Do you remember how eager for food you were every time you heard the end of class bell back when you were still in school?

Do you remember this one time when you were going back home through a dark alley and a dog started barking at you?

Do you remember how from that moment on you started avoiding the shortcut and took a detour even if you were longing for a bed for hours already?

These simple examples are just a brief notion of what lies ahead in this article.

Namely, we will try to present some basic elements of one of the psychological principles which was discovered by accident.

The human brain is a mighty network which is so complicated that even after decades of exploration, it is still a huge black hole that remains a mystery to most scientists.

Sometimes it all seems so simple.

Your brain controls your extremities, your eyes, your speech, even creativity (that, by the way, you can boost with some interesting techniques).

You see an input of sorts and you provide the necessary output. And definitely, this is the easy part.

But what happens in those cases as depicted in the beginning?

Why are we prone to associate a completely isolated (past) instance with future occurrences or internal fears?

Why do we keep thinking that we will get to eat every time we hear a bell ringing or that a dog will bark at us or attack us in the same dark alley?

This is the complicated part we were talking about. It is here that we are in the complete unknown. In this area, we are in the dark. The human brain has been the focus of attention of multiple studies.

One can study it from multiple perspectives such as neurobiological, psychological, or a simply physical aspect where you make an effort to treat a physical injury without leaving detrimental consequences to the other aspects.

From the neurobiological and psychological stance, things are everything but simple.

Again, the brain is an intricate network, so masterly woven that decades may pass and we will still know almost nothing about it.

However, according to the aforementioned, our brain inevitably creates and controls certain processes within us that for quite some time we were unable to understand.

The situation would have persisted had it not been for Ivan Petrovich Pavlov, a Russian psychologist who quite accidentally discovered an occurrence called classical conditioning.


As briefly mentioned in the Introduction, Ivan Petrovich Pavlov was a Russian psychologist who was born at the beginning of the 20th century.

At a certain point of his career, Pavlov was deeply interested in studying gastric system and with this aim he conducted his medical experiments on dogs.

Most surely, his main research made a significant contribution to gastric medicine and he was properly awarded for the results.

Still, this work of his also resulted in a by-product, which Pavlov decided not to neglect.

This by-product that Pavlov encountered by mere chance, is known as one of the most relevant predecessors of behavioural psychology today.

If we want to understand thoroughly why Pavlov’s work is so significant even in the 21st century, we need to bring to mind his experiment on dogs.

Namely, Pavlov was originally interested in learning how the gastric system of animals, and consequently humans, works and what the role of saliva and salivating was in food digestion.

To this end, Pavlov decided to study dogs in laboratory conditions.

As a consequence, dogs were kept in compartments and were given food regularly. Every time the dogs were presented with food, their glands would start producing saliva.

The dogs were observed and the quantity of saliva duly measured.

As time went by, Pavlov noticed that dogs eventually started salivating even before the food was placed in front of them.

Eventually, he realized how something else was causing the dogs’ glands to produce saliva, some external factor associated with the food, but still completely independent of it.

As it turned out, the laboratory staff members were bringing in the food for dogs, so every time the dogs would see a white coat, they would start salivating.

To confirm his theory, Pavlov later introduced various other triggers occurring before the food was brought in.

These were occurrences such as electric shocks, buzzing sounds, etc. that the dogs were exposed to before the actual eating.

And, as Pavlov suspected, the dogs developed an association between these and the feeding process so any time they were shocked or they heard the buzzer, their glands would begin to salivate.

While studying this theory even further, Pavlov discovered that the “accidental” and “unrelated” stimulus could also be un-learned.

Once he confirmed that shocks or sounds would cause the salivating process, he decided to see what happens if the process was reversed.

Namely, on multiple occasions he would shock the dogs, leaving the food out.

Finally, the dogs learned that shocks were not related to food in any case whatsoever.

As the shocks repeated and no food was placed in front of them, dogs first decreased the saliva amount and eventually stopped salivating completely.


Even though Pavlov’s intention was to study something completely different, he actually stumbled upon a very significant discovery.

This experiment on dogs showed how the animal brain creates a link between a completely unintentional instance with a completely intentional one.

Of course, some repetition was necessary, but the brain shortly “picked” up how white coat or buzzing was linked with the food and eating.

Despite the fact that the experiment was conducted on dogs, the conclusion is easily transferable to the human brain.

When we are exposed to some stimuli and a reaction follows – remember now the example of a dog barking at you in a dark alley – we are linking this stimulus to each future instance expecting and displaying the same reaction.


We have established that Pavlov’s experiment and research were purely accidental. However, they did light a spark in other scientists.

Namely, an American psychologist, John B. Watson resumed Pavlov’s work and moved to another direction.

His idea now was to confirm the occurrence of the same behaviour pattern in humans.

For this aim, he conducted an experiment which today would be rather unethical.

