Classical Conditioning: How It Works With Examples

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 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 which is unlearned (i.e., unconditioned) and therefore is a natural response which 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 which 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:

Now 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.

Little Albert Classical Conditioning

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 UCSwere 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.


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.

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 a still 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 it was paired with food.

Unconditioned Stimulus

In classical conditioning, the unconditioned stimulus is a feature of the environment that causes a natural and automatic unconditioned response. In Pavlov’s study, the unconditioned stimulus was food.

Unconditioned Response

In classical conditioning, an unconditioned response is an unlearned 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

In classical conditioning, the conditioned stimulus (CS) is a substitute stimulus that triggers the same response in an organism as an unconditioned stimulus.
For example, Pavlov’s dog learned to salivate at the sound of a bell. Simply put, a conditioned stimulus makes an organism react to something because it is associated with something else.

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.


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.

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.

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


In psychology, generalization is the tendency to respond in the same way to stimuli that are similar but not identical to the 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.


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.

Critical Evaluation

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).

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.

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).

But 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.

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

However, applying classical conditioning to our understanding of complex human behavior such as memory, thinking, reasoning or problem-solving has proved more problematic.

In normal adults, the conditioning process can apparently 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).

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.

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

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 to 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.

A final criticism of classical conditioning theory is that it is deterministic. This means that it does not allow for any degree of free will in the individual. 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 which can then 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.


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.

Logan, C. A. (2002). When scientific knowledge becomes scientific discovery: The disappearance of classical conditioning before PavlovJournal of the History of the Behavioral Sciences38(4), 393-403.

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

Watson, J. B. (1913). Psychology as the behaviorist views itPsychological Review, 20, 158–177.

Watson, J.B. (1913). Psychology as the behaviorist Views It. Psychological Review, 20, 158-177.

Watson, J. B. (1924). Behaviorism. New York: People’s Institute Publishing Company.

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

Olivia Guy-Evans

BSc (Hons), Psychology, MSc, Psychology of Education

Associate Editor for Simply Psychology

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

Saul Mcleod, PhD

Educator, Researcher

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

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.