What Is Stimulus Discrimination?

Stimulus discrimination in animal training
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Discrimination is a term used in both classical and operant conditioning. It involves the ability to distinguish between one stimulus and similar stimuli. In both cases, it means only responding to certain stimuli but not to those that are similar.

Discrimination in Classical Conditioning

In classical conditioning, discrimination is the ability to differentiate between a conditioned stimulus and other stimuli that have not been paired with an unconditioned stimulus.

For example, if a bell tone were the conditioned stimulus, discrimination would involve being able to tell the difference between the bell sound and other similar sounds.

The classical conditioning works like this:

A previously neutral stimulus is paired with an unconditioned stimulus (UCS). The unconditioned stimulus represents something that naturally and automatically triggers a response. Salivating to the smell of food, for example, is an unconditioned response. After an association has been formed, the previously neutral stimulus, now known as the conditioned stimulus (CS) can evoke the same response, now known as the conditioned response, even when the UCS is not present.

In Pavlov's classic experiments, the sound of a tone was repeatedly paired with the presentation of food, which naturally and automatically led to a salivary response. Eventually, the dogs would salivate in response to the sound of the tone alone.

Now, imagine that Pavlov introduced a different sound to the experiment. Instead of presenting the sound of the tone, let's imagine that he sounded a trumpet. What would happen?

If the dogs did not drool in response to the trumpet noise, it means that they are able to discriminate between the sound of the tone and the similar stimulus.

Not just any noise will produce the conditioned response. Because of stimulus discrimination, only a very particular sound will lead to the conditioned response.

In one well-known experiment on classical conditioning, researchers paired the taste of meat (UCS) with the sight of a circle (CS), and dogs learned to salivate in response to the presentation of a circle. The researchers also found, however, that the dogs would also salivate when they saw an ellipse. Over time, as the dogs experienced more and more trials where they did not experience the taste of meat upon seeing the ellipse, they eventually became able to discriminate between the two similar stimuli. They would salivate in response to the circle, but not when they saw the ellipse.

Discrimination in Operant Conditioning

In operant conditioning, discrimination refers to responding only to the discriminative stimulus and not to similar stimuli.

For example, imagine that you have trained your dog to jump in the air whenever you say the command "Jump!" In this instance, discrimination refers to your dog's ability to distinguish