The experiment in question was conducted on a nine months old baby named Albert, which is why the experiment is today known as Little Albert Experiment.

Watson was trying to induce phobias from fury animals or objects in infants, so what he did was placing little Albert on a mattress and let it play with a white rat.

At first, Albert showed no signs of fear and would calmly play with the rat.

Later on, Watson moved on and started introducing loud and unpleasant sounds every time Albert would touch the rat.

As the situation repeated several times, the infant developed a fear of the rat and started crying every time the rat would show up even when the sound was left out.

Moreover, little Albert supposedly developed a phobia from all other furry animals and objects and not only rats.

Had it been different times, Watson would probably not be allowed to conduct an experiment as severe as that. Still, despite the fact that it was a highly unethical act, the experiment did confirm the same thesis Pavlov established with dogs.

The final conclusion was also that our mind starts creating links between a natural stimulus that the mind is supposed to focus on and environmental condition which is originally introduced by mere accident.


Today, classical conditioning is an acclaimed psychological theory which has developed even further after Pavlov’s original experiment and discovery, and some early stages of its development were depicted in the previous chapter.

1. Terms

As is the case in all fields of study, the theory demanded its own terminology.

For this purpose, certain phrases and terms were coined to help us precisely define the occurrences depicted in both Pavlov’s and Watson’s experiment.

The terms which are the essence of this theory are present below.

  1. Stimulus
  2. Response
  3. Unconditioned stimulus
  4. Conditioned stimulus
  5. Unconditioned response
  6. Conditioned response
  7. Generalisation

2. Definitions

Before we go further into defining and explaining each of these terms separately, let us focus on what classical conditioning is.

Classical conditioning is a form of subconscious learning where two independent stimuli are paired so as to produce a response. This is the process of learning by association.

The stimuli you, i.e. your brain, pair are the unconditioned and conditioned stimulus after which you produce a conditioned response.

To put it in simple terms, classical conditioning (also known as Pavlovian conditioning) means that two stimuli are linked together to produce a new learned response in a person or animal.

The stimulus is any feature of the environment, whether intentional or accidental, which triggers the response.

The response is virtually the reaction of the subject to the given stimuli, i.e. the behaviour induced by stimuli.

From our previous explanations, we can conclude that the unconditioned stimulus is the natural occurrence, the one we produced intentionally. It is a naturally occurring act, i.e. stimulus.

On the other hand, the conditioned stimulus is the unrelated act, at first, which leads to a response we were expecting to achieve by introducing the unconditioned stimulus.

This conditioned stimulus is the environmental stimulus, which is later deliberately linked with the neutral one. It only has an effect when linked with the unconditioned stimulus.

The unconditioned response is the original reaction to the unconditioned stimulus.

The conditioned response is the behaviour caused by the conditioned stimulus.

The generalisation is recreating conditioned response under stimuli similar to the original environmental stimulus.

Recovery is the un-learning process where the subject slowly goes back to the stage which does not include any environmental conditioning.

To make things a bit more clear, let us briefly re-create Pavlov’s experiment and break it down to simple steps.

At the same time, we will explain each of the terms by giving relevant examples from the experiment.

To summarize, Pavlov was studying the effect of saliva on food digestions in dogs. In order to achieve this, he had to give food to dogs.

Food, in this case, is the natural stimulus, i.e. the unconditioned stimulus. Upon seeing food, dogs start creating saliva through their glands.

The salivation process represents the unconditioned response here.

Now, if we introduce an environmental element to the story, for example, a bell – it will produce no response at first. However, if this neutral stimulus is combined with the unconditioned stimulus, it will lead to a response.

If we repeat it a sufficient number of times, i.e. if we pair the neutral stimulus with the unconditioned stimulus often enough, the bell ringing becomes our conditioned stimulus.

In each future instance, even when the food is absent, bell ringing will still cause salivating, which in this case becomes the conditioned response.

As for generalising here, let’s assume that the bell is slightly changed. For some time, the dog will still salivate, linking this sound to the one he had been used to.

Once we sever the links between the unconditioned and conditioned stimulus and present the subject with the conditioned stimulus only, the conditioned response will gradually subside until it completely disappears.

What might additionally help in understanding the links between different stimuli and different responses is the diagram below. It clearly shows the chronological and logical sequence of events causing dogs to salivate.

Pavlov's Experiment


From the example given above, we can conclude that classical conditioning consists of three consecutive stages.

During Stage 1, the unconditioned stimulus produces an unconditioned response.

To put it simply, a stimulus causes a response, or behaviour, which is unconditioned, or unlearned.

During this stage the neutral stimulus is present, but still, his effect is not observed, i.e. recognized.

In Stage 2, the neutral stimulus gets associated with the unconditioned stimulus and thus becomes the conditioned stimulus. In order to be fully recognized, the conditioned stimulus needs to happen prior, or simultaneously, to the unconditioned stimulus.

