Classical conditioning, also known as Pavlovian conditioning or response conditioning, is a learning process characterised by the association between stimuli and responses. It was first proposed by the Russian physiologist and psychologist Ivan Petrovich Pavlov.

His father was a clergyman, and under his father’s influence, Pavlov initially studied theology but later switched to the natural sciences. In 1879, he was awarded a doctorate and received a gold medal.

In his early years, Pavlov led a highly regimented life and work routine: he would have lunch punctually at 12 noon every day, go to bed at the same time each evening, feed his dog at the same time, and travel to Estonia at the same time every year. Later, following the death of his son Victor, he suffered from severe insomnia.

I am sure everyone is already very familiar with Pavlov’s dog experiments. By exposing dogs to stimuli such as a red light or a bell before feeding, over time the dogs would form an associative mechanism in response to these stimuli.

Previously, the dogs would only secrete saliva whilst eating, but once the associative mechanism was established, they would begin to secrete saliva upon the appearance of the red light or the ringing of the bell. Based on this phenomenon, Pavlov termed this associative learning process a ‘conditioned reflex’.

Classical conditioning is further divided into unconditioned and conditioned responses.

An unconditioned response, also known as an unconditioned reflex, is innate. It is a reflexive reaction triggered by an external stimulus that is transmitted via the reflex arc to the nervous system. In this case, no acquired learning is required; it involves the body’s lower-level neural centres, such as the brainstem and spinal cord, and constitutes a survival instinct. 

There are many examples of unconditioned reflexes in everyday life, such as the knee-jerk reflex, the blink reflex and the withdrawal reflex. In Pavlov’s dog experiment, the dogs’ salivation upon seeing food is an example of an unconditioned reflex.

A conditioned reflex (conditioned response), on the other hand, requires learning and involves the higher nervous centres, namely the cerebral cortex; the unconditioned reflex forms the basis for the conditioned reflex. Through the repeated pairing of a conditioned stimulus with an unconditioned response, a reinforced conditioned response can be established. 

Both humans and animals associate the conditioned stimulus with the unconditioned response, forming a connection that manifests as the unconditioned response.

In Pavlov’s dog experiment, this involved pairing the ringing of a bell with the presentation of food; the dogs gradually developed an unconditioned response—salivation—to the sound of the bell. This process is known as a conditioned reflex.

In this experiment, the formation and extinction of conditioned responses are divided into four stages:

The first stage is based on an unconditioned response, whereby the dog salivates upon seeing food;

The second stage involves introducing a neutral stimulus into the unconditioned response described above, such that ‘food + bell’ = salivation;

In the third stage, the dog develops an unconditioned response to the neutral stimulus introduced in the previous stage, salivating upon hearing the bell even when no food is present.

In the fourth stage, once the neutral stimulus is no longer strongly associated with the food, the dog will no longer salivate upon hearing the bell; this phenomenon is known as the extinction of the conditioned reflex.

The famous Little Albert experiment utilised the principles of conditioned reflexes. This experiment was conducted in 1920 at Johns Hopkins University in the United States by the American psychologist John B. Watson, together with his assistant Rosalie Rayner.

Watson’s father was a short-tempered smallholder who eloped with another woman when Watson was 13; his mother then moved with the young Watson to the city. Coming from a rural background, Watson was frequently mocked and ridiculed by his schoolmates, which led the teenage Watson to commit many foolish acts; he was arrested twice, on one occasion for firing a gun in the city. 

Yet deep down, Watson yearned for knowledge. Thanks to the efforts of his mother and himself, he was able to enrol at the local Forman University, where he went on to obtain a master’s degree five years later, at the age of 21.

He subsequently went to the University of Chicago to further his studies alongside his former philosophy professor, Gordon Moore. Initially, he studied philosophy, but soon found psychology fascinating and switched to studying psychology and physiology.

In 1913, he published an article entitled ‘Psychology from the Behaviourist’s Point of View’—also known as the ‘Behaviourist Manifesto’—in which he introduced the concept of ‘behaviourism’ and asserted that psychology is a wholly objective, experimental natural science. He emphasised a focus on human behaviour rather than mental states.

Influenced by Pavlov’s experiments with dogs, he began to focus on the behaviour of children, which led to the ‘Little Albert’ experiment. Together with his assistant, Reiner, he found Little Albert in a hospital and persuaded his mother to allow him to take part in a psychological experiment; Little Albert was nine months old at the time. 

Before the experiment began, they conducted a series of basic emotional tests on Little Albert to observe his reactions to white mice, monkeys, rabbits, dogs, cotton wool, burning newspapers, and masks with and without hair. The results indicated that Little Albert currently exhibited no fear towards any of these objects.

The formal experiment was conducted when Little Albert was 11 months old. They placed a mattress in the centre of the room, had Little Albert sit on it, and placed a small white rat in front of him. Out of curiosity, Little Albert began to fiddle with the rat and reached out to touch it; at this point, he showed no signs of fear whatsoever.

Subsequently, when Albert touched the little white mouse, Watson and his assistant, Rena, who were standing behind Albert, produced a loud noise with a hammer and an iron bar. Upon hearing the noise, little Albert burst into tears and appeared extremely frightened. After repeating this procedure several times, when the little white mouse was placed in front of Albert again—even without the loud noise—he would still cry and try to flee, displaying fear.

Through a series of learning behaviours, little Albert’s brain associated the white rat—a neutral stimulus—with the loud noise—an unconditioned stimulus—triggering a fear response. Once the four stages of conditioned reflex had been completed, the white rat gradually became a conditioned stimulus, meaning that even without the loud noise, it could independently trigger a fear response.

Moreover, this fear extended to other similar objects. Half a month after the first experiment, Albert was brought back to the laboratory and the white mouse was replaced with a small rabbit; upon seeing the rabbit, Albert similarly displayed fear, and other soft, furry objects had a similar effect.

Although this experiment is very well known, it has also been met with considerable scepticism. Firstly, it has been pointed out that little Albert showed signs of dementia and developmental disabilities, and the validity of experimental results involving children with such conditions is open to question. 

Secondly, after the experiment concluded, Watson did not extinguish little Albert’s fear conditioned reflex, which would have had a significant impact on his psychological well-being and contravened academic ethics.

Little Albert tragically passed away at the age of six due to cerebral oedema, so we are unable to ascertain the impact of Watson’s experiment on his subsequent development.