end of this section, you will be able to:

• Explain how classical conditioning occurs
• Summarise the processes of acquisition, extinction, spontaneous recovery, generalisation, and discrimination

Ivan Pavlov

Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you have heard of Pavlov and his famous dogs.

Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his experiments in classical conditioning (Figure L.3). As we discussed briefly in the previous section, classical conditioning is a process by which we learn to associate stimuli with results and, consequently, to anticipate events.

Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist, not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). He was the first Russian to win the Nobel Prize for his contributions to medicine. In his studies with dogs, Pavlov measured the amount of saliva produced in response to various foods. Over time, Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food, at the sight of an empty food bowl, and even at the sound of the laboratory assistants’ footsteps. Salivating to food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of an empty bowl or the sound of footsteps.

These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs’ “psychic secretions” (Pavlov, 1927). To explore this phenomenon objectively, Pavlov designed a series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a bell, a light, and a touch on the leg. Through his experiments, Pavlov realised that an organism has two types of responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned (learned) responses.

In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder in this situation was an unconditioned stimulus (US): a stimulus that elicits a reflexive response in an organism. The dogs’ salivation was an unconditioned response (UCR): a natural (unlearned) reaction to a given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:

Meat powder (US) → Salivation (UCR)

In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus. Pavlov would sound a tone (like a bell ringing) and then give the dogs the meat powder (Figure L.4). The tone was the neutral stimulus (NS), which is a stimulus that does not naturally elicit a response. Prior to conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for the dogs.

Tone (NS) + Meat Powder (US) → Salivation (UCR)

When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned stimulus (CS), which is a stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the sound of the assistants’ footsteps. The behaviour caused by the conditioned stimulus is called the conditioned response (CR). In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they began to salivate (CR) in anticipation of food.

View this video about Pavlov and his dogs to learn more: Pavlov’s Classical Conditioning (6 minutes)

“Pavlov’s Classical Conditioning” video by Sprouts is licensed under the Standard YouTube licence.

Real World Application of Classical Conditioning

How does classical conditioning work in the real world?

Let’s say you have a cat named Zelda, who is quite spoiled. You keep Zelda’s food in a separate cabinet, and you also have a special electric can opener that you use only to open cans of cat food. For every meal, Zelda hears the distinctive sound of the electric can opener (“zzhzhz”) and then gets her food. Zelda quickly learns that when she hears “zzhzhz” that means it’s feeding time. What do you think Zelda does when she hears the electric can opener? Zelda will likely get excited and run to where you are preparing their food. This is an example of classical conditioning. In this case, what are the US, CS, UCR, and CR?

What if the cabinet holding Zelda’s food becomes squeaky? In that case, Zelda hears “squeak” (the cabinet), “zzhzhz” (the electric can opener), and then she gets the food. Zelda will learn to get excited when she hears the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus (“zzhzhz”) is called higher-order conditioning , or second-order conditioning . This means you are using the conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet (Figure L.5). It is hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet (“squeak”), use the can opener (“zzhzhz”), and then feed Zelda, Zelda will likely never get excited when hearing the bell alone.

Now consider the case of Farah, who was diagnosed with cancer. When Farah received their first chemotherapy treatment, they vomited shortly after the chemicals were injected. In fact, on every trip to the doctor for chemotherapy treatment, shortly after the drugs were injected, Farah vomited. Farah’s treatment was a success and their cancer went into remission. Now, when Farah visits their oncologist’s office every 6 months for a check-up, they become nauseous. In this case, the chemotherapy drugs are the unconditioned stimulus (US), vomiting is the unconditioned response (UCR), the doctor’s office is the conditioned stimulus (CS) after being paired with the US, and nausea is the conditioned response (CR). Let’s assume that the chemotherapy drugs that Farah takes are given through a syringe injection. After entering the doctor’s office, Farah sees a syringe, and then gets their medication. In addition to the doctor’s office, Farah will learn to associate the syringe with the medication and will respond to syringes with nausea. This is an example of higher-order (or second-order) conditioning, when the conditioned stimulus (the doctor’s office) serves to condition another stimulus (the syringe). Because it is hard to achieve anything above second-order conditioning, if someone rang a bell, for example, every time Farah received a syringe injection of chemotherapy drugs in the doctor’s office, Farah likely would not get sick in response to the bell.

Classical conditioning  even applies to babies. For example, Logan buys formula in blue canisters for their six-month-old baby, Reagan. Whenever Logan takes out a formula container, Reagan gets excited, tries to reach toward the food, and most likely salivates. Why does Reagan get excited when they see the formula canister? What are the US, CS, UCR, and CR here?

So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set boundaries. In this example, the edge of the yard elicits fear and anxiety in the dog. Fear and anxiety are the conditioned response.

Everyday Connection: Classical Conditioning at Stingray City

Kate and her spouse recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary stingrays have become accustomed to interacting with humans. About 40 years ago, fishermen began to clean fish and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays would swim in to eat (unconditioned response) what the fishermen threw into the water; this continued for years. By the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs. When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know that they will get to eat (conditioned response).

As soon as they reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped into the water with bags of squid, the stingrays’ favourite treat.

The swarm of stingrays bumped and rubbed up against their legs like hungry cats (Figure L.6). Kate was able to feed, pet, and even kiss (for luck) these amazing creatures. Then all the squid was gone, and so were the stingrays.

General Processes in Classical Conditioning

Acquisition.

Now that you know how classical conditioning works and have seen several examples, let’s take a look at some of the general processes involved. In classical conditioning, the initial period of learning is known as acquisition , when an organism learns to connect a neutral stimulus and an unconditioned stimulus. During acquisition, the neutral stimulus begins to elicit the conditioned response, and eventually the neutral stimulus becomes a conditioned stimulus capable of eliciting the conditioned response by itself. Timing is important for conditioning to occur. Typically, there should be only a brief interval between presentation of the conditioned stimulus and the unconditioned stimulus. Depending on what is being conditioned, sometimes this interval is as little as five seconds (Chance, 2009). However, with other types of conditioning, the interval can be up to several hours.

Taste aversion is a type of conditioning in which an interval of several hours may pass between the conditioned stimulus (something ingested) and the unconditioned stimulus (nausea or illness). Here’s how it works. Between classes, you and a friend grab a quick lunch from a food cart on campus. You share a dish of chicken curry and head off to your next class. A few hours later, you feel nauseous and become ill. Although your friend is fine and you determine that you have intestinal flu (the food is not the culprit), you’ve developed a taste aversion; the next time you are at a restaurant and someone orders curry, you immediately feel ill. While the chicken dish is not what made you sick, you are experiencing taste aversion: you’ve been conditioned to be averse to a food after a single, bad experience.

How does conditioning occur based on a single instance and involving an extended time lapse between the event and the negative stimulus? Research into taste aversion suggests that this response may be an evolutionary adaptation designed to help organisms quickly learn to avoid harmful foods (Garcia & Rusiniak, 1980; Garcia & Koelling, 1966). Not only may this contribute to species survival via natural selection, but it may also help us develop strategies for challenges, such as helping cancer patients through the nausea induced by certain treatments (Holmes, 1993; Jacobsen et al., 1993; Hutton, Baracos, & Wismer, 2007; Skolin et al., 2006). But why would a person develop an aversion to the taste or smell of a food rather than to all the other stimuli that accompanied the food? Why not the cutlery or the music that was playing at the time?

Garcia and Koelling (1966) showed not only that taste aversions could be conditioned, but also that there were biological constraints to learning. In their study, separate groups of rats were conditioned to associate either a flavour with illness, or lights and sounds with illness. Results showed that all rats exposed to flavour-illness pairings learned to avoid the flavour, but none of the rats exposed to lights and sounds with illness learned to avoid lights or sounds. This added evidence to the idea that classical conditioning could contribute to species survival by helping organisms learn to avoid stimuli that posed real dangers to health and welfare.

Robert Rescorla demonstrated how powerfully an organism can learn to predict the US from the CS. Take, for example, the following two situations. Tafadawa’s family always has dinner on the table every day at 6:00. Hai’s family switches it up so that some days they eat dinner at 6:00, some days they eat at 5:00, and other days they eat at 7:00. For Tafadawa, 6:00 reliably and consistently predicts dinner, so Tafadawa will likely start feeling hungry every day right before 6:00, even if he’s had a late snack. Hai, on the other hand, will be less likely to associate 6:00 with dinner, since 6:00 does not always predict that dinner is coming. Rescorla, along with his colleague at Yale University, Alan Wagner, developed a mathematical formula that could be used to calculate the probability that an association would be learned given the ability of a conditioned stimulus to predict the occurrence of an unconditioned stimulus and other factors; today this is known as the Rescorla-Wagner model (Rescorla & Wagner, 1972). We also know that conditioning can be unrelated to food. It can also trigger an emotional response, rather than a physical one. For example, if an experimenter sounds a tone just before applying a mild shock to a rat’s feet, the tone will elicit fear or anxiety after one or two pairings. Similar fear conditioning plays a role in creating many anxiety disorders in humans, such as phobias and panic disorders, where people associate cues (such as closed spaces, or a shopping mall) with panic or other emotional trauma. Here, rather than a physical response (like drooling), the CS triggers an emotion.

Once we have established the connection between the unconditioned stimulus and the conditioned stimulus, how do we break that connection and get the dog, cat, or child to stop responding? In Zelda’s case, imagine what would happen if you stopped using the electric can opener for her food and began to use it only for human food. Now, Zelda would hear the can opener, but she would not get food. In classical conditioning terms, you would be giving the conditioned stimulus, but not the unconditioned stimulus. Pavlov explored this scenario in his experiments with dogs: sounding the tone without giving the dogs the meat powder. Soon the dogs stopped responding to the tone. Extinction is the decrease in the conditioned response when the unconditioned stimulus is no longer presented with the conditioned stimulus. When presented with the conditioned stimulus alone, the dog, cat, or other organism would show a weaker and weaker response, and finally no response. In classical conditioning terms, there is a gradual weakening and disappearance of the conditioned response.

What happens when learning is not used for a while—when what was learned lies dormant? As we just discussed, Pavlov found that when he repeatedly presented the bell (conditioned stimulus) without the meat powder (unconditioned stimulus), extinction occurred; the dogs stopped salivating to the bell. However, after a couple of hours of resting from this extinction training, the dogs again began to salivate when Pavlov rang the bell. What do you think would happen with Zelda’s behaviour if your electric can opener broke, and you did not use it for several months? When you finally got it fixed and started using it to open Zelda’s food again, Zelda would remember the association between the can opener and food—she  would get excited and run to the kitchen when she heard the sound. The behaviour of Pavlov’s dogs and Zelda illustrates a concept Pavlov called spontaneous recovery : the return of a previously extinguished conditioned response following a rest period (Figure L.7).

Of course, these processes also apply in humans. For example, let’s say that every day when you walk to campus, an ice cream truck passes your route. Day after day, you hear the truck’s music (neutral stimulus), so you finally stop and purchase a chocolate ice cream bar. You take a bite (unconditioned stimulus) and then your mouth waters (unconditioned response). This initial period of learning is known as acquisition, when you begin to connect the neutral stimulus (the sound of the truck) and the unconditioned stimulus (the taste of the chocolate ice cream in your mouth). During acquisition, the conditioned response gets stronger and stronger through repeated pairings of the conditioned stimulus and unconditioned stimulus. Several days (and ice cream bars) later, you notice that your mouth begins to water (conditioned response) as soon as you hear the truck’s musical jingle—even before you bite into the ice cream bar. Then one day you head down the street. You hear the truck’s music (conditioned stimulus), and your mouth waters (conditioned response). However, when you get to the truck, you discover that they are all out of ice cream. You leave disappointed. The next few days you pass by the truck and hear the music, but don’t stop to get an ice cream bar because you’re running late for class. You begin to salivate less and less when you hear the music, until by the end of the week, your mouth no longer waters when you hear the tune. This illustrates extinction. The conditioned response weakens when only the conditioned stimulus (the sound of the truck) is presented, without being followed by the unconditioned stimulus (chocolate ice cream in the mouth). Then the weekend comes. You don’t have to go to class, so you don’t pass the truck. Monday morning arrives and you take your usual route to campus. You round the corner and hear the truck again. What do you think happens? Your mouth begins to water again. Why? After a break from conditioning, the conditioned response reappears, which indicates spontaneous recovery.

Acquisition and extinction involve the strengthening and weakening, respectively, of a learned association. Two other learning processes— stimulus discrimination and stimulus generalisation—are involved in determining which stimuli will trigger learned responses. Animals (including humans) need to distinguish between stimuli—for example, between sounds that predict a threatening event and sounds that do not—so that they can respond appropriately (such as running away if the sound is threatening). When an organism learns to respond differently to various stimuli that are similar, it is called stimulus discrimination. In classical conditioning terms, the organism demonstrates the conditioned response only to the conditioned stimulus. Pavlov’s dogs discriminated between the basic tone that sounded before they were fed and other tones (e.g., the doorbell) because the other sounds did not predict the arrival of food. Similarly, Zelda, the cat, discriminated between the sound of the can opener and the sound of the electric mixer. When the electric mixer is going, Zelda is not about to be fed, so she does  not come running to the kitchen looking for food. In our other example, Farah, the cancer patient, discriminated between oncologists and other types of doctors. Farah learned not to feel ill when visiting doctors for other types of appointments, such as their annual physical.

On the other hand, when an organism demonstrates the conditioned response to stimuli that are similar to the condition stimulus, it is called stimulus generalisation , the opposite of stimulus discrimination. The more similar a stimulus is to the condition stimulus, the more likely the organism is to give the conditioned response. For instance, if the electric mixer sounds very similar to the electric can opener, Zelda may come running after hearing its sound. But if you do not feed Zelda following the electric mixer sound, and you continue to feed her consistently after the electric can opener sound, Zelda will quickly learn to discriminate between the two sounds (provided they are sufficiently dissimilar that she can tell them apart). In our other example, Farah continued to feel ill whenever visiting other oncologists or other doctors in the same building as their oncologist.

Behaviourism

John B. Watson, shown in Figure L.8, is considered the founder of behaviourism. Behaviourism is a school of thought that arose during the first part of the 20th century, incorporating elements of Pavlov’s classical conditioning (Hunt, 2007). In many ways, behaviourism arose as a response to what many saw as the unscientific, even mystical direction that psychology was taking in the early 20th century. Psychoanalysis postulated quite a few unfalsifiable and unquantifiable entities such as the unconscious, impulses, the ego, and the id, among others. Psychologists were being presented with conclusions from case studies done by Freud and his colleagues as evidence but there was no way to replicate those findings. In stark contrast with Freud, who considered the reasons for behaviour to be hidden in the unconscious, Watson championed the idea that all behaviour can be studied as a simple stimulus-response reaction, without regard for internal processes. Such processes were observable and measurable. The experiments could be replicated by other psychologists to test whether the postulates were universal. Watson argued that, in order for psychology to become a legitimate science, it must shift its concern away from internal mental processes because mental processes cannot be seen or measured. Instead, he asserted that psychology must focus on outward observable behaviour that can be measured.

Watson’s ideas were influenced by Pavlov’s work. According to Watson, human behaviour, just like animal behaviour, is primarily the result of conditioned responses. Whereas Pavlov’s work with dogs involved the conditioning of reflexes, Watson believed the same principles could be extended to the conditioning of human emotions (Watson, 1919). Thus began Watson’s work with his graduate student Rosalie Rayner and a baby called Little Albert. Through their experiments with Little Albert, Watson and Rayner (1920) demonstrated how fears can be conditioned.

