Classical conditioning was first observed by Ivan Pavlov (1927), who at the time was studying digestion in dogs. Pavlov noticed that the dogs were beginning to salivate before they were given their food. He suspected that they were associating things like the footsteps of the approaching researcher with being fed. To find out if this was the case he conducted the following experiment using the now standard classical conditioning procedure (scroll down for video of Pavlov's study):

First Pavlov established that meat powder causes the dog to salivate

Then Pavlov established that a tone did not cause the dog to salivate

Note that the dog is salivating in response to the food at this time.




After several pairings of the tone and food, Pavlov found that the dog would salivate to the tone when it was presented alone.

Video of Pavlov's Classical Conditioning Experiments

Unconditioned Stimulus

The stimulus that causes the reflex response before conditioning. It is called the Unconditioned Stimulus because it has not been conditioned; It is the stimulus that naturally produces the response.

Unconditioned response

The innate (reflexive) response to a stimulus that has not been conditioned.

Neutral stimulus

A stimulus which does not produce the unconditioned response.

Conditioned stimulus

The stimulus which, after repeated pairings with the unconditioned stimulus, produces the response.

Conditioned response

The reflexive response that occurs after exposure to the conditioned stimulus.

Video clip demonstrating classical conditioning in humans

The following are some phenomena that have been uncovered in research into classical conditioning.

extinction

The more often the Conditioned Stimulus is presented alone the weaker the Conditioned Response becomes, until the Conditioned Stimulus no longer elicits the Conditioned Response.

Stimulus Generalisation

Generalisation occurs when the Conditioned Response happens when the animal is presented with a similar stimulus to the Conditioned Stimulus. For example, in Watson and Rayner's (1920) "Case of Little Albert" Albert's fear response to a white rat generalised to a rabbit, a sealskin coat and a Santa Claus mask.

Spontaneous Recovery

If, after extinction has taken place, the animal is taken away from the lab for a short period of time and then returned the Conditioned Stimulus will immediately elicit the Conditioned Response without further pairings of the Conditioned Stimulus and Unconditioned Stimulus.

Stimulus Discrimination

Usually, a conditioned response generalises to similar stimuli, for example a dog conditioned to salivate to a C# tone will also salivate to a C and a D tone; however, if the C and D are repeatedly presented without the food stimulus and the C# presented with the food stimulus, the dog will learn to salivate only to the C# tone. Pavlov’s (1927) famous study “Discrimination between circle and ellipse in dogs” found that dogs were able to make finer and finer discriminations between a circle and an ellipse, however, when the ellipse became indistinguishable from the circle, the dogs behaviour changed:

“The hitherto quiet dog began to squeal in its stand, kept wriggling about, tore off with its teeth the apparatus for mechanical stimulation of the skin, and bit through the tubes connecting the animal's room with the observer, a behaviour which never happened before. On being taken into the experimental room the dog now barked violently, which was also contrary to its usual custom; in short it presented all the symptoms of a condition of acute neurosis.” (Pavlov, 1927)

Some examples of classical conditioning

Fear

Classical Conditioning can produce a fear reaction in rats. When rats are exposed to flashing light paired with brief electric shock a fear response develops after only a few pairings. Sometimes after only a single pairing (Le Doux, 1997)

Eye blink

Classical conditioning can be used on humans, one example is the eye blink response. A sound is paired with a puff of air being blown into a person’s eye, after several pairings the person will blink to the sound alone.