Like many great scientific advances, Pavlovian conditioning (aka classical conditioning) was discovered accidentally. Ivan Petrovich Pavlov (1849–1936) was a physiologist, not a psychologist.
During the 1890s, Pavlov researched salivation in dogs in response to being fed. He inserted a small test tube into the cheek of each dog to measure saliva when the dogs were fed (with a powder made from meat).
Pavlov predicted the dogs would salivate in response to the food placed in front of them, but he noticed that his dogs would begin to salivate whenever they heard the footsteps of his assistant who was bringing them the food.
When Pavlov discovered that any object or event which the dogs learned to associate with food (such as the lab assistant) would trigger the same response, he realized that he had made an important scientific discovery.
Accordingly, he devoted the rest of his career to studying this type of learning.
Pavlovian Conditioning
Pavlov (1902) started from the idea that there are some things that a dog does not need to learn. For example, dogs don’t learn to salivate whenever they see food. This reflex is ‘hard-wired’ into the dog.
In behaviorist terms, food is an unconditioned stimulus and salivation is an unconditioned response. (i.e., a stimulus-response connection that required no learning).
Unconditioned Stimulus (Food) > Unconditioned Response (Salivate)
In his experiment, Pavlov used a metronome as his neutral stimulus. By itself, the metronome did not elicit a response from the dogs.
Neutral Stimulus (Metronome) > No Conditioned Response
Next, Pavlov began the conditioning procedure, whereby the clicking metronome was introduced just before he gave food to his dogs. After a number of repeats (trials) of this procedure he presented the metronome on its own.
As you might expect, the sound of the clicking metronome on its own now caused an increase in salivation.
Conditioned Stimulus (Metronome) > Conditioned Response (Salivate)
So the dog had learned an association between the metronome and the food and a new behavior had been learned.
Because this response was learned (or conditioned), it is called a conditioned response (and also known as a Pavlovian response). The neutral stimulus has become a conditioned stimulus.
Pavlov found that for associations to be made, the two stimuli had to be presented close together in time (such as a bell).
He called this the law of temporal contiguity. If the time between the conditioned stimulus (bell) and unconditioned stimulus (food) is too great, then learning will not occur.
Pavlov and his studies of classical conditioning have become famous since his early work between 1890-1930. Classical conditioning is “classical” in that it is the first systematic study of basic laws of learning / conditioning.
Summary
To summarize, classical conditioning (later developed by Watson, 1913) involves learning to associate an unconditioned stimulus that already brings about a particular response (i.e., a reflex) with a new (conditioned) stimulus, so that the new stimulus brings about the same response.
Pavlov developed some rather unfriendly technical terms to describe this process. The unconditioned stimulus (or UCS ) is the object or event that originally produces the reflexive / natural response.
The response to this is called the unconditioned response (or UCR). The neutral stimulus (NS) is a new stimulus that does not produce a response.
Once the neutral stimulus has become associated with the unconditioned stimulus, it becomes a conditioned stimulus (CS). The conditioned response (CR) is the response to the conditioned stimulus.
Experiment Summary
Classical conditioning is learning through association and was first demonstrated by Ivan Pavlov.
Pavlov showed that dogs could be conditioned to salivate at the sound of a bell if that sound was repeatedly presented at the same time that they were given food.
First the dogs were presented with the food, they salivated. The food was the unconditioned stimulus and salivation was an unconditioned (innate) response.
Then Pavlov sounded the bell (neutral stimulus) before giving the food.
After a few pairings the dogs salivated when they heard the bell even when no food was given. The bell had become the conditioned stimulus and salivation had become the conditioned response.
The dogs had learnt to associate the bell with the food and the sound of the bell and salivation was triggered by the sound of the bell.
Pavlov showed that classical conditioning leads to learning by association. Watson and Rayner showed that phobias can be learnt through classical conditioning in the “ little Albert ” experiment.
References
Pavlov, I. P. (1897/1902). The work of the digestive glands. London: Griffin.
Pavlov, I. P. (1928). Lectures on conditioned reflexes. (Translated by W.H. Gantt) London: Allen and Unwin.
Pavlov, I. P. (1927). Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex. Translated and edited by Anrep, GV (Oxford University Press, London, 1927).
Pavlov, I. P. (1955). Selected works. Moscow: Foreign Languages Publishing House.
Watson, J.B. (1913). Psychology as the behaviorist Views It. Psychological Review, 20, 158-177.