In 1920, Watson was the chair of the psychology department at Johns Hopkins University. Through his position at the university he came to meet Little Albert’s mother, Arvilla Merritte, who worked at a campus hospital (DeAngelis, 2010). Watson offered her a dollar to allow her son to be the subject of his experiments in classical conditioning. Through these experiments, Little Albert was exposed to and conditioned to fear certain things. Initially he was presented with various neutral stimuli, including a rabbit, a dog, a monkey, masks, cotton wool, and a white rat. He was not afraid of any of these things. Then Watson, with the help of Rayner, conditioned Little Albert to associate these stimuli with an emotion—fear. For example, Watson handed Little Albert the white rat, and Little Albert enjoyed playing with it. Then Watson made a loud sound, by striking a hammer against a metal bar hanging behind Little Albert’s head, each time Little Albert touched the rat. Little Albert was frightened by the sound—demonstrating a reflexive fear of sudden loud noises—and began to cry. Watson repeatedly paired the loud sound with the white rat. Soon Little Albert became frightened by the white rat alone. In this case, what are the US, CS, UCR, and CR? Days later, Little Albert demonstrated stimulus generalisation—he became afraid of other furry things: a rabbit, a furry coat, and even a Santa Claus mask (Figure LE.9). Watson had succeeded in conditioning a fear response in Little Albert, thus demonstrating that emotions could become conditioned responses. It had been Watson’s intention to produce a phobia—a persistent, excessive fear of a specific object or situation— through conditioning alone, thus countering Freud’s view that phobias are caused by deep, hidden conflicts in the mind. However, there is no evidence that Little Albert experienced phobias in later years. Little Albert’s mother moved away, ending the experiment. While Watson’s research provided new insight into conditioning, it would be considered unethical by today’s standards.

View scenes from this video on John Watson’s experiment in which “Little Albert” was conditioned to respond in fear to furry objects, to learn more.

Watch this video: Baby Albert Experiments (3.5 minutes)

“ Baby Albert Experiments ” video by Jaap van der Steen is licensed under the Standard YouTube licence. The footage is in the public domain.

Image Attributions

Figure LE.3. “ Ivan Pavlov NLM3″  is in the public domain .

Figure LE.4. Figure 6.4 as found in Psychology 2e by OpenStax is licensed under a CC BY 4.0 License .

Figure LE.5. Figure 6.5 as found in Psychology 2e by OpenStax is licensed under a CC BY 4.0 License .

Figure LE.6. Figure 6.6 as found in Psychology 2e by OpenStax is licensed under a CC BY 4.0 License .

Figure LE.7. Figure 6.7 as found in Psychology 2e by OpenStax is licensed under a CC BY 4.0 License .

Figure LE.8. “John B. Watson” from the Johns Hopkins Gazette is in the public domain .

Figure LE.9. “ Little Albert ” from the Akron Psychology Archives is in the public domain .

To calculate this time, we used a reading speed of 150 words per minute and then added extra time to account for images and videos. This is just to give you a rough idea of the length of the chapter section. How long it will take you to engage with this chapter will vary greatly depending on all sorts of things (the complexity of the content, your ability to focus, etc).

learning in which the stimulus or experience occurs before the behaviour and then gets paired or associated with the behaviour

using a conditioned stimulus to condition a neutral stimulus

period of initial learning in classical conditioning in which a human or an animal begins to connect a neutral stimulus and an unconditioned stimulus so that the neutral stimulus will begin to elicit the conditioned response

a type of classical conditioning that elicits a fear response

decrease in the conditioned response when the unconditioned stimulus is no longer paired with the conditioned stimulus

return of a previously extinguished conditioned response

ability to respond differently to similar stimuli

demonstrating the conditioned response to stimuli that are similar to the conditioned stimulus

Classical Conditioning Copyright © 2024 by Dinesh Ramoo is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Classical Conditioning: Classical Yet Modern

This manuscript is part of a special issue to commemorate professor Paul Eelen, who passed away on August 21, 2016. Paul was a clinically oriented scientist, for whom learning principles (Pavlovian or operant) were more than salivary responses and lever presses. His expertise in learning psychology and his enthusiasm to translate this knowledge to clinical practice inspired many inside and outside academia. Several of his original writings were in the Dutch language. Instead of editing a special issue with contributions of colleagues and friends, we decided to translate a selection of his manuscripts to English to allow wide access to his original insights and opinions. Even though the manuscripts were written more than two decades ago, their content is surprisingly contemporary. The present manuscript was originally published as part of a Liber Amicorum for Paul Eelen’s own supervisor, prof. Joseph Nuttin. In this chapter, Paul Eelen presents a modern view on Pavlovian learning. It appeared in 1980, at the heyday of cognitive psychology which initially dismissed conditioning. Paul Eelen’s perseverance in presenting learning principles as key to study human behaviour has proven correct and ahead of time.

First published as: Eelen, P. (1980). Klassieke conditionering: Klassiek en toch modern. In Liber Amicorum, Prof. J. R. Nuttin, Gedrag, dynamische relatie en betekeniswereld (pp. 321–343). Leuven: Universitaire Pers Leuven.

Even though ever more complex areas of research have found their way into psychology, “Pavlov’s dog” continues to fascinate many researchers. What causes the enduring fascination with conditioning research? Does such research even have psychological significance? Would it not be better if it remained a study field for physiologists, as it originally was? The answers to these questions are partly determined by one’s conceptualization of classical conditioning. Most people are by now sufficiently familiar with its schematic representation: a conditioned stimulus (CS) elicits a conditioned response (CR), provided this stimulus has repeatedly been presented together with an unconditioned stimulus (US) that “inherently” elicits an unconditioned response (UR). Several limiting conditions qualify this schematic depiction. The CS must be “neutral” vis-à-vis the US. In other words, it cannot spontaneously elicit a response that is identical to the UR. The US must “inherently” elicit a well-defined response, which is why stimuli that are biologically significant for the studied organism are typically used (for some theorists, this became a necessary condition for conditioning to take place). The resulting CR must be an autonomous response that is part of the reaction pattern that the US evokes. This schematic depiction also provides insight into the necessary (and sufficient) conditions for conditioning to occur: both stimuli have to occur simultaneously. Finally, this schematic representation already implies what is learned: learning is equated with the modified reaction pattern vis-à-vis the CS. To put it simply, the dog learns to salivate at the sound of the bell.

This schematic depiction and the limiting conditions it implies constitute a strong simplification of the original phenomenon. After all, Pavlov’s interest in conditioning originated from his observation that the dog started to salivate when it heard and saw the man who brought the food. This rather complex event – someone who brings food – was ultimately reduced to a little lamp or an auditory signal predicting food. The “food” event of seeing a meat chunk in a bowl was reduced to the injection of meat powder directly into the animal’s mouth. The dog’s overall reaction pattern upon hearing the man who brings the food – and anyone who has a dog will be familiar with this pattern – was ultimately reduced to droplets of saliva (the reductive nature of this response was already highlighted by Zener, 1937 ). Moreover, the autonomous reaction that held Pavlov’s primary interest as a physiologist was initially not viewed as a core index of learning the relation between two events, but was subsequently seen as an almost integral part of the definition of classical conditioning ( Gormezano & Kehoe, 1975 ). We can probably all concur with Rescorla and Holland’s related observation that “if conditioning were confined to what some have called “spit and twitches”, it would lose much of its psychological interest” ( Rescorla & Holland, 1976, p. 184 ).

This strong reduction of the original events is probably characteristic of every type of operationalisation. This is justified in and of itself: operationalisations that reduce a phenomenon to its essence are vital for obtaining fundamental knowledge about the necessary and sufficient conditions that determine the occurrence of that phenomenon. But the danger exists that the question behind a concrete operationalisation is simply forgotten after a while. Moreover, there is a real danger that general statements and laws are formulated that are strongly connected to the concrete operationalisation. Something along those lines certainly happened in the study and appreciation of classical conditioning. The aim of this contribution, then, is to shed light on a number of recent trends in classical conditioning studies that might justify the title of this contribution. First, I summarize the most important findings that call for a broader framing of classical conditioning research. This is followed by a comprehensive discussion of one particular form of learning, that is, taste aversion that results from relations between the taste of food or drink on the one hand, and artificially induced nausea on the other hand. This phenomenon is sometimes referred to as the Garcia effect. The topic of taste aversion is discussed not because it is an almost prototypical example of classical conditioning, but because it contributed substantially to the questioning of important assumptions about conditioning. A number of authors have even called this the beginning of a “paradigmatic revolution” ( Rozin, 1977 ; Bolles, 1975 ). The final part is somewhat speculative in nature: using the preceding observations as a starting point, it argues that a nontrivial similarity exists between recent theories in classical conditioning studies and those in a literature that at first glance appears to bear little relation to it, that is, attribution theories in social psychology.

Classical conditioning: learning associations between two events

Every existing organism must in some way or another be sensitive to both meaningful as well as more coincidental relations between events in the environment, especially when such relations concern biologically significant events. At the same time, it would be maladaptive for an organism if the mere coincident occurrence of two events would be a sufficient condition for the organism to establish a connection between the two. Nevertheless, a coincident occurrence has often been considered a sufficient condition for learning a relation. When doubts were expressed about this idea, they concerned the nature of either one of both events (does one of the events need to have reinforcement value) rather than the nature of the relation itself (i.e., co-occurrence). What follows will demonstrate that every organism can process a wider range of informational relations than the mere joint occurrence of events. In describing this broad range, we aim to list general facts rather than to go deep into possible explanations.

The role of contingency

Instead of using terms indicating co-occurrence, relations can also be expressed in terms of correlation or contingency. What is emphasised in this case is not the temporal relation between two events but their logical relation. Applied to the situation of Pavlov’s dog, this means that a perfect positive correlation is introduced between the CS and the US in the experimental context. In other words, the conditional probability that the US is presented, given that the CS has been presented, equals 1; the probability that the US is presented in the absence of the CS equals 0. This is symbolically expressed as ρ(US/CS) = 1.0 and ρ(US/°CS) = 0. This can probably be further illustrated using what Seligman, Maier and Solomon called “The Pavlovian contingency space” (cf. Figure ​ Figure1 1 ).

Pavlovian contingency space . The x-axis represents the conditional probability that the unconditioned stimulus (US) occurs together with the conditioned stimulus (CS). The y-axis represents the probability that the US occurs without the CS. There is no contingency between both stimuli on the diagonal line where both probabilities are equal (after Seligman, Maier and Solomon, 1971 ).

Given that the essence of the classical conditioning procedure lies in the experimenter’s full control over the two stimuli that are presented, this paradigm lends itself superbly to a study of the effects of variations in the correlational strength of CS-US relations.

Rescorla ( 1968 ) was one of the first to study this issue systematically. Over several experiments ( Rescorla, 1975 ), he demonstrated that animals are sensitive to variations in contingency, ranging from a perfect positive correlation to a perfect negative correlation (respectively below and above the diagonal in Figure ​ Figure1.) 1 .) In this way, he succeeded in translating Pavlov’s two most important findings – excitatory and inhibitory conditioning – into contingency terms. Excitatory conditioning occurs whenever the animal learns that the CS and US tend to go together, in other words when ρ(US/CS) > ρ(US/°CS). A large number of behavioural indices then allow one to determine that the animal is behaving as if it “expects” the US when the CS is presented. Inhibitory conditioning occurs when the animal learns that the US and the CS tend not to go together, ρ(US/CS) < ρ(US/°CS). In this case, when the CS is presented, the animal will behave in a manner that is opposite to how it would behave in excitatory conditioning. When the CS and US are “randomly” presented, with no relation between both stimuli in other words, or ρ(US/CS) = ρ(US/°CS), it is observed that the CS does not acquire a new significance for the animal; in other words, the CS does not elicit a differential reaction. This nonetheless represents a form of active learning: learning that there is no relation is not synonymous to not learning ( Mackintosh, 1973 ; Seligman, 1969 ). Let us illustrate this rather abstract formulation for what is known as “fear conditioning”, which is usually operationalised through the administration of an electrical shock as a US and an external stimulus (e.g., a visual signal) as a CS.

When, within the context of the experiment, the probability of a shock increases after the presentation of a given visual signal, this stimulus acquires a signalling function for the shock: the animal will behave “anxiously” when the CS is presented. If, however, the chance that a shock is administered is lower after the visual stimulus than in the absence of that stimulus, the animal will behave in a fairly “relaxed” fashion when the CS is administered. When the visual signal and the shock are “randomly” presented, the visual signal does not acquire a special meaning. Instead, the context as a whole becomes “fear-inducing” to the animal ( Seligman, 1968 ).

The need for a contingent relation already indicates that mere co-occurrence is not a sufficient condition for an organism to learn the relation between two events. Some way or another, the organism is sensitive to the predictive value of stimuli and the covariance of events in its environment. What follows will illustrate that even a perfect contingency does not constitute a sufficient condition.

Latent inhibition

Lubov (1973) coined the term “latent inhibition” to describe the following observation: when a stimulus is repeatedly presented by itself (i.e., without a US) in a particular context and when it is subsequently always followed by a US, it is difficult to obtain conditioning. It is not all too clear whether one should invoke non-associative or associative principles to explain this phenomenon. On the one hand, it could be argued that the organism no longer is attentive to the stimulus and, as it were, no longer even notices the stimulus because it has repeatedly been presented in the past. On the other hand, it could be argued that the organism has learned that the stimulus is irrelevant because the stimulus has repeatedly been presented on its own and that it afterwards struggles to realise that it is precisely this stimulus that should be considered the signal for an important event ( Mackintosh, 1975 ). There is a certain similarity between latent inhibition and what occurs when a US is administered repeatedly before it is preceded by a CS. Here too, the results show that it is difficult to make this CS acquire the function of a signal for the US. For instance, when a series of shocks are administered in a non-contingent fashion and every shock is afterwards preceded by a tone in that same context, it takes a long time for the organism to learn this tone-shock relation. Again, the explanation for such data can be sought in non-associative or associative principles ( Randich & Lolordo, 1979 ).

Overshadowing

When two stimuli are presented together and consistently followed by a US, often only one of those stimuli will acquire the function of a signal for the US. Pavlov ( 1927 ) already discussed this phenomenon extensively and related it to the difference in “saliency” of the stimuli (as determined by the modality and intensity of the stimuli). Formal classical conditioning models have built in this “saliency” as a parameter – either as a fixed value ( Rescorla & Wagner, 1972 ) or as a fluctuating value in accordance with the relation to the US ( Mackintosh, 1975 ).

Relative information value

Suppose that stimulus A and B are presented together and followed by an electric shock. In group I, stimulus B is also presented separately but not followed by a shock in between the A+B presentations. In group II, B is also presented separately every now and then, but here it is followed by a shock. In group III, only A+B trials are presented. The question is what happens to the signal value of stimulus A. A and a shock are after all paired an equal number of times in all groups. The relative information value of A, however, varies between groups because B is presented separately in groups I and II. In group I, A becomes the best predictor for a shock. B is a better predictor in group II, while the information value of both stimuli is equal in group III. When A is now separately tested in the three groups, conditioned responding varies in accordance with the manipulated information value ( Wagner, 1969 ).

No phenomenon has probably made a larger contribution to clarifying the complexity of conditioning than blocking. It would be impossible to comprehensively list the relevant literature. We will therefore limit ourselves to a description of the basic phenomenon. Kamin ( 1969 ) was the first to bring this phenomenon to light in his “overshadowing” studies. Stimulus A (e.g., a visual signal) is frequently followed by an electric shock. When the conditioning is complete, stimulus B (e.g., an auditory signal) is presented together with stimulus A, and both are followed by a shock. B does not acquire a signal value even though there is a perfect correlation between B and a shock from this moment onward. This is evident from the fact that when B is presented on its own, it does not elicit a response. It is as if the previous conditioning of A is blocking the conditioning of B, hence the term. There are indications that the animal does notice stimulus B, but that it learns as it were that B presents irrelevant or at least redundant information about the US ( Mackintosh, 1978 ).

The above information clearly indicates that mere stimulus co-occurrence is not a sufficient condition for an organism to relate two events. The discussion below will demonstrate that it is also not a necessary condition, which again offers a different perspective on classical conditioning. Instead of an automatic process that plays out in a passive organism, the organism emerges as an active information-processing system.