During Stage 3, the conditioned and unconditioned stimulus are fully linked one with another and together they create a new conditioned response.


Even though examples of classical conditioning we described previously were purely experimental, this is the phenomenon we encounter on a daily basis.

This is again the time to remind ourselves of the brief examples given in the introductory part.

Besides these, let us take a look into some typical examples of how conditioned stimulus works in everyday situations.

1. Virus + Favourite Pizza

Jane is coming down with a virus and is currently not aware of it yet. Jane is outside ordering takeaway food. It is a delicious pizza that she eats regularly.

Upon arriving home, Jane eats the pizza and shortly after gets a bad feeling of nausea.

Naturally, Jane will instantly link nausea and the urge to vomit with the pizza, not the underlying virus. Next time, Jane will avoid her favourite pizza remembering how nauseated it made her feel.

In this instance, pizza is the conditioned stimulus for Jane, since it leads to a belief that she will get sick every other time when she orders this particular pizza.

2. Taxi driver + The Whistling Sound

Mike has been a taxi driver for 13 years already.

Whenever he is available for the ride, potential passengers stop him by raising a hand and whistling.

One day, Mike hears a whistling sound and stops. As it happens, nobody needed the taxi, it is just local kids playing in the courtyard.

As it turns out, whistling became the environmental, i.e. conditioned stimulus for Mike since he linked it with a person calling for a taxi.

3. School + Bullying

Tom is a chubby but sweet little boy who is 11 years old and likes school very much.

However, other kids keep either teasing or openly bullying him, saying how obese he is and attributing to him numerous negative nicknames.

Eventually, Tom stops feeling happy about going to school and he starts looking for excuses to stay at home.

When left with no other choice, the parents decide to transfer him to another school, but his reluctance still prevails.

The bullying is the conditioned stimulus for Mike, since he linked it with school kids and school in general and is afraid to interact with other children.

4. Riding a Bike + Falling Down

Michelle rides her bike to work every morning. She is very skilled and usually very careful when riding a bike. However, one morning she falls down.

The next morning, she additionally slows down on the place where she fell as a means of being extra careful.

When she fell down, Michelle associated the path, i.e. the precise location, with the fall so this place becomes the conditioned stimulus for her.


Having introduced a few typical examples of conditioned stimulus in real life, we can move on and say how classical conditioning can be used to reverse some of the negative feelings in humans. Besides these, classical conditioning has a wide scope of applicability.

For example, if a child does not like a particular subject at school, the teacher can apply classical conditioning, i.e. conditioned stimulus, to help her overcome her aversion towards the subject.

The teacher can achieve this by presenting the teaching material in a funny way or link the topic with the student’s other interest.

In such a way, the student will begin to relieve herself of the feeling of aversion and will gradually stop disliking the given subject.

Next, conditioned stimulus can be used in treating and overcoming various phobias in patients suffering from these.

For example, the therapist can gradually expose the patient to the object that the phobia is directed to, combining it with relaxation techniques.

In such a way, the patient will start pairing the object he was initially afraid of with feeling relaxed. As time progresses, the phobia will gradually subside.

Besides humans, the conditioned stimulus might also be effective in training animals to certain behaviours you want to suppress or promote.

For example, a farmer may protect his crops from domestic animals by giving them crops mixed with some additive causing indigestion.

In that case, the animals will try the food (crops) and see that there is something wrong with it.

In that case the conditioned stimulus helps to suppress their natural urge to feed themselves with the crops farmer needs for his own purpose.


The human brain is a mystery which remains unravelled after decades of exploration and study.

Centuries have passed and humankind made enormous scientific progress, but when it comes to brains there is so much more to be investigated.

Multiple and extensive research will still have to be made in the years, even decades, to come before we are fully able to understand how this little mechanism in our head works.

Still, one thing is certain. Our brain is always busy working, being active and leading multiple processes relevant for our normal functioning, such as walking, moving our hands, speaking, and perceiving the world around us.

Moreover, it turns out our brain can be tricked into believing something by simply being exposed to certain stimuli.

As this article briefly depicted, our brain can pair up two completely unrelated actions and produce a result which was supposed to be achieved by only one of those actions.

If you keep repeating the unplanned circumstance, that is, the stimulus, with the planned one the result you wanted to achieve will be inevitable.

The above is the main postulate of classical conditioning model accidentally discovered by Russian psychologist Ivan Pavlov.

Since his time, the theory has been developed further and applied in many situations, and it has even been disputed as deterministic and favouring nurture over nature.

If we leave out the experimental factor, one must inevitably say that classical conditioning has found its place in behavioural psychology and that conditioned stimulus is found its place in many therapy methods.

If applied appropriately, it can help patients with phobias, addicts of various kinds or simply people with negative feelings.

How the Conditioned Stimulus Works in Classical Conditioning

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