It is probably possible to relate all the phenomena that were discussed above to the role of contingency. But the question remains what mechanism can be invoked for explaining the role of contingency. Some do not hesitate to postulate that the animal has a cognitive representation of the contingency space ( Alloy & Seligman, 1979 ). Others have drawn more cautious conclusions. As Rescorla notes:

“Most of us are not comfortable with the notion that organisms take in large blocks of time, count up numbers of US events, and somehow arrive at probability estimates … It is tempting to think of simple “tricks” that the organism could use to perform in this apparently rational fashion” ( Rescorla, 1969, p. 84–85 ) .

In other words, being influenced by a correlational relation does not ipso facto imply that the organism concerned has any understanding of this correlation. It is therefore remarkable that Rescorla, who perhaps highlighted the role of contingency more than anyone else, succeeded in developing a theory in which the learning of relations can be traced back to the co-occurrence of two events after all ( Rescorla & Wagner, 1972 ). At the level of formalisation, this theory remains purely descriptive. We would like to note, however, the psychological intuition on which it was built ( Rescorla, 1969 ). The notion of “expectation discrepancy” is central here. As soon as something (important) happens unexpectedly – in other words, it was not predicted – it is as if the animal starts searching for a predictor for this event. Expectation discrepancy appears to be a necessary condition for a stimulus to be interpreted as the signal for this unexpected event. No new learning occurs when either the context (see latent inhibition) or other signals (see blocking) had already predicted the event. This “expectation discrepancy” also explains inhibitory conditioning: when an event that an organism expects to occur in a particular context does not occur, a stimulus that is correlated with this expectation discrepancy may acquire an inhibitory function. Note that this theory emphasizes the role of the environment and the organism’s prior history. We deliberately use metaphors like “to start searching for a predictor”, “to interpret an event” etc. It is as if the facts can only be described in such terms. Such language becomes even more imperative when describing taste aversion.

Taste aversion: The Garcia effect

A short article by Garcia and Koelling published in Psychonomic Science in 1966 was the starting point of the literature on what is now known as the Garcia effect. At the time, there was nothing to suggest that the article would become a classic. Quite the contrary, the article had been rejected by a more renowned journal, which the then editor would later express his regrets about. As is often the case with “classics”, the article was indeed rather weak at the methodological level, but it contained fairly far-reaching theoretical implications. Today, these are referred to as the “Garcia effect”, “the message of Garcia” and “the paradigmatic revolution”. At least 600 articles that were more or less inspired by the Garcia effect have been published since then. This exceptional level of attention does not guarantee scientific relevance in itself. Garcia’s findings may have originally been called into question due to their methodological shortcomings, but the extensive attention has at the least ensured sufficient subsequent independent replications of Garcia’s experiments. The phenomenon is real. The debate about its reach and interpretation, however, remains active today. We first discuss the meaning of “the message of Garcia” by describing a couple of typical experiments. We subsequently reflect on the varying attempts that have been made to interpret this phenomenon.

“The message of Garcia”

What the message of Garcia essentially revolves around is probably best illustrated with an anecdote recounted by Seligman ( Seligman & Hager, 1972 ). After he was served “filet mignon with béarnaise sauce” during a dinner, he became unwell at night. This nausea later proved to be a harbinger of a flu attack. But Seligman had already ascribed it to the béarnaise sauce, and since then he cannot suffer the look, let alone the taste of this sauce. This anecdote raises several questions. Why did he “ascribe” his becoming sick to the béarnaise sauce? Why not to the filet, the dessert or the drinks? Why not to the restaurant or the other guests? Why did his aversion to béarnaise sauce not disappear when it later turned out that the flu was a far more likely cause? Why did béarnaise sauce taste so bad since then? It turns out that answering these questions becomes difficult when this event is translated into a conditioning paradigm, with flavour as the CS and becoming sick as the US (or UR). The most noticeable departures from the normal rules are the extended time period between the CS and US and the difficulty of the extinction, even after the adjusted interpretation. The nature of the US moreover appeared to determine the selection of the CS and, finally, a process that is qualitatively different appears to be at stake here: the béarnaise sauce is avoided not because it is seen as a predictor of nausea, but because it acquires an intrinsically bad flavour.

Garcia’s studies evoke similar questions. The discussion of a typical study will illustrate this further. Garcia and Koelling ( 1966 ) deprived caged rats of water for the duration of the experiment. Every day, the rats were placed in individual test cages that contained a drink tube. After an adjustment period in which clean water was offered, the learning phase began. The water was replaced by a saline solution. Every time the drink tube opening was touched, a visual and auditory stimulus were presented so that every drinking attempt was paired with a “bright-noisy-tasty” constellation of stimuli. In the first group, drinking coincided with a period of radiation (X-rays). 1 In the second group, lithium chloride was used as the saline solution; this has a poisonous effect but the rats cannot distinguish it from a non-poisonous saline solution ( Nachman, 1963 ). In a third group, an electric shock was administered two seconds after drinking. This learning phase was spread over several days in all the groups. On non-conditioning days, the test cage contained only normal water, the drinking of which was not paired with the abovementioned constellation of stimuli. This was followed by a test phase in which either the audiovisual stimulus or the flavour (saline solution) without the audiovisual stimulus was presented during the drinking of clean water. In the X-ray and lithium groups, there was a clear suppression of drinking with the flavour test but not with the audiovisual test, while precisely the opposite occurred in the shock group. In other words, there appears to be an interaction between the nature of the discriminative stimulus and the drinking consequences.

At first glance, several findings regarding conditioned taste aversion indeed contradicted the basic rules of conditioning. First and foremost, there was a clear parametric difference with more typical conditioning preparations: the time interval between the taste CS and administration of the aversive US (induced sickness) was typically much larger. “Records” of 24 hours of difference were set ( Etscorn & Stephens, 1973 )! In the experiment described above, an interaction moreover exists between the nature of the CS and the nature of the US, which is probably the finding that has prompted the most discussion: It is not possible to learn an association between whichever two things. Finally, we already noted that we are seemingly dealing with a qualitatively different phenomenon.

Theoretical reflections

The different attempts to explain flavour aversion can be separated into two main orientations. A first orientation refers to the biological nature of every organism. Through the course of natural selection, every organism has come to be equipped with specific learning mechanisms that, depending on the organism’s adaptation, show specific characteristics as a function of the different challenges the animal faces in its environment. For instance, it is indeed vitally important for an animal to learn the association between certain food attributes and certain metabolic effects. A second orientation attempts to reconcile the properties of flavour aversion with the more general fundamental rules that govern the learning of relations between two events. It does not deny that parametric and perhaps qualitative differences clearly exist between learned taste aversion and the more conventional conditioning findings. But these differences supposedly originate from the particular characteristics of the used stimuli. Insofar that these characteristics can be described, their influence can be assessed through experiments – independent of the flavour aversion phenomenon.

It is indeed remarkable that all the factors that influence learning of an association between two events (cf. below) also have an influence on learned flavour aversion. First, there is the impact of contingency. Inducing a flavour aversion requires a positive correlation: “random” administration of a flavour and US does not have an effect, and a negative correlation between a flavour and the US results in a preference for this flavour ( Best, 1975 ). Latent inhibition is also possible: flavour aversion is slow to develop when the animal is made to taste a certain flavour repeatedly before it is paired with an aversive substance ( Domjan, 1972 ; Elkins, 1973 ). It is equally clear that when the animal is first repeatedly made ill in a way that is non-contingent to ingestion of a particular food, the animal subsequently no longer ascribes this becoming sick to the flavour of the food ( Braveman, 1977 ). “Blocking” finally has also been demonstrated; a learned aversion to a particular flavour can “block” learning of aversion to a different flavour ( Revusky, 1971 ). It is important to note a study by Rudy, Iwens and Best ( 1977 ) in this regard. They first induced a contingency between an external stimulus (black cage) and nausea. When the flavour of saccharine was subsequently involved in this contingency, the animal no longer ascribed the nausea to the flavour. This study is important in two regards. First, it demonstrates that associations between external stimuli and “nausea” can indeed be learned as long as an external stimulus is used that is fairly salient and that can compete with a flavour stimulus in terms of “novelty”. In addition, the results of this experiment certainly do not appear to correspond to what one would expect from a “preparedness” view. If learning of a flavour-nausea contingency is truly “prepared”, it does not seem very plausible that learning of this contingency can be fairly easily “blocked” by a pre-induced artificial or at least unprepared contingency.

These findings indicate that the Garcia effect is not as extraordinary as it appears to be at first glance and that it can in fact be integrated into the more general findings about association learning ( Logue, 1979 ). The particular characteristics of the Garcia effect, however, have urged reflection on the more conventional procedures from a different perspective.

Consider, for instance, the parametric difference between flavour aversion and set-ups that are more conventional in terms of the time lapse between the CS and US (or between the discriminative stimulus and reinforcement). The hypothesis of an after-flavour during nausea was of course the most simple one, but it was emphatically rejected empirically ( Revusky & Garcia, 1970 ). It is therefore almost certain that the Garcia effect is due to a memory phenomenon. When the rat becomes sick, he “remembers” the type of food that may have caused this. Revusky ( 1971 , 1977 ) integrates these findings into what he describes as a more general associative interference theory. This theory inspired Lett ( 1973 , 1974 , 1975 , 1977 ) to demonstrate that a rat is capable of bridging a fairly large time interval between a discriminative stimulus and reinforcement – and this with more conventional procedures. For this to happen, however, the situation must be designed so that the animal is urged to again “call to mind” the discriminative stimulus during reinforcement. It is remarkable that the Garcia effect, which is so deeply rooted in the biological singularity of the organism, is an illustration of the animal’s cognitive capabilities and that it has helped integrate recent findings in the psychology of memory into conditioning studies ( Best & Gemberling, 1977 ; Wagner, 1978 ).

In addition, there is the interaction between the nature of the CS and the US. This interaction is in fact only exceptional when one merely considers the external characteristics of a relationship between two events (contiguity, contingency). It becomes more comprehensible when one assumes that other factors also exist that influence the learning of relations, such as similarity, spatial factors, etc. This insight was probably best articulated by Testa ( 1975 , 1976); he related learned flavour aversion to the more general question of how the animal perceives causal relations in its natural environment. He argues for factors to be integrated into the study of conditioning that had already been previously underlined by gestalt psychologists in relation to perception. We find a similar plea in Revusky ( 1977 ) and Rescorla and Cunningham ( 1979 ).

Conditioning and attribution

After demonstrating how an organism can process complex relations, we have presented a discussion of learned flavour aversion because the latter highlights a central problem: what pushes the animal to selectively attribute certain effects to the ingestion of food or drink when both events are so far removed in time? Rather than viewing this simply as an innate mechanism, it was argued that this phenomenon should be integrated as much as possible into what we know about the learning of associations between events. What then is the meaning of all of this? It seems that there is a fundamental similarity between these findings in the conditioning literature and attribution theory as it was developed in the social psychological literature. This observation suggests that common principles exist that cause both humans and animals to discover causal relations in their environment. Such a speculative observation probably requires a number of prior explanations. Attribution theory is the study of the manner in which certain events are explained in terms of their potential causes. Born from the field of social psychology – a historic coincidence in Kelley’s view ( 1967 ) – the main topic of attribution research was people’s causal analysis of the behaviour of others and one’s self. In other words, on the basis of which rules do I infer the “why” behind my own or other people’s actions? But in essence, a much broader question is at stake in attribution theory: how does one make causal inferences between all sorts of events? The question even arises whether a clear distinction ought to be made between a causal interpretation of events and a causal interpretation of actions. The distinction between “cause” and “reason” is key here, and it was also the focus of a recent discussion ( Buss, 1978 ; Harvey & Tucker, 1979 ; Kruglanski, 1979 ; Buss, 1979 ). Only causal interpretations of events will be discussed below. To put it in more trivial terms, when a rat is administered a shock by the experimenter, it might ask itself: What is this shock due to (asks after the cause)? It does not ask: why did this experimenter give me a shock (asks after the reason)? Both are “why” questions, but they are logically different from each other. Second, a distinction should be made between the attribution process and the content of the attributions ( Nisbett & Wilson, 1977 ; Kruglanski, 1979 ). At the level of contents, it is obvious that any animal-human comparison would be a tenuous one. But this is also true for a comparison between mutual humans, if only because of cultural differences ( Kruglanski, 1979 ). As regards attribution as process, it is probably possible to arrive at more general statements about the heuristics that apply to both humans and animals. A third introductory remark concerns the status of the concept of attribution. Attribution is intended as a “mediating” concept that can either be assigned a reality value or an “as if” nature. This is true for most “cognitive” concepts that were designed to mediate between input and output (consider, for instance, the concept of “expectancy”). In our view, there is a trend towards increasing emphasis on the “as if” nature of attributions in social psychology. The most common descriptions – somewhat schematically – present this sequence as follows: 1. something occurs (S) – 2. the organism asks itself “why” – 3. following deliberation, it arrives or does not arrive at a judgement – 4. it acts in a manner that is consistent with this (R). If assigned a reality value, it is possible to render the typically non-observable links 2. and 3. observable in humans by simply inquiring after them. It would not be exaggerated to state that this is the focus of most attribution research. And any study of attributions in animals is of course impossible in this respect. But it has been asked more and more whether the “links” do not acquire a different status precisely because they are made observable. Let us again briefly go back to Seligman’s anecdote about the béarnaise sauce. If Seligman is asked: “Why did you become sick?”, he will answer: “Because I had a flu attack.” In other words, does a “conscious” reflection on the occurrence of an event not respond to different rules than the total original experience of this occurrence? Is this not where the truth lies of Pascal’s statement that “le cœur a ces raisons que la raison ne connaît pas”? In a rather extensive article, Nisbett and Wilson ( 1977 ) defended the proposition that these cognitive mediating processes circumvent every form of introspection. To support their argument, they cited a number of statements by cognitive psychologists, including Neisser and Mandler, that we would like to cite here. For instance, Neisser writes that “the constructive processes (of encoding perceptual sensations) themselves never appear in consciousness, their products do” (Neisser, 1967, p. 301). And Mandler considers that “there are many systems that cannot be brought into consciousness, and probably most systems that analyze the environment in the first place have that characteristic. In most of these cases, only the products of cognitive and mental activities are available to consciousness” ( Mandler, 1975, p. 245 ). Although Nisbett and Wilson’s proposition is debatable ( Smith & Miller, 1978 ), Langer ( 1978 ) does not hesitate to go one step further: she simply denies the mediating role of conscious cognitions in most of our day-to-day actions: “Much psychological research relies on a theoretical model that depicts the individual as one who is cognitively aware most of the time, and who consciously, constantly, and systematically applies “rules” to incoming information about the environment in order to formulate interpretations and courses of actions. Attribution theorists rely on this model in attempting to uncover the sources of regularities in human behaviour. But if in fact it can be demonstrated that much complex human behaviour can and does occur without these assumed cognitive assessments, then we must question both pervasiveness of attribution making as a cognitive process and the assumptions made by most social psychologists” ( Langer, 1978, p. 35 ). We find a similar plea to look for very simple heuristics to explain the notion of attribution in Kahneman and Tversky ( 1973 ), Pryor and Kriss ( 1977 ) and especially Taylor and Fiske ( 1978 ) who concluded that most attribution processes “seem to occur automatically and substantially without awareness, and as such, they differ qualitatively from the intentional, conscious, controlled kind of search which we like to think characterises all our behaviour” ( Taylor & Fiske, 1978, p. 283 ).

These introductory explanations probably create more room for the proposition that there is something common about the way that humans and animals infer causal relations. We rely on a recent overview article by Kelley and Michela ( 1980 ) on attribution theory to buttress this claim in a more direct way. They first offer the general scheme that is implicitly contained in the study field of attribution (Figure ​ (Figure2 2 ).

Schematic model of attribution research (after Kelley & Michela, 1980 ).

As indicated above, any type of direct research into (2) is evidently impossible with animals. One has to limit oneself to manipulations of (1) and inferring what happens in (2) from a change in (3). But as also noted above, this limitation probably also applies to studies of attribution in humans. On the antecedent side (1) then, there is a clear similarity between the factors influencing the nature of attributions and conditioning. Let us illustrate this using the principles that Kelley and Michela distilled from attribution literature. These principles hold that certain aspects of the information that the organism is confronted with lead to attributions. Almost every one of these is a principle that we already mentioned in our discussion of the factors that influence conditioning.

• Covariance : The ANOVA model. This principle was primarily emphasised by Kelley himself ( Kelley, 1967 , 1973 ). “The effect is attributed to that condition which is present when the effect is present and which is absent when the effect is absent” ( Kelley, 1967, p. 194 ). This covariance principle is of course heavily analogous, if not identical, to the role of contingency in classical conditioning. This raises a twofold observation: first, there is no reason to suppose, as Kelley does, that the influence of this covariance principle must revert to a model of the human as a “naïve” scientist who thinks according to an ANOVA model (he probably only does so in the context of attribution experiments!). As noted above, the influence of contingency does not necessarily imply that the organism has any notion of contingency. In addition, there is the dilemma of moving from a correlation judgement to a causal judgement. A causal relation after all implies a correlation, but the reverse does not hold. Is a causal judgement only possible when one implicitly also has knowledge of the mechanisms that connect cause and effect? Or are other conditions necessary in addition to perfect correlation for two events to be perceived in a cause-effect relation? This dilemma brings us to the question posed by Michotte ( 1954 ): Is causality a phenomenal experience or a “post hoc” reflection? It is interesting to note in this regard that Testa ( 1974 ) relied on Michotte’s findings to explain flavour aversion.
• Saliency : “The notion here is that an effect is attributed to the cause that is most salient in the perceptual field at the time the effect is observed.” ( Kelley & Michela, 1980, p. 466 ). This “saliency” is again a factor that plays a role in conditioning (see below).
• Similarity and Contiguity : The principle of contiguity does not require much explanation to be related to conditioning. Rescorla and Furrow ( 1977 ) convincingly demonstrated the role of “similarity”, which has always been seen as an associative principle, within a conditioning paradigm.
• Primacy : “The general notion here is that a person scans and interprets a sequence of information until he attains an attribution from it and then disregard later information or assimilates it to his earlier impression” ( Kelley & Michela, 1980, p. 467 ). Conditioning literature analogies also exist for this. It for instance takes a long time for the animal to recognise a “random” relationship such as when a tone and a shock are “randomly” presented but this random series begun with a contingency between both events. The reverse is also true: a contingency is also learned with difficulty in the case of a random start and subsequent contingency ( Alloy & Seligman, 1979 ).

Conditioning literature parallels also exist for the interaction between the nature of the information on the one hand and the existing “beliefs” or causal models and the motivational component (Figure ​ (Figure2) 2 ) on the other. The “blocking” phenomenon can be considered a causal model that interferes with the learning of other causal relations: both humans and animals do not look for every possible cause but instead suffice themselves with one sufficient cause. In addition, the motivational component has always been central to conditioning. To explain this using anthropomorphic terms, the animal only asks itself a why-question when something important occurs.

We here touch on a point that made us relate the notion of attribution to findings on conditioning. We prefer the term attribution over the term association to denote what happens during conditioning. Not only because “association” is a historically heavily charged concept, but because the term does not permit a distinction between the propositions “event X reminds me of event Y” and “I ascribe event X to event Y”. To again illustrate this using Seligman’s example: when he becomes nauseous, he can perfectly remember the full dinner event, but only one relation, one “attribution” is made with the béarnaise sauce. Remembrance is a necessary but not a sufficient condition to establish a causal relation between two events. Winograd ( 1971 ) described this as follows: “Let us imagine that I emerge from my house in the morning and find a flat tire on my car. It occurs to me immediately that around nine o’clock the previous evening, while driving home, I heard a disturbingly loud noise as I drove over something in the road. Now, 12 hours later, I “associate” the flat tire with the impact. This is not an association in the usual S-R contiguity sense; rather, I have related two events which were separated by a long period of time. I can do this only if I have a record of the earlier event, or memory. In fact, I have many memories of previous events, and that is the problem. The question to be dealt with is one of trace selection or contact, of how I have related these two particular events” ( Winograd, 1971, p. 272–273 ). This, precisely, is the dilemma posed by the Garcia effect, looked at from a different perspective. It is why use of the term “attribution” rather than the term “association” becomes even more imperative when we keep the phenomenon of flavour aversion in mind. As Revusky and Garcia write, “Probably, the rat can really associate these events, but will not attribute the production of shock to the flavored water. In other words, a rat can learn that consumption of flavored water precedes shock, but will not readily learn that consumption of flavoured water produces shock” ( Revusky & Garcia, 1970, p. 41 ). A bit further, both authors write: “This paper would probably be more precise if, whenever the term “association” is used, “attribution” were to be substituted” (p. 43). Does, after this discussion, it still seems absurd that an animal responds “as if” it were making an attribution?

Of course, a change in terminology is only a pseudo-solution to a dilemma that has been key since Pavlov’s dog: How is a relation between two events learned? This contribution offers only limited insight into this question, and it is quite fortunate that the effective learning of such relations does not depend on its explanation. But the search for such an explanation becomes imperative the moment it is established that the learning of relations fails. Because this probably constitutes a true breeding ground for human and animal suffering: the inability to explain an important event.

Finally, this contribution might foster the impression that contemporary conditioning psychology tries to anthropomorphise the rat too much, when in the past humans were seen too much as rats. But a rat is a rat and a human a human. Nevertheless, it does not seem very fruitful to me to hermetically seal off both study domains. Whereas Estes notes that “the thought arises that the processes and mechanisms of human cognition represent specializations and elaborations of processes and mechanisms which can advantageously be studied in animals that learn as well as in machines that think” ( Estes, 1975, p. 6 ), this contribution was written from the conviction that Estes’ first alternative continues to be valuable. For as long as a computer does not salivate upon seeing a chunk of meat, “Pavlov’s dog” continues to be a fascinating phenomenon.

The use of X-rays in this experiment probably calls for some explanation about the prior history of the Garcia effect. Commissioned by the ministry of defence, Garcia and his collaborators completed a series of investigations into the influence of ionising radiation on animal behaviour during the fifties. Their most important finding was that such radiation – even when administered in small doses – had an aversive nature to the animal, and the behavioural component that this could most clearly be inferred from was the strongly reduced drink and food intake. It proved much more difficult, however, to use these radiation effects to teach spatial avoidance behaviour ( Garcia, Kimeldorf & Hunt, 1961 ).

Competing Interests

The author has no competing interests to declare.

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What did Ivan Pavlov study?

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Ivan Pavlov

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Ivan Pavlov gave up studying theology to enter the University of St. Petersburg , where he studied chemistry and physiology . After receiving an M.D. at the Imperial Medical Academy in St. Petersburg , he studied in Germany under the direction of the cardiovascular physiologist Carl Ludwig and the gastrointestinal physiologist Rudolf Heidenhain.

Ivan Pavlov developed an experiment testing the concept of the conditioned reflex . He trained a hungry dog to salivate at the sound of a metronome or buzzer, which was previously associated with the sight of food . He later developed an approach that emphasized the importance of conditioning in studies relating human behaviour to the nervous system .

In addition to his conditioning work, Ivan Pavlov devised an operation to prepare a miniature stomach , which was isolated from ingested foods but retained its vagal nerve supply. The procedure allowed him to study the gastrointestinal secretions in animals . For his efforts he received the Nobel Prize for Physiology or Medicine in 1904.

Having worked with Carl Ludwig , Ivan Pavlov’s first independent research was on the physiology of the circulatory system . From 1888 to 1890, in St. Petersburg, he investigated cardiac physiology and blood pressure regulation. He became so skillful as a surgeon that he could introduce a catheter into a dog’s femoral artery almost painlessly.

Ivan Pavlov (born September 14 [September 26, New Style], 1849, Ryazan, Russia—died February 27, 1936, Leningrad [now St. Petersburg]) was a Russian physiologist known chiefly for his development of the concept of the conditioned reflex . In a now-classic experiment, he trained a hungry dog to salivate at the sound of a metronome or buzzer, which was previously associated with the sight of food. He developed a similar conceptual approach, emphasizing the importance of conditioning , in his pioneering studies relating human behaviour to the nervous system . He was awarded the Nobel Prize for Physiology or Medicine in 1904 for his work on digestive secretions.

Pavlov, the first son of a priest and the grandson of a sexton, spent his youth in Ryazan in central Russia . There, he attended a church school and theological seminary, where his seminary teachers impressed him by their devotion to imparting knowledge. In 1870 he abandoned his theological studies to enter the University of St. Petersburg , where he studied chemistry and physiology. After receiving the M.D. at the Imperial Medical Academy in St. Petersburg (graduating in 1879 and completing his dissertation in 1883), he studied during 1884–86 in Germany under the direction of the cardiovascular physiologist Carl Ludwig (in Leipzig) and the gastrointestinal physiologist Rudolf Heidenhain (in Breslau).

Having worked with Ludwig, Pavlov’s first independent research was on the physiology of the circulatory system . From 1888 to 1890, in the laboratory of Botkin in St. Petersburg, he investigated cardiac physiology and the regulation of blood pressure .

He became so skillful a surgeon that he was able to introduce a catheter into the femoral artery of a dog almost painlessly without anesthesia and to record the influence on blood pressure of various pharmacological and emotional stimuli. By careful dissection of the fine cardiac nerves , he was able to demonstrate the control of the strength of the heartbeat by nerves leaving the cardiac plexus; by stimulating the severed ends of the cervical nerves, he showed the effects of the right and left vagal nerves on the heart.

Pavlov married a pedagogical student in 1881, a friend of the author Fyodor Dostoyevsky , but he was so impoverished that at first they had to live separately. He attributed much of his eventual success to his wife, a domestic, religious, and literary woman, who devoted her life to his comfort and work. In 1890 he became professor of physiology in the Imperial Medical Academy, where he remained until his resignation in 1924. At the newly founded Institute of Experimental Medicine, he initiated precise surgical procedures for animals, with strict attention to their postoperative care and facilities for the maintenance of their health .

During the years 1890–1900 especially, and to a lesser extent until about 1930, Pavlov studied the secretory activity of digestion . While working with Heidenhain, he had devised an operation to prepare a miniature stomach , or pouch; he isolated the stomach from ingested foods, while preserving its vagal nerve supply. The surgical procedure enabled him to study the gastrointestinal secretions in a normal animal over its life span. This work culminated in his book Lectures on the Work of the Digestive Glands in 1897.

By observing irregularities of secretions in normal unanesthetized animals, Pavlov was led to formulate the laws of the conditioned reflex, a subject that occupied his attention from about 1898 until 1930. He used the salivary secretion as a quantitative measure of the psychical, or subjective, activity of the animal, in order to emphasize the advantage of objective, physiological measures of mental phenomena and higher nervous activity. He sought analogies between the conditional (commonly though incorrectly translated as “conditioned”) reflex and the spinal reflex.

According to the English physiologist Sir Charles Sherrington , the spinal reflex is composed of integrated actions of the nervous system involving such complex components as the excitation and inhibition of many nerves , induction (i.e., the increase or decrease of inhibition brought on by previous excitation), and the irradiation of nerve impulses to many nerve centres. To these components, Pavlov added cortical and subcortical influences, the mosaic action of the brain , the effect of sleep on the spread of inhibition, and the origin of neurotic disturbances principally through a collision, or conflict, between cortical excitation and inhibition.

Beginning about 1930, Pavlov tried to apply his laws to the explanation of human psychoses . He assumed that the excessive inhibition characteristic of a psychotic person was a protective mechanism—shutting out the external world—in that it excluded injurious stimuli that had previously caused extreme excitation. In Russia this idea became the basis for treating psychiatric patients in quiet and nonstimulating external surroundings. During this period Pavlov announced the important principle of the language function in human beings as based on long chains of conditioned reflexes involving words. The function of language involves not only words, he held, but an elaboration of generalizations not possible in animals lower than humans.

Ivan Pavlov and the Theory of Classical Conditioning

Classical Conditioning (Pavlov)

Classical conditioning is a reflexive or automatic type of learning in which a stimulus acquires the capacity to evoke a response that was originally evoked by another stimulus.

Contributors Key Concepts Resources and References

Contributors

• Ivan Pavlov (1849 – 1936)
• John B. Watson (1878 – 1958)

Key Concepts

Several types of learning exist. The most basic form is associative learning, i.e., making a new association between events in the environment [1] . There are two forms of associative learning: classical conditioning (made famous by Ivan Pavlov’s experiments with dogs) and operant conditioning.

Pavlov’s Dogs

In the early twentieth century, Russian physiologist Ivan Pavlov did Nobel prize-winning work on digestion [2] . While studying the role of saliva in dogs’ digestive processes, he stumbled upon a phenomenon he labeled “psychic reflexes.” While an accidental discovery, he had the foresight to see the importance of it. Pavlov’s dogs, restrained in an experimental chamber, were presented with meat powder and they had their saliva collected via a surgically implanted tube in their saliva glands. Over time, he noticed that his dogs who begin salivation before the meat powder was even presented, whether it was by the presence of the handler or merely by a clicking noise produced by the device that distributed the meat powder.

Fascinated by this finding, Pavlov paired the meat powder with various stimuli such as the ringing of a bell. After the meat powder and bell (auditory stimulus) were presented together several times, the bell was used alone. Pavlov’s dogs, as predicted, responded by salivating to the sound of the bell (without the food). The bell began as a neutral stimulus (i.e. the bell itself did not produce the dogs’ salivation). However, by pairing the bell with the stimulus that did produce the salivation response, the bell was able to acquire the ability to trigger the salivation response. Pavlov therefore demonstrated how stimulus-response bonds (which some consider as the basic building blocks of learning) are formed. He dedicated much of the rest of his career further exploring this finding.

In technical terms, the meat powder is considered an unconditioned stimulus (UCS) and the dog’s salivation is the unconditioned response (UCR). The bell is a neutral stimulus until the dog learns to associate the bell with food. Then the bell becomes a conditioned stimulus (CS) which produces the conditioned response (CR) of salivation after repeated pairings between the bell and food.

John B. Watson: Early Classical Conditioning with Humans

John B. Watson further extended Pavlov’s work and applied it to human beings [3] . In 1921, Watson studied Albert, an 11 month old infant child. The goal of the study was to condition Albert to become afraid of a white rat by pairing the white rat with a very loud, jarring noise (UCS). At first, Albert showed no sign of fear when he was presented with rats, but once the rat was repeatedly paired with the loud noise (UCS), Albert developed a fear of rats. It could be said that the loud noise (UCS) induced fear (UCR). The implications of Watson’s experiment suggested that classical conditioning could cause some phobias in humans.

Additional Resources and References

• McSweeney and Murphy: The Wiley Blackwell Handbook of Operant and Classical Conditioning. : This brand new book contains an up-to-date, inclusive account of a core field of psychology research, with in-depth coverage of operant and classical conditioning theory, its applications, and current topics including behavioral economics.
• Mackintosh, N. J. (1983). Conditioning and associative learning (p. 316). Oxford: Clarendon Press.
• Pavlov, I. P., & Anrep, G. V. (2003). Conditioned reflexes. Courier Corporation.
• Watson, J. B. (2013). Behaviorism. Read Books Ltd.

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Classical Conditioning

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• Jorge Mallea 3 ,
• Javier Bustamante 4 ,
• Gonzalo Miguez 5 &
• Mario A. Laborda 5  

Introduction

Classical or Pavlovian conditioning is a type of learning where two or more events of the environment are associated. This type of learning helps organisms to organize their behavior and represent their world. In a classic experiment, Pavlov ( 1927 ) discovered that a dog would salivate to the presence of a sound if this sound was previously presented contiguously with food powder. Pavlov called the food powder an unconditioned stimuli (US) that evoked a response by its own, which he called an unconditioned response (UR). The sound was originally a neutral stimulus that did not produce any relevant response, but after being presented with the food, the sound became a conditioned stimulus (CS), which elicited a conditioned response (CR). To Pavlov, this response was “conditional” to the unconditioned stimulus, thereby the name. The study of classical conditioning has changed since Pavlov’s years; we now know that classical conditioning is involved in much more than only...

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Classical Conditioning – The Pavlov’s Dogs Experiment

Have you ever heard a song or tune from your childhood and felt an instant rush of nostalgia or happiness? That tune and the happiness/nostalgic feeling are interconnected by association, which we call Classical Conditioning.

Classical Conditioning is a psychological phenomenon in which one learns by pairing two or more stimuli to create an association. It is the process of creating a link between a conditioned stimulus and a conditioned response.

Who Discovered Classical Conditioning ?

The phenomenon of Classical Conditioning was discovered by Ivan Pavlov. Ivan Pavlov was a Russian Physiologist who was interested in understanding canine physiology and was especially interested in their digestive systems.

He began to observe dogs and their eating patterns to identify when they begin to salivate. Through his observations, he believed that dogs begin to salivate when they heard the bell that was rung before the food was presented.

To prove his theory, Pavlov built a machine that would accurately determine and measure the amount of saliva produced when the food was presented. Thus began the infamous Pavlov’s dogs experiment.

What is the Pavlov’s Dogs Experiment ?

Pavlov initially placed the food in front of the dog and recorded the level of salivation. He did this a couple of times to measure and assess why the dog was salivating.

After the first couple of trials, he began to ring a bell. He would ring the bell and wait approximately 5 seconds before presenting the food. The dogs continued to salivate only when the food was present. However, after repetitive exposure to the bell and the food, the dogs began to salivate upon hearing the bell.

This means that the dog began to associate the bell with food. This leads to salivation when hearing the bell.

Core Concept Of Classical Conditioning

This experiment led to the discovery of a type of learning called Classical Conditioning (as termed by Pavlov). The experiment was conducted in 1906 and was a major catalyst in the development and understanding of learning and behaviour theories.

The experiment consists of 4 different elements. These are:

1) Unconditioned Stimulus

This is a certain object or stimulus that triggers an automatic/involuntarily bodily response. This is an unconscious process and has not been previously learnt. In this case, the food is considered to be the unconditioned stimuli.

For example, for a student, the smell of the food from the mess/canteen is considered to be the unconditioned stimuli.

2) Unconditional Response

This is the automatic and involuntary response that occurs when presented with the object or the stimulus. This response is generally unlearnt and usually occurs due to the processes of the Central Nervous System (CNS). In this case, the salivation of the dogs is the Unconditioned Response.

For example, the hunger and salivation of the student are considered to be the unconditioned response.

3) Conditioned Stimulus

This is also known as the Neutral Stimulus. This stimulus is presented repeatedly until the association between the object and the response is formed. If the object is repeatedly presented (in this case the food), it will start to evoke the same response. In this case, the bell is considered to be the conditioned stimulus.

For example, the lunch bell is paired with the smell of the food. Hence the bell is associated with lunchtime. Therefore, the bell becomes the conditioned stimulus.

4) Conditioned Response

This is the response obtained after repeated exposure to the conditioned stimulus (which is the bell). This is the response that occurs once the stimulus and response have been associated. The conditioned response is salivating upon hearing the bell.

For example, the bell is now associated with the food from the mess/canteen. Hence, the student may get hungry/salivate upon hearing the sound of the bell. This indicates that classical conditioning has occurred.

Common Example – Conditioning Theory Of Learning

A great example of this is when you smell your mom’s perfume. You may have grown up used to the smell of your mom’s perfume. The perfume reminds you of your mother and the great times you shared when you were growing up. You are exposed to the perfume several times while growing up; you begin to associate it with happiness.

Several years later, if you catch a sniff of the perfume in a supermarket, you may associate it with happiness without actually consciously thinking of your childhood or your mother. This is due to learning by association otherwise known as Classical Conditioning.

There are three other aspects that we must understand and take into account when learning about classical conditioning. They are:

a) Extinction

This is a phenomenon in which the conditioned stimulus (i.e. the bell) is presented excessively without the unconditioned stimulus (i.e. dog food). This overexposure results in the process of unlearning. Eventually, the bell will no longer result in a conditioned response.

For example, while training children to potty train, the parents might give a reward every time the child uses the toilet. However, over time as the child continues to use the toilet, the parent will stop providing the rewards. Due to the overexposure, the child will eventually continue the behavior without association.

b) Generalization

This occurs when the conditioned stimulus is generalized, and therefore causes a conditioned response. For example, the dog may generalize the sound of other bells and may begin to salivate.

This can be found in the case of Little Albert. He was taught to fear a white rabbit using classical conditioning. However, he began to generalize that phobia to other objects of similar shape, size and colour. He also began to fear other objects such as mice, hamsters etc. This is known as generalization.

c) Discrimination

This is the opposite response to Generalization. This occurs when the person/ animal can discriminate between different stimuli and therefore will not produce the same reaction to the different stimuli.

This can be seen when one has a very certain phobia. For example, a person who has a phobia of cockroaches may not have a phobia of spiders or other insects even though they are similar.

What are the applications of Classical Conditioning in Psychology ?

Classical Conditioning has helped several psychologists understand how people learn and behave. Classical Conditioning helped pave the way for understanding certain pathological conditions (i.e. phobias, drug dependency and aversions) and their treatments. These include:

a) Phobias and Systematic Desensitization

A famous experiment conducted by John B Watson called Little Albert helps us understand how phobias are formed. Watson used the same method of classical conditioning to instil fear in a little boy named Albert. Albert was initially presented with a small rat for the first few trials.

After the first few trials, the rat was presented with a loud noise. Although Albert was initially not afraid of the rat, the association between the rat and the loud noise was formed. This resulted in causing him extreme fear when he saw the rat. This resulted in Albert having a phobia of rats.

Classical Conditioning can also be used to help get ready for phobias. This is usually done using a method of Systematic Desensitization. This treatment works by creating a hierarchy of fear. The client will identify and rank their fears from lowest to highest.

For example, a client who has a fear of lizards may feel fear at 10% while talking about them, 30% fear while looking at a picture, 50% watching a video of a lizard and 70% of fear while one is in the room.

The therapist then begins to work up the hierarchy while pairing deep breathing exercises.

For example, the therapist shows the client an image of a lizard and then guides them through deep breathing. This is repeated several times until the client no longer feels scared to see an image. They then move on to the next stage of the hierarchy.

This is what the hierarchy for herpetophobia (Fear of Lizards) would look like.

Vicarious Conditioning is the occurrence of developing fear and becoming conditioned due to watching someone else.

For example, if you watch your mother running away from a spider, you may also become conditioned into thinking that spiders are something that evokes fear. This may lead to arachnophobia later on.

b) Drug Dependency and Aversion Therapy

Drugs cause a feeling of “ecstasy” or a “high”. This feeling of high results in the user repeatedly using. The feeling of ecstasy and the substance become paired, thus the user will continue to use the substance. They may even become extremely dependent on it, resulting in an abuse disorder.

Aversion Therapy is a treatment method used to combat abuse disorder. This is behavioural therapy method in which there is a pairing between unwanted behaviour and discomfort.

For example, someone who is addicted to alcohol may be required to snap a rubber band on their wrist every time they think of alcohol.

c) Classical Conditioning and Attitude Formation

Classical Conditioning has shown a significant outcome in attitude formation. Classical Conditioning has shown the ability to determine and change a person’s attitude/ feelings towards a particular object.

For example, a child grows up seeing her mother react negatively to Native Americans. Every time her mother comes across someone of Native American descent, she gets angry. She begins to associate anger with the Native Americans. She may begin to view them negatively and may even grow up and treat them the same.

Hence, classical conditioning has affected her attitude towards a certain race. This is attitude formation.

Ivan Pavlov’s experimentation with learning and behaviour caused a ripple effect throughout the psychological community. It promoted the development of several other theories of learning. It also helped us understand human behaviour and helped in the evolution of treatment methods.

So next time you come across Pavlov and Classical Conditioning, I hope this article rings a bell.

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Ivan Pavlov and His Discovery of Classical Conditioning

• Classical Conditioning
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Ivan Pavlov was a Russian physiologist best known in psychology for his discovery of classical conditioning. During his studies on the digestive systems of dogs, Pavlov noted that the animals salivated naturally upon the presentation of food.

However, he also noted that the animals began to salivate whenever they saw the white lab coat of an experimental assistant. It was through this observation that Pavlov discovered that by associating the presentation of food with the lab assistant, a conditioned response occurred. Pavlov was also able to demonstrate classical conditioning in his subjects by associating food with sound of a tone.

Learn more about Ivan Pavlov and his contributions to the field of psychology.

Pavlov discovered classical conditioning in the 1890s and published his results in 1897. The discovery had a reverberating influence on psychology. Pavlov's discovery had a major influence on other thinkers including John B. Watson and contributed significantly to the development of the school of thought known as behaviorism.

Take a closer look at Ivan Pavlov's life and career in this brief biography.

Ivan Pavlov is best known for:

• Classical conditioning
• Research on physiology and digestion
• 1904 Nobel Prize in Physiology

Ivan Petrovich Pavlov was born on September 14, 1849, in the village of Ryazan, Russia, where his father was the village priest. His earliest studies were focused on theology, but reading Charles Darwin's On the Origin of the Species had a powerful influence on his future interests.

He soon abandoned his religious studies and devoted himself to the study of science. In 1870, he began studying the natural sciences at St. Petersburg University.

Pavlov's primary interests were the study of physiology and natural sciences. He was a founder of the Russian Physiological Society and also served as its first president, a position he held for 19 years.  

"Science demands from a man all his life. If you had two lives that would not be enough for you. Be passionate in your work and in your searching, "  Pavlov once suggested.

So, how did his work in physiology lead to his discovery of classical conditioning?

Ivan Pavlov's Discovery of Classical Conditioning

While researching the digestive function of dogs, he noted his subjects would salivate when they saw the person who was delivering food. In a series of well-known experiments , he presented a variety of stimuli before the presentation of food, eventually finding that, after repeated association, a dog would salivate to the presence of a stimulus other than food.

Pavlov termed this response a conditional reflex . Pavlov also discovered that these reflexes originate in the cerebral cortex of the brain.

Pavlov received considerable acclaim for his work, including a 1901 appointment to the Russian Academy of Sciences and the 1904 Nobel Prize in Physiology. The Soviet government also offered substantial support for Pavlov's work, and the Soviet Union soon became a leading center of physiology research.

He died on February 27, 1936.

Ivan Pavlov's Contributions to Psychology

Many outside of psychology may be surprised to learn that Pavlov was not a psychologist at all. Not only was he not a psychologist; he reportedly was skeptical of the emerging field of psychology altogether.

However, his work had a major influence on the field, particularly on the development of behaviorism . His discovery and research on reflexes influenced the growing behaviorist movement, and his work was often cited in John B. Watson's writings.

Other researchers utilized Pavlov's work in the study of conditioning as a form of learning. His research also demonstrated techniques of studying reactions to the environment in an objective scientific method.

One of Pavlov's earliest publications was his 1897 text The Work of the Digestive Glands , which centered on his physiology research.

Later works that focused on his discovery of classical conditioning include his 1927 book Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex and Lectures on Conditioned Reflexes: Twenty-five Years of Objective Study of the High Nervous Activity (Behavior) of Animals which was published one year later.

A Word From Verywell

Ivan Pavlov may not have set out to change the face of psychology, but his work had a profound and lasting influence on the science of the mind and behavior. His discovery of classical conditioning helped establish the school of thought known as behaviorism.

Thanks to the work of behavioral thinkers such as Watson and Skinner, behaviorism rose to be a dominant force within psychology during the first half of the twentieth century. 

Brown RE, Molnár Z, Filaretova L, Ostrovsky M, Piccolino M, Lorusso L. The 100th anniversary of the Russian Pavlov Physiological Society. Physiology (Bethesda) . 2017;32(6):402-407. doi:10.1152/physiol.00023.2017

Eelen P. Classical conditioning: Classical yet modern . Psychol Belg . 2018;58(1):196-211. doi:10.5334/pb.451

McCabe B. Hopkins researcher discovers everything we know about Pavlov is wrong . Johns Hopkins Magazine . 2014.

Nobel. The Nobel Prize in Physiology or Medicine 1904: Ivan Pavlov - Biographical

Santana LH. Comparing Watson's behaviorism and Meyer's objectivism: Reassessing traditional assumptions in psychology . 2023.

Pavlov I. The work of the digestive glands . In: Scientific and Medical Knowledge Production, 1796-1918. Routledge. 2023:157-173

Schultz, D. P., & Schultz, S. E (Eds.). (2012). A History of Modern Psychology . Australia Belmont, CA: Thomson/Wadsworth.

Todes, DP. Ivan Pavlov: A Russian Life in Science . New York: Oxford; 2014.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Biography of Ivan Pavlov, Father of Classical Conditioning

National Library of Medicine / Public Domain

• Archaeology

Ivan Petrovich Pavlov (September 14, 1849 - February 27, 1936) was a Nobel Prize-winning physiologist best known for his classical conditioning experiments with dogs. In his research, he discovered the conditioned reflex, which shaped the field of behaviorism in psychology.

Fast Facts: Ivan Pavlov

• Occupation : Physiologist
• Known For : Research on conditioned reflexes ("Pavlov's Dogs")
• Born : September 14, 1849, in Ryazan, Russia
• Died : February 27, 1936, in Leningrad (now St. Petersburg), Russia
• Parents : Peter Dmitrievich Pavlov and Varvara Ivanovna Uspenskaya
• Education : M.D., Imperial Medical Academy in St. Petersburg, Russia
• Key Accomplishments : Nobel Prize for Physiology (1904)
• Offbeat Fact : A lunar crater on the Moon was named after Pavlov.

Early Years and Education

Pavlov was born on September 14, 1849, in the small village of Ryazan, Russia. His father, Peter Dmitrievich Pavlov, was a priest who hoped that his son would follow in his footsteps and join the church. In Ivan's early years, it seemed that his father's dream would become a reality. Ivan was educated at a church school and a theological seminary. But when he read the works of scientists like Charles Darwin and I. M. Sechenov, Ivan decided to pursue scientific studies instead.

He left the seminary and began studying chemistry and physiology at the University of St. Petersburg. In 1875, he earned an M.D. from the Imperial Medical Academy before going on to study under Rudolf Heidenhain and Carl Ludwig, two renowned physiologists. 

Personal Life and Marriage

Ivan Pavlov married Seraphima Vasilievna Karchevskaya in 1881. Together, they had five children: Wirchik, Vladimir, Victor, Vsevolod, and Vera. In their early years, Pavlov and his wife lived in poverty. During the hard times, they stayed with friends, and at one point, rented a bug-infested attic space.

Pavlov's fortunes changed in 1890 when he took an appointment as the Professor of Pharmacology at the Military Medical Academy. That same year, he became the director of the Department of Physiology at the Institute of Experimental Medicine. With these well-funded academic positions, Pavlov had the opportunity to further pursue the  scientific studies  that interested him.

Research on Digestion

Pavlov's early research focused primarily on the physiology of digestion . He used surgical methods to study various processes of the digestive system. By exposing portions of a dog's intestinal canal during surgery, he was able to gain an understanding of gastric secretions and the role of the body and mind in the digestive process. Pavlov sometimes operated on live animals, which was an acceptable practice back then but would not occur today due to modern ethical standards.

In 1897, Pavlov published his findings in a book called “Lectures on the Work of the Digestive Glands.” His work on the physiology of digestion was also recognized with a Nobel Prize for Physiology in 1904. Some of Pavlov's other honors include an honorary doctorate from Cambridge University, which was awarded in 1912, and the Order of the Legion of Honor, which was given to him in 1915.

Discovery of Conditioned Reflexes

Although Pavlov has many notable accomplishments, he is most well known for defining the concept of conditioned reflexes. 

A conditioned reflex is considered a form of learning that can occur through exposure to stimuli. Pavlov studied this phenomenon in the lab through a series of experiments with dogs. Initially, Pavlov was studying the connection between salivation and feeding. He proved that dogs have an unconditioned response when they are fed — in other words, they are hard-wired to salivate at the prospect of eating.

However, when Pavlov noticed that the mere sight of a person in a lab coat was enough to cause the dogs to salivate, he realized that he had accidentally made an additional scientific discovery. The dogs had learned that a lab coat meant food, and in response, they salivated every time they saw a lab assistant. In other words, the dogs had been conditioned to respond a certain way. From this point on, Pavlov decided to devote himself to the study of conditioning.

Pavlov tested his theories in the lab using a variety of neural stimuli. For example, he used electric shocks, a buzzer that produced specific tones and the ticking of a metronome to make the dogs associate certain noises and stimuli with food. He found that not only could he cause a conditioned response (salivation), he could also break the association if he made these same noises but did not give the dogs food.

Even though he was not a psychologist, Pavlov suspected that his findings could be applied to humans as well. He believed that a conditioned response may be causing certain behaviors in people with psychological problems and that these responses could be unlearned. Other scientists, such as John B. Watson, proved this theory correct when they were able to replicate Pavlov's research with humans. 

Pavlov worked in the lab until his death at the age of 86. He died on February 27, 1936, in Leningrad (now St. Petersburg), Russia after contracting double pneumonia. His death was commemorated with a grand funeral and a monument that was erected in his home country in his honor. His laboratory was also turned into a museum.

Legacy and Impact

Pavlov was a physiologist, but his legacy is primarily recognized in psychology and educational theory. By proving the existence of conditioned and non-conditioned reflexes, Pavlov provided a foundation for the study of behaviorism. Many renowned psychologists, including John B. Watson and  B. F. Skinner , were inspired by his work and built on it to gain a better understanding of behavior and learning.

To this day, nearly every student of psychology studies Pavlov's experiments to gain a better understanding of the scientific method , experimental psychology, conditioning, and behavioral theory. Pavlov's legacy can also be seen in popular culture in books like Aldous Huxley's " Brave New World ", which contained elements of Pavlovian conditioning.

• Cavendish, Richard. “Death of Ivan Pavlov.” History Today .
• Gantt, W. Horsley. “ Ivan Petrovich Pavlov. ” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 Feb. 2018.
• McLeod, Saul. “Pavlov's Dogs.” Simply Psychology, 2013 .
• Tallis, Raymond. “The Life of Ivan Pavlov.” The Wall Street Journal, 14 Nov. 2014 .
• “Ivan Pavlov - Biographical.” Nobelprize.org .
• “Ivan Pavlov.” PBS, Public Broadcasting Service .
• What Is a Conditioned Response?
• What Is an Unconditioned Response?
• What Is Classical Conditioning?
• What Is Behaviorism in Psychology?
• What Is Operant Conditioning? Definition and Examples
• What Is the Law of Effect in Psychology?
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• What Is the Premack Principle? Definition and Examples
• How Psychology Defines and Explains Deviant Behavior
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• Parasocial Relationships: Definition, Examples, and Key Studies
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• What Makes the “Uncanny Valley” So Unsettling?
• What Is Socioemotional Selectivity Theory?
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• Cultivation Theory

• Psychology class

Conditioning and Learning

University of Vermont

Basic principles of learning are always operating and always influencing human behavior. This module discusses the two most fundamental forms of learning -- classical (Pavlovian) and instrumental (operant) conditioning. Through them, we respectively learn to associate 1) stimuli in the environment, or 2) our own behaviors, with significant events, such as rewards and punishments. The two types of learning have been intensively studied because they have powerful effects on behavior, and because they provide methods that allow scientists to analyze learning processes rigorously. This module describes some of the most important things you need to know about classical and instrumental conditioning, and it illustrates some of the many ways they help us understand normal and disordered behavior in humans. The module concludes by introducing the concept of observational learning, which is a form of learning that is largely distinct from classical and operant conditioning.

• Associative learning
• Classical conditioning
• Instrumental learning
• Learning theory
• Operant conditioning
• Pavlovian learning
• Learning Objectives
• Distinguish between classical (Pavlovian) conditioning and instrumental (operant) conditioning.
• Understand some important facts about each that tell us how they work.
• Understand how they work separately and together to influence human behavior in the world outside the laboratory.
• Students will be able to list the four aspects of observational learning according to Social Learning Theory.

Two Types of Conditioning

Although Ivan Pavlov won a Nobel Prize for studying digestion, he is much more famous for something else: working with a dog, a bell, and a bowl of saliva. Many people are familiar with the classic study of “Pavlov’s dog,” but rarely do they understand the significance of its discovery. In fact, Pavlov’s work helps explain why some people get anxious just looking at a crowded bus, why the sound of a morning alarm is so hated, and even why we swear off certain foods we’ve only tried once. Classical (or Pavlovian) conditioning is one of the fundamental ways we learn about the world around us. But it is far more than just a theory of learning; it is also arguably a theory of identity. For, once you understand classical conditioning, you’ll recognize that your favorite music, clothes, even political candidate, might all be a result of the same process that makes a dog drool at the sound of bell.

Around the turn of the 20th century, scientists who were interested in understanding the behavior of animals and humans began to appreciate the importance of two very basic forms of learning. One, which was first studied by the Russian physiologist Ivan Pavlov, is known as classical , or Pavlovian conditioning . In his famous experiment, Pavlov rang a bell and then gave a dog some food. After repeating this pairing multiple times, the dog eventually treated the bell as a signal for food, and began salivating in anticipation of the treat. This kind of result has been reproduced in the lab using a wide range of signals (e.g., tones, light, tastes, settings) paired with many different events besides food (e.g., drugs, shocks, illness; see below). 

We now believe that this same learning process is engaged, for example, when humans associate a drug they’ve taken with the environment in which they’ve taken it; when they associate a stimulus (e.g., a symbol for vacation, like a big beach towel) with an emotional event (like a burst of happiness); and when they associate the flavor of a food with getting food poisoning. Although classical conditioning may seem “old” or “too simple” a theory, it is still widely studied today for at least two reasons: First, it is a straightforward test of associative learning that can be used to study other, more complex behaviors. Second, because classical conditioning is always occurring in our lives, its effects on behavior have important implications for understanding normal and disordered behavior in humans.

In a general way, classical conditioning occurs whenever neutral stimuli are associated with psychologically significant events. With food poisoning, for example, although having fish for dinner may not normally be something to be concerned about (i.e., a “neutral stimuli”), if it causes you to get sick, you will now likely associate that neutral stimuli (the fish) with the psychologically significant event of getting sick. These paired events are often described using terms that can be applied to any situation. 

The dog food in Pavlov’s experiment is called the unconditioned stimulus (US) because it elicits an unconditioned response (UR) . That is, without any kind of “training” or “teaching,” the stimulus produces a natural or instinctual reaction. In Pavlov’s case, the food (US) automatically makes the dog drool (UR). Other examples of unconditioned stimuli include loud noises (US) that startle us (UR), or a hot shower (US) that produces pleasure (UR).

On the other hand, a conditioned stimulus produces a conditioned response. A conditioned stimulus (CS) is a signal that has no importance to the organism until it is paired with something that does have importance. For example, in Pavlov’s experiment, the bell is the conditioned stimulus. Before the dog has learned to associate the bell (CS) with the presence of food (US), hearing the bell means nothing to the dog. However, after multiple pairings of the bell with the presentation of food, the dog starts to drool at the sound of the bell. This drooling in response to the bell is the conditioned response (CR) . Although it can be confusing, the conditioned response is almost always the same as the unconditioned response. However, it is called the conditioned response because it is conditional on (or, depends on) being paired with the conditioned stimulus (e.g., the bell). To help make this clearer, consider becoming really hungry when you see the logo for a fast food restaurant. There’s a good chance you’ll start salivating. Although it is the actual eating of the food (US) that normally produces the salivation (UR), simply seeing the restaurant’s logo (CS) can trigger the same reaction (CR).

Another example you are probably very familiar with involves your alarm clock. If you’re like most people, waking up early usually makes you unhappy. In this case, waking up early (US) produces a natural sensation of grumpiness (UR). Rather than waking up early on your own, though, you likely have an alarm clock that plays a tone to wake you. Before setting your alarm to that particular tone, let’s imagine you had neutral feelings about it (i.e., the tone had no prior meaning for you). However, now that you use it to wake up every morning, you psychologically “pair” that tone (CS) with your feelings of grumpiness in the morning (UR). After enough pairings, this tone (CS) will automatically produce your natural response of grumpiness (CR). Thus, this linkage between the unconditioned stimulus (US; waking up early) and the conditioned stimulus (CS; the tone) is so strong that the unconditioned response (UR; being grumpy) will become a conditioned response (CR; e.g., hearing the tone at any point in the day—whether waking up or walking down the street—will make you grumpy). Modern studies of classical conditioning use a very wide range of CSs and USs and measure a wide range of conditioned responses.

Although classical conditioning is a powerful explanation for how we learn many different things, there is a second form of conditioning that also helps explain how we learn. First studied by Edward Thorndike, and later extended by B. F. Skinner, this second type of conditioning is known as instrumental or operant conditioning . Operant conditioning occurs when a behavior (as opposed to a stimulus) is associated with the occurrence of a significant event. In the best-known example, a rat in a laboratory learns to press a lever in a cage (called a “Skinner box”) to receive food. Because the rat has no “natural” association between pressing a lever and getting food, the rat has to learn this connection. At first, the rat may simply explore its cage, climbing on top of things, burrowing under things, in search of food. Eventually while poking around its cage, the rat accidentally presses the lever, and a food pellet drops in. This voluntary behavior is called an operant behavior, because it “operates” on the environment (i.e., it is an action that the animal itself makes). 

Now, once the rat recognizes that it receives a piece of food every time it presses the lever, the behavior of lever-pressing becomes reinforced. That is, the food pellets serve as reinforcer s because they strengthen the rat’s desire to engage with the environment in this particular manner. In a parallel example, imagine that you’re playing a street-racing video game. As you drive through one city course multiple times, you try a number of different streets to get to the finish line. On one of these trials, you discover a shortcut that dramatically improves your overall time. You have learned this new path through operant conditioning. That is, by engaging with your environment (operant responses), you performed a sequence of behaviors that that was positively reinforced (i.e., you found the shortest distance to the finish line). And now that you’ve learned how to drive this course, you will perform that same sequence of driving behaviors (just as the rat presses on the lever) to receive your reward of a faster finish.

Operant conditioning research studies how the effects of a behavior influence the probability that it will occur again. For example, the effects of the rat’s lever-pressing behavior (i.e., receiving a food pellet) influences the probability that it will keep pressing the lever. For, according to Thorndike’s law of effect , when a behavior has a positive (satisfying) effect or consequence, it is likely to be repeated in the future. However, when a behavior has a negative (painful/annoying) consequence, it is less likely to be repeated in the future. Effects that increase behaviors are referred to as reinforcers, and effects that decrease them are referred to as punishers . 

An everyday example that helps to illustrate operant conditioning is striving for a good grade in class—which could be considered a reward for students (i.e., it produces a positive emotional response). In order to get that reward (similar to the rat learning to press the lever), the student needs to modify his/her behavior. For example, the student may learn that speaking up in class gets him/her participation points (a reinforcer), so the student speaks up repeatedly. However, the student also learns that s/he shouldn’t speak up about just anything; talking about topics unrelated to school actually costs points. Therefore, through the student’s freely chosen behaviors, s/he learns which behaviors are reinforced and which are punished.

An important distinction of operant conditioning is that it provides a method for studying how consequences influence “voluntary” behavior. The rat’s decision to press the lever is voluntary, in the sense that the rat is free to make and repeat that response whenever it wants. Classical conditioning, on the other hand, is just the opposite—depending instead on “involuntary” behavior (e.g., the dog doesn’t choose to drool; it just does). So, whereas the rat must actively participate and perform some kind of behavior to attain its reward, the dog in Pavlov’s experiment is a passive participant. One of the lessons of operant conditioning research, then, is that voluntary behavior is strongly influenced by its consequences.

The illustration above summarizes the basic elements of classical and instrumental conditioning. The two types of learning differ in many ways. However, modern thinkers often emphasize the fact that they differ—as illustrated here—in what is learned. In classical conditioning, the animal behaves as if it has learned to associate a stimulus with a significant event. In operant conditioning, the animal behaves as if it has learned to associate a behavior with a significant event. Another difference is that the response in the classical situation (e.g., salivation) is elicited by a stimulus that comes before it, whereas the response in the operant case is not elicited by any particular stimulus. Instead, operant responses are said to be emitted . The word “emitted” further conveys the idea that operant behaviors are essentially voluntary in nature.

Understanding classical and operant conditioning provides psychologists with many tools for understanding learning and behavior in the world outside the lab. This is in part because the two types of learning occur continuously throughout our lives. It has been said that “much like the laws of gravity, the laws of learning are always in effect” ( Spreat & Spreat, 1982 ).

Useful Things to Know about Classical Conditioning

Classical conditioning has many effects on behavior.

A classical CS (e.g., the bell) does not merely elicit a simple, unitary reflex. Pavlov emphasized salivation because that was the only response he measured. But his bell almost certainly elicited a whole system of responses that functioned to get the organism ready for the upcoming US (food) (see Timberlake, 2001 ). For example, in addition to salivation, CSs (such as the bell) that signal that food is near also elicit the secretion of gastric acid, pancreatic enzymes, and insulin (which gets blood glucose into cells). All of these responses prepare the body for digestion. Additionally, the CS elicits approach behavior and a state of excitement. And presenting a CS for food can also cause animals whose stomachs are full to eat more food if it is available. In fact, food CSs are so prevalent in modern society, humans are likewise inclined to eat or feel hungry in response to cues associated with food, such as the sound of a bag of potato chips opening, the sight of a well-known logo (e.g., Coca-Cola), or the feel of the couch in front of the television.

Classical conditioning is also involved in other aspects of eating. Flavors associated with certain nutrients (such as sugar or fat) can become preferred without arousing any awareness of the pairing. For example, protein is a US that your body automatically craves more of once you start to consume it (UR): since proteins are highly concentrated in meat, the flavor of meat becomes a CS (or cue, that proteins are on the way), which perpetuates the cycle of craving for yet more meat (this automatic bodily reaction now a CR).  

In a similar way, flavors associated with stomach pain or illness become avoided and dis liked. For example, a person who gets sick after drinking too much tequila may acquire a profound dislike of the taste and odor of tequila—a phenomenon called taste aversion conditioning . The fact that flavors are often associated with so many consequences of eating is important for animals (including rats and humans) that are frequently exposed to new foods. And it is clinically relevant. For example, drugs used in chemotherapy often make cancer patients sick. As a consequence, patients often acquire aversions to foods eaten just before treatment, or even aversions to such things as the waiting room of the chemotherapy clinic itself (see Bernstein, 1991 ; Scalera & Bavieri, 2009 ).

Classical conditioning occurs with a variety of significant events. If an experimenter sounds a tone just before applying a mild shock to a rat’s feet, the tone will elicit fear or anxiety after one or two pairings. Similar fear conditioning plays a role in creating many anxiety disorders in humans, such as phobias and panic disorders, where people associate cues (such as closed spaces, or a shopping mall) with panic or other emotional trauma (see Mineka & Zinbarg, 2006 ). Here, rather than a physical response (like drooling), the CS triggers an emotion. 

Another interesting effect of classical conditioning can occur when we ingest drugs. That is, when a drug is taken, it can be associated with the cues that are present at the same time (e.g., rooms, odors, drug paraphernalia). In this regard, if someone associates a particular smell with the sensation induced by the drug, whenever that person smells the same odor afterward, it may cue responses (physical and/or emotional) related to taking the drug itself. But drug cues have an even more interesting property: They elicit responses that often “compensate” for the upcoming effect of the drug (see Siegel, 1989 ). For example, morphine itself suppresses pain; however, if someone is used to taking morphine, a cue that signals the “drug is coming soon” can actually make the person more sensitive to pain. Because the person knows a pain suppressant will soon be administered, the body becomes more sensitive, anticipating that “the drug will soon take care of it.” Remarkably, such conditioned compensatory responses in turn decrease the impact of the drug on the body—because the body has become more sensitive to pain.

This conditioned compensatory response has many implications. For instance, a drug user will be most “tolerant” to the drug in the presence of cues that have been associated with it (because such cues elicit compensatory responses). As a result, overdose is usually not due to an increase in dosage, but to taking the drug in a new place without the familiar cues—which would have otherwise allowed the user to tolerate the drug (see  Siegel, Hinson, Krank, & McCully, 1982 ). Conditioned compensatory responses (which include heightened pain sensitivity and decreased body temperature, among others) might also cause discomfort, thus motivating the drug user to continue usage of the drug to reduce them. This is one of several ways classical conditioning might be a factor in drug addiction and dependence.

A final effect of classical cues is that they motivate ongoing operant behavior (see Balleine, 2005 ). For example, if a rat has learned via operant conditioning that pressing a lever will give it a drug, in the presence of cues that signal the “drug is coming soon” (like the sound of the lever squeaking), the rat will work harder to press the lever than if those cues weren’t present (i.e., there is no squeaking lever sound). Similarly, in the presence of food-associated cues (e.g., smells), a rat (or an overeater) will work harder for food. And finally, even in the presence of negative cues (like something that signals fear), a rat, a human, or any other organism will work harder to avoid those situations that might lead to trauma. Classical CSs thus have many effects that can contribute to significant behavioral phenomena.

The Learning Process

As mentioned earlier, classical conditioning provides a method for studying basic learning processes. Somewhat counterintuitively, though, studies show that pairing a CS and a US together is not sufficient for an association to be learned between them. Consider an effect called blocking (see Kamin, 1969 ). In this effect, an animal first learns to associate one CS—call it stimulus A—with a US. In the illustration above, the sound of a bell (stimulus A) is paired with the presentation of food. Once this association is learned, in a second phase, a second stimulus—stimulus B—is presented alongside stimulus A, such that the two stimuli are paired with the US together. In the illustration, a light is added and turned on at the same time the bell is rung. However, because the animal has already learned the association between stimulus A (the bell) and the food, the animal doesn’t learn an association between stimulus B (the light) and the food. That is, the conditioned response only occurs during the presentation of stimulus A, because the earlier conditioning of A “blocks” the conditioning of B when B is added to A. The reason? Stimulus A already predicts the US, so the US is not surprising when it occurs with Stimulus B.

Learning depends on such a surprise, or a discrepancy between what occurs on a conditioning trial and what is already predicted by cues that are present on the trial. To learn something through classical conditioning, there must first be some prediction error , or the chance that a conditioned stimulus won’t lead to the expected outcome. With the example of the bell and the light, because the bell always leads to the reward of food, there’s no “prediction error” that the addition of the light helps to correct. However, if the researcher suddenly requires that the bell and the light both occur in order to receive the food, the bell alone will produce a prediction error that the animal has to learn.

Blocking and other related effects indicate that the learning process tends to take in the most valid predictors of significant events and ignore the less useful ones. This is common in the real world. For example, imagine that your supermarket puts big star-shaped stickers on products that are on sale. Quickly, you learn that items with the big star-shaped stickers are cheaper. However, imagine you go into a similar supermarket that not only uses these stickers, but also uses bright orange price tags to denote a discount. Because of blocking (i.e., you already know that the star-shaped stickers indicate a discount), you don’t have to learn the color system, too. The star-shaped stickers tell you everything you need to know (i.e. there’s no prediction error for the discount), and thus the color system is irrelevant. 

Classical conditioning is strongest if the CS and US are intense or salient. It is also best if the CS and US are relatively new and the organism hasn’t been frequently exposed to them before. And it is especially strong if the organism’s biology has prepared it to associate a particular CS and US. For example, rats and humans are naturally inclined to associate an illness with a flavor, rather than with a light or tone. Because foods are most commonly experienced by taste, if there is a particular food that makes us ill, associating the flavor (rather than the appearance—which may be similar to other foods) with the illness will more greatly ensure we avoid that food in the future, and thus avoid getting sick. This sorting tendency, which is set up by evolution, is called  preparedness .

There are many factors that affect the strength of classical conditioning, and these have been the subject of much research and theory (see Rescorla & Wagner, 1972 ; Pearce & Bouton, 2001 ). Behavioral neuroscientists have also used classical conditioning to investigate many of the basic brain processes that are involved in learning (see Fanselow & Poulos, 2005 ; Thompson & Steinmetz, 2009 ).

Erasing Classical Learning

After conditioning, the response to the CS can be eliminated if the CS is presented repeatedly without the US. This effect is called extinction , and the response is said to become “extinguished.” For example, if Pavlov kept ringing the bell but never gave the dog any food afterward, eventually the dog’s CR (drooling) would no longer happen when it heard the CS (the bell), because the bell would no longer be a predictor of food. Extinction is important for many reasons. For one thing, it is the basis for many therapies that clinical psychologists use to eliminate maladaptive and unwanted behaviors. Take the example of a person who has a debilitating fear of spiders: one approach might include systematic exposure to spiders. Whereas, initially the person has a CR (e.g., extreme fear) every time s/he sees the CS (e.g., the spider), after repeatedly being shown pictures of spiders in neutral conditions, pretty soon the CS no longer predicts the CR (i.e., the person doesn’t have the fear reaction when seeing spiders, having learned that spiders no longer serve as a “cue” for that fear). Here, repeated exposure to spiders without an aversive consequence causes extinction.

Psychologists must accept one important fact about extinction, however: it does not necessarily destroy the original learning (see Bouton, 2004 ). For example, imagine you strongly associate the smell of chalkboards with the agony of middle school detention. Now imagine that, after years of encountering chalkboards, the smell of them no longer recalls the agony of detention (an example of extinction). However, one day, after entering a new building for the first time, you suddenly catch a whiff of a chalkboard and WHAM!, the agony of detention returns. This is called spontaneous recovery : following a lapse in exposure to the CS after extinction has occurred, sometimes re-exposure to the CS (e.g., the smell of chalkboards) can evoke the CR again (e.g., the agony of detention).

Another related phenomenon is the renewal effect : After extinction, if the CS is tested in a new context , such as a different room or location, the CR can also return. In the chalkboard example, the action of entering a new building—where you don’t expect to smell chalkboards—suddenly renews the sensations associated with detention. These effects have been interpreted to suggest that extinction inhibits rather than erases the learned behavior, and this inhibition is mainly expressed in the context in which it is learned (see “context” in the Key Vocabulary section below).

This does not mean that extinction is a bad treatment for behavior disorders. Instead, clinicians can increase its effectiveness by using basic research on learning to help defeat these relapse effects (see Craske et al., 2008 ). For example, conducting extinction therapies in contexts where patients might be most vulnerable to relapsing (e.g., at work), might be a good strategy for enhancing the therapy’s success.

Useful Things to Know about Instrumental Conditioning

Most of the things that affect the strength of classical conditioning also affect the strength of instrumental learning—whereby we learn to associate our actions with their outcomes. As noted earlier, the “bigger” the reinforcer (or punisher), the stronger the learning. And, if an instrumental behavior is no longer reinforced, it will also be extinguished. Most of the rules of associative learning that apply to classical conditioning also apply to instrumental learning, but other facts about instrumental learning are also worth knowing.

Instrumental Responses Come Under Stimulus Control

As you know, the classic operant response in the laboratory is lever-pressing in rats, reinforced by food. However, things can be arranged so that lever-pressing only produces pellets when a particular stimulus is present. For example, lever-pressing can be reinforced only when a light in the Skinner box is turned on; when the light is off, no food is released from lever-pressing. The rat soon learns to discriminate between the light-on and light-off conditions, and presses the lever only in the presence of the light (responses in light-off are extinguished). In everyday life, think about waiting in the turn lane at a traffic light. Although you know that green means go, only when you have the green arrow do you turn. In this regard, the operant behavior is now said to be under stimulus control . And, as is the case with the traffic light, in the real world, stimulus control is probably the rule.

The stimulus controlling the operant response is called a discriminative stimulus . It can be associated directly with the response, or the reinforcer (see below). However, it usually does not elicit the response the way a classical CS does. Instead, it is said to “set the occasion for” the operant response. For example, a canvas put in front of an artist does not elicit painting behavior or compel her to paint. It allows, or sets the occasion for, painting to occur.

Stimulus-control techniques are widely used in the laboratory to study perception and other psychological processes in animals. For example, the rat would not be able to respond appropriately to light-on and light-off conditions if it could not see the light. Following this logic, experiments using stimulus-control methods have tested how well animals see colors, hear ultrasounds, and detect magnetic fields. That is, researchers pair these discriminative stimuli with those they know the animals already understand (such as pressing the lever). In this way, the researchers can test if the animals can learn to press the lever only when an ultrasound is played, for example.

These methods can also be used to study “higher” cognitive processes. For example, pigeons can learn to peck at different buttons in a Skinner box when pictures of flowers, cars, chairs, or people are shown on a miniature TV screen (see Wasserman, 1995 ). Pecking button 1 (and no other) is reinforced in the presence of a flower image, button 2 in the presence of a chair image, and so on. Pigeons can learn the discrimination readily, and, under the right conditions, will even peck the correct buttons associated with pictures of new flowers, cars, chairs, and people they have never seen before. The birds have learned to categorize the sets of stimuli. Stimulus-control methods can be used to study how such categorization is learned.

Operant Conditioning Involves Choice

Another thing to know about operant conditioning is that the response always requires choosing one behavior over others. The student who goes to the bar on Thursday night chooses to drink instead of staying at home and studying. The rat chooses to press the lever instead of sleeping or scratching its ear in the back of the box. The alternative behaviors are each associated with their own reinforcers. And the tendency to perform a particular action depends on both the reinforcers earned for it and the reinforcers earned for its alternatives.

To investigate this idea, choice has been studied in the Skinner box by making two levers available for the rat (or two buttons available for the pigeon), each of which has its own reinforcement or payoff rate. A thorough study of choice in situations like this has led to a rule called the quantitative law of effect (see Herrnstein, 1970 ), which can be understood without going into quantitative detail: The law acknowledges the fact that the effects of reinforcing one behavior depend crucially on how much reinforcement is earned for the behavior’s alternatives. For example, if a pigeon learns that pecking one light will reward two food pellets, whereas the other light only rewards one, the pigeon will only peck the first light. However, what happens if the first light is more strenuous to reach than the second one? Will the cost of energy outweigh the bonus of food? Or will the extra food be worth the work? In general, a given reinforcer will be less reinforcing if there are many alternative reinforcers in the environment. For this reason, alcohol, sex, or drugs may be less powerful reinforcers if the person’s environment is full of other sources of reinforcement, such as achievement at work or love from family members.

Cognition in Instrumental Learning

Modern research also indicates that reinforcers do more than merely strengthen or “stamp in” the behaviors they are a consequence of, as was Thorndike’s original view. Instead, animals learn about the specific consequences of each behavior, and will perform a behavior depending on how much they currently want—or “value”—its consequence.

This idea is best illustrated by a phenomenon called the reinforcer devaluation effect (see Colwill & Rescorla, 1986 ). A rat is first trained to perform two instrumental actions (e.g., pressing a lever on the left, and on the right), each paired with a different reinforcer (e.g., a sweet sucrose solution, and a food pellet). At the end of this training, the rat tends to press both levers, alternating between the sucrose solution and the food pellet. In a second phase, one of the reinforcers (e.g., the sucrose) is then separately paired with illness. This conditions a taste aversion to the sucrose. In a final test, the rat is returned to the Skinner box and allowed to press either lever freely. No reinforcers are presented during this test (i.e., no sucrose or food comes from pressing the levers), so behavior during testing can only result from the rat’s memory of what it has learned earlier. Importantly here, the rat chooses not to perform the response that once produced the reinforcer that it now has an aversion to (e.g., it won’t press the sucrose lever). This means that the rat has learned and remembered the reinforcer associated with each response, and can combine that knowledge with the knowledge that the reinforcer is now “bad.” Reinforcers do not merely stamp in responses; the animal learns much more than that. The behavior is said to be “ goal-directed ” (see Dickinson & Balleine, 1994 ), because it is influenced by the current value of its associated goal (i.e., how much the rat wants/doesn’t want the reinforcer).

Things can get more complicated, however, if the rat performs the instrumental actions frequently and repeatedly. That is, if the rat has spent many months learning the value of pressing each of the levers, the act of pressing them becomes automatic and routine. And here, this once goal-directed action (i.e., the rat pressing the lever for the goal of getting sucrose/food) can become a habit . Thus, if a rat spends many months performing the lever-pressing behavior (turning such behavior into a habit), even when sucrose is again paired with illness, the rat will continue to press that lever (see Holland, 2004 ). After all the practice, the instrumental response (pressing the lever) is no longer sensitive to reinforcer devaluation. The rat continues to respond automatically, regardless of the fact that the sucrose from this lever makes it sick. 

Habits are very common in human experience, and can be useful. You do not need to relearn each day how to make your coffee in the morning or how to brush your teeth. Instrumental behaviors can eventually become habitual, letting us get the job done while being free to think about other things.

Putting Classical and Instrumental Conditioning Together

Classical and operant conditioning are usually studied separately. But outside of the laboratory they almost always occur at the same time. For example, a person who is reinforced for drinking alcohol or eating excessively learns these behaviors in the presence of certain stimuli—a pub, a set of friends, a restaurant, or possibly the couch in front of the TV. These stimuli are also available for association with the reinforcer. In this way, classical and operant conditioning are always intertwined.

The figure below summarizes this idea, and helps review what we have discussed in this module. Generally speaking, any reinforced or punished operant response (R) is paired with an outcome (O) in the presence of some stimulus or set of stimuli (S).

The figure illustrates the types of associations that can be learned in this very general scenario. For one thing, the organism will learn to associate the response and the outcome (R – O). This is instrumental conditioning. The learning process here is probably similar to classical conditioning, with all its emphasis on surprise and prediction error. And, as we discussed while considering the reinforcer devaluation effect, once R – O is learned, the organism will be ready to perform the response if the outcome is desired or valued. The value of the reinforcer can also be influenced by other reinforcers earned for other behaviors in the situation. These factors are at the heart of instrumental learning.

Second, the organism can also learn to associate the stimulus with the reinforcing outcome (S – O). This is the classical conditioning component, and as we have seen, it can have many consequences on behavior. For one thing, the stimulus will come to evoke a system of responses that help the organism prepare for the reinforcer (not shown in the figure): The drinker may undergo changes in body temperature; the eater may salivate and have an increase in insulin secretion. In addition, the stimulus will evoke approach (if the outcome is positive) or retreat (if the outcome is negative). Presenting the stimulus will also prompt the instrumental response.

The third association in the diagram is the one between the stimulus and the response (S – R). As discussed earlier, after a lot of practice, the stimulus may begin to elicit the response directly. This is habit learning, whereby the response occurs relatively automatically, without much mental processing of the relation between the action and the outcome and the outcome’s current value.

The final link in the figure is between the stimulus and the response-outcome association [S – (R – O)]. More than just entering into a simple association with the R or the O, the stimulus can signal that the R – O relationship is now in effect. This is what we mean when we say that the stimulus can “set the occasion” for the operant response: It sets the occasion for the response-reinforcer relationship. Through this mechanism, the painter might begin to paint when given the right tools and the opportunity enabled by the canvas. The canvas theoretically signals that the behavior of painting will now be reinforced by positive consequences.

The figure provides a framework that you can use to understand almost any learned behavior you observe in yourself, your family, or your friends. If you would like to understand it more deeply, consider taking a course on learning in the future, which will give you a fuller appreciation of how classical learning, instrumental learning, habit learning, and occasion setting actually work and interact.

Observational Learning

Not all forms of learning are accounted for entirely by classical and operant conditioning. Imagine a child walking up to a group of children playing a game on the playground. The game looks fun, but it is new and unfamiliar. Rather than joining the game immediately, the child opts to sit back and watch the other children play a round or two. Observing the others, the child takes note of the ways in which they behave while playing the game. By watching the behavior of the other kids, the child can figure out the rules of the game and even some strategies for doing well at the game. This is called observational learning .

Observational learning is a component of Albert Bandura’s Social Learning Theory ( Bandura, 1977 ), which posits that individuals can learn novel responses via observation of key others’ behaviors. Observational learning does not necessarily require reinforcement, but instead hinges on the presence of others, referred to as social models . Social models are typically of higher status or authority compared to the observer, examples of which include parents, teachers, and police officers. In the example above, the children who already know how to play the game could be thought of as being authorities—and are therefore social models—even though they are the same age as the observer. By observing how the social models behave, an individual is able to learn how to act in a certain situation. Other examples of observational learning might include a child learning to place her napkin in her lap by watching her parents at the dinner table, or a customer learning where to find the ketchup and mustard after observing other customers at a hot dog stand.

Bandura theorizes that the observational learning process consists of four parts. The first is attention —as, quite simply, one must pay attention to what s/he is observing in order to learn. The second part is retention : to learn one must be able to retain the behavior s/he is observing in memory.The third part of observational learning, initiation , acknowledges that the learner must be able to execute (or initiate) the learned behavior. Lastly, the observer must possess the motivation to engage in observational learning. In our vignette, the child must want to learn how to play the game in order to properly engage in observational learning.

Researchers have conducted countless experiments designed to explore observational learning, the most famous of which is Albert Bandura’s “Bobo doll experiment.”

In this experiment ( Bandura, Ross & Ross 1961 ), Bandura had children individually observe an adult social model interact with a clown doll (“Bobo”). For one group of children, the adult interacted aggressively with Bobo: punching it, kicking it, throwing it, and even hitting it in the face with a toy mallet. Another group of children watched the adult interact with other toys, displaying no aggression toward Bobo. In both instances the adult left and the children were allowed to interact with Bobo on their own. Bandura found that children exposed to the aggressive social model were significantly more likely to behave aggressively toward Bobo, hitting and kicking him, compared to those exposed to the non-aggressive model. The researchers concluded that the children in the aggressive group used their observations of the adult social model’s behavior to determine that aggressive behavior toward Bobo was acceptable.

While reinforcement was not required to elicit the children’s behavior in Bandura’s first experiment, it is important to acknowledge that consequences do play a role within observational learning. A future adaptation of this study ( Bandura, Ross, & Ross, 1963 ) demonstrated that children in the aggression group showed less aggressive behavior if they witnessed the adult model receive punishment for aggressing against Bobo. Bandura referred to this process as vicarious reinforcement , as the children did not experience the reinforcement or punishment directly, yet were still influenced by observing it.

We have covered three primary explanations for how we learn to behave and interact with the world around us. Considering your own experiences, how well do these theories apply to you? Maybe when reflecting on your personal sense of fashion, you realize that you tend to select clothes others have complimented you on (operant conditioning). Or maybe, thinking back on a new restaurant you tried recently, you realize you chose it because its commercials play happy music (classical conditioning). Or maybe you are now always on time with your assignments, because you saw how others were punished when they were late (observational learning). Regardless of the activity, behavior, or response, there’s a good chance your “decision” to do it can be explained based on one of the theories presented in this module. 

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• Discussion Questions
• Describe three examples of Pavlovian (classical) conditioning that you have seen in your own behavior, or that of your friends or family, in the past few days.
• Describe three examples of instrumental (operant) conditioning that you have seen in your own behavior, or that of your friends or family, in the past few days.
• Drugs can be potent reinforcers. Discuss how Pavlovian conditioning and instrumental conditioning can work together to influence drug taking.
• In the modern world, processed foods are highly available and have been engineered to be highly palatable and reinforcing. Discuss how Pavlovian and instrumental conditioning can work together to explain why people often eat too much.
• How does blocking challenge the idea that pairings of a CS and US are sufficient to cause Pavlovian conditioning? What is important in creating Pavlovian learning?
• How does the reinforcer devaluation effect challenge the idea that reinforcers merely “stamp in” the operant response? What does the effect tell us that animals actually learn in operant conditioning?
• With regards to social learning do you think people learn violence from observing violence in movies? Why or why not?
• What do you think you have learned through social learning? Who are your social models?
• Balleine, B. W. (2005). Neural basis of food-seeking: Affect, arousal, and reward in corticostratolimbic circuits. Physiology & Behavior, 86 , 717–730.
• Bandura, A. (1977). Social learning theory . Englewood Cliffs, NJ: Prentice Hall
• Bandura, A., Ross, D., Ross, S (1963). Imitation of film-mediated aggressive models. Journal of Abnormal and Social Psychology 66 (1), 3 - 11.
• Bandura, A.; Ross, D.; Ross, S. A. (1961). "Transmission of aggression through the imitation of aggressive models". Journal of Abnormal and Social Psychology 63 (3), 575–582.
• Bernstein, I. L. (1991). Aversion conditioning in response to cancer and cancer treatment. Clinical Psychology Review, 11 , 185–191.
• Bouton, M. E. (2004). Context and behavioral processes in extinction. Learning & Memory, 11 , 485–494.
• Colwill, R. M., & Rescorla, R. A. (1986). Associative structures in instrumental learning. In G. H. Bower (Ed.), The psychology of learning and motivation , (Vol. 20, pp. 55–104). New York, NY: Academic Press.
• Craske, M. G., Kircanski, K., Zelikowsky, M., Mystkowski, J., Chowdhury, N., & Baker, A. (2008). Optimizing inhibitory learning during exposure therapy. Behaviour Research and Therapy, 46 , 5–27.
• Dickinson, A., & Balleine, B. W. (1994). Motivational control of goal-directed behavior. Animal Learning & Behavior, 22 , 1–18.
• Fanselow, M. S., & Poulos, A. M. (2005). The neuroscience of mammalian associative learning. Annual Review of Psychology, 56 , 207–234.
• Herrnstein, R. J. (1970). On the law of effect. Journal of the Experimental Analysis of Behavior, 13, 243–266.
• Holland, P. C. (2004). Relations between Pavlovian-instrumental transfer and reinforcer devaluation. Journal of Experimental Psychology: Animal Behavior Processes, 30 , 104–117.
• Kamin, L. J. (1969). Predictability, surprise, attention, and conditioning. In B. A. Campbell & R. M. Church (Eds.), Punishment and aversive behavior (pp. 279–296). New York, NY: Appleton-Century-Crofts.
• Mineka, S., & Zinbarg, R. (2006). A contemporary learning theory perspective on the etiology of anxiety disorders: It’s not what you thought it was. American Psychologist, 61 , 10–26.
• Pearce, J. M., & Bouton, M. E. (2001). Theories of associative learning in animals. Annual Review of Psychology, 52 , 111–139.
• Rescorla, R. A., & Wagner, A. R. (1972). A theory of Pavlovian conditioning: Variations in the effectiveness of reinforcement and nonreinforcement. In A. H. Black & W. F. Prokasy (Eds.), Classical conditioning II: Current research and theory (pp. 64–99). New York, NY: Appleton-Century-Crofts.
• Scalera, G., & Bavieri, M. (2009). Role of conditioned taste aversion on the side effects of chemotherapy in cancer patients. In S. Reilly & T. R. Schachtman (Eds.), Conditioned taste aversion: Behavioral and neural processes (pp. 513–541). New York, NY: Oxford University Press.
• Siegel, S. (1989). Pharmacological conditioning and drug effects. In A. J. Goudie & M. Emmett-Oglesby (Eds.), Psychoactive drugs (pp. 115–180). Clifton, NY: Humana Press.
• Siegel, S., Hinson, R. E., Krank, M. D., & McCully, J. (1982). Heroin “overdose” death: Contribution of drug associated environmental cues. Science, 216 , 436–437.
• Spreat, S., & Spreat, S. R. (1982). Learning principles. In V. Voith & P. L. Borchelt (Eds.), Veterinary clinics of North America: Small animal practice (pp. 593–606). Philadelphia, PA: W. B. Saunders.
• Thompson, R. F., & Steinmetz, J. E. (2009). The role of the cerebellum in classical conditioningof discrete behavioral responses. Neuroscience, 162 , 732–755.
• Timberlake, W. L. (2001). Motivational modes in behavior systems. In R. R. Mowrer & S. B. Klein (Eds.), Handbook of contemporary learning theories (pp. 155–210). Mahwah, NJ: Lawrence Erlbaum Associates, Inc.
• Wasserman, E. A. (1995). The conceptual abilities of pigeons. American Scientist, 83 , 246–255.

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Behaviorism

An aged tortoise tells us much about pavlovian conditioning, pavlov's broad theory of behavioral adaptation was never just about salivation..

Posted August 29, 2024 | Reviewed by Michelle Quirk

• Most think that Pavlovian conditioning is a rudimentary form of learning limited to reflexes like salivation.
• Pavlov's own theory of signalization was far more encompassing.
• Signalization applied not only to reflexive consummatory responses, but to preparatory locomotor responses.

As he nears 200 years of age, Jonathan the tortoise has been receiving a great deal of international attention . However, longevity is not the only reason why we should find Jonathan to be of special interest. He’s confirming what Pavlov said about conditioning a century ago: It isn’t just about salivation!

Jonathan is a giant tortoise ( Aldabrachelys gigantea hololissa ) who, in 1882, was shipped from his original home in the Seychelles Islands in the Indian Ocean to Saint Helena—a volcanic tropical island and British Overseas Territory located in the South Atlantic Ocean some 1,200 miles off the west coast of Africa. Jonathan is estimated to be 192 years old, having “officially” hatched on December 4, 1832, making him the oldest living land animal according to the Guinness Book of World Records (Atwal, 2022). Jonathan turns out to be Saint Helena’s second most famous expatriate inhabitant, its first being Napoleon Bonaparte, who was exiled there in 1815 in the wake of his ignominious defeat at the Battle of Waterloo.

Jonathan is still in fine fettle despite his advanced age, thanks in great measure to the assiduous care he’s received for the past 15 years from veterinarian Joe Hollins. Although the nearly 400-pound chelonian has lost his senses of smell and sight, his hearing is quite acute. That enduring sense is crucial to the vital lesson Jonathan teaches us about Pavlovian conditioning.

Hollins has made a number of astute observations of Jonathan’s feeding activity: “He knows my voice and comes to me like a dog, but I have to accept it is mainly Pavlovian because he associates me with food” (Free, 2022). Further elaborating, Hollins stresses the fervor of Jonathan’s Pavlovian reactions: “He recognizes my voice when I approach and call to him softly. He literally jerks to attention and starts biting the air” (Free, 2024).

There’s no mystery as to how such Pavlovian conditioning has taken place. For many years, Hollins’ voice has consistently preceded Jonathan’s weekly repast of fresh fruit and vegetables—variously including bananas, apples, pears, carrots, cucumbers, cabbage, and hearts of lettuce—which supplement the giant tortoise’s far less delectable fare of grass and clover.

Now, by way of comparison, consider Pavlov’s (1934) characterization of the conditioned motor responses exhibited by his dogs:

"The first reaction elicited by the established conditioned stimulus usually consists in a movement towards the stimulus, i.e., the animal turns to the place where the stimulus is to be found. If the stimulus is within reach, the animal even tries to come in touch with it, namely, by means of its mouth. Thus, if the conditioned stimulus is the switching on of a lamp, the dog licks the lamp; if the conditioned stimulus is a sound the dog will even snap at the air (in case of very heightened food excitability)."

The resemblance between Pavlov’s description of his dogs’ conditioned responding and Hollins’s description of Jonathan’s conditioned responding is striking. What is also striking is that the specific behaviors being highlighted—orienting, approaching, and biting—are overtly directed toward the conditioned stimulus, whether it be visual or auditory.

So, what’s happened to that most exemplary of Pavlovian conditioned responses—salivation?

Nothing at all. Both dogs and tortoises avidly salivate and manipulate food in their mouths. Pavlov’s strong focus on salivation as the target response in much of his other scientific writings was the natural extension of his prior research in digestion, for which he was awarded the Nobel Prize in Physiology or Medicine in 1904. In addition, while conducting that work, Pavlov diligently devised highly accurate methods to measure secretory activity; similarly accurate measures were not then available to investigate motor activity. Finally, Pavlov dedicated himself to providing an entirely objective explanation of his pioneering findings. He firmly believed that focusing on dogs’ salivation would be more conducive to achieving this goal than would focusing on dogs’ directed motor responses for the simple reason that, in the case of secretory responses, there would probably be a “much smaller tendency to interpret them in an anthropomorphic fashion” (1927).

By integrating his meticulous measurements of salivary secretion with his more informal observations of directed motor activity, Pavlov was able to propose a comprehensive theory of associative conditioning. Here’s how Pavlov explained this theory: Although animals may be equipped by evolution with a host of generally adaptive inborn responses, many of those responses may not be suited to the specific environmental conditions that animals encounter in their everyday lives. Those particular conditions may demand more fine-tuning, which becomes the business of the brain—the bodily organ that can effectively and flexibly link adaptive behaviors with environmental stimuli. To this key function of the brain, Pavlov gave the name signalization , and to these experientially acquired signals, he gave the name conditioned stimuli (1927).

Pavlov’s laboratory experiments famously showed that “artificial” conditioned stimuli (such as a ticking metronome) that are arbitrarily paired with food, as well as “natural” conditioned stimuli (such as the smell and sight of food) that are ordinarily paired with food in the development of a dog’s normal feeding behavior, could each serve as highly effective signals. Indeed, in the latter case, Pavlov surprisingly documented that puppies do not unconditionally salivate to the smell or sight of foods like meat and bread; only after the puppies had previously eaten those foods did their smell or sight come to trigger salivation.

Pavlov had one more critical point to make about signalization. Yes, it is highly adaptive for the proximal presentation of food in the mouth to unconditionally stimulate copious quantities of saliva, and in so doing to promote swallowing and digestion. Of even greater importance, however, is for the distal presentation of a signaling stimulus to conditionally elicit the motor components of nutrition , thus instigating the pursuit of food (1927). After all, you can’t eat the food if you don’t first detect its presence, approach it, and then seize it. Hence comes Pavlov’s bold exclamation: “How many simple physiological reflexes start from the nose, the eye, and the ear, and therefore originate at a distance!” (1928).

In Pavlov’s theory of signalization, the movement reactions of animals are put front and center in a fully integrative analysis of adaptive behavior: “By means of distant and even accidental characteristics of objects the animal seeks his food, avoids his enemies, etc.” (1928).

As noted earlier, Jonathan has lost his senses of smell and sight. Yet, his still-functioning sense of hearing enables Jonathan to locate Hollins, to approach him, and, in a state of heightened food excitability, to bite at the air—just like Pavlov’s dogs.

Hatched some 17 years before Pavlov’s birth and living some 88 years after Pavlov’s death, Jonathan provides persuasive support for Pavlov’s theory of conditioned responding. Adaptive behaviors—both secretory and motor—can be refined by experiences that are unique to an individual animal through the participation of the distance receptors and the brain. Signalization thus represents the theoretical complement to Pavlov’s pioneering empirical investigations—a theory that makes it clear that Pavlovian conditioning was never just about salivation.

A version of this post also appears in the APS Observer.

Atwal, S. (2022, January 12). 190-year-old Jonathan becomes world’s oldest tortoise ever. Guinness World Records.

Free, C. (2022, January 30). The world’s oldest living land animal? At age 190, it’s Jonathan the tortoise. Washington Post .

Free, C. (2024, January 1). Happy 191st (or so) birthday to the world’s oldest living land animal. Washington Post .

Pavlov, I. P. (1927). Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex. Translated and edited by G. V. Anrep. Oxford University Press.

Pavlov, I. P. (1928). Lectures on Conditioned Reflexes: Twenty-Five Years of Objective Study of the Higher Nervous Activity (Behaviour) of Animals. (W. H. Gantt, Trans.). Liverwright Publishing Corporation. https://doi.org/10.1037/11081-000

Pavlov, I. P. (1934). An attempt at a physiological interpretation of obsessional neurosis and paranoia. Journal of Mental Science , 80 , 187–197. https://doi.org/10.1192/bjp.80.329.187-a

Ed Wasserman, Ph.D., studies learning, memory, and cognition at The University of Iowa.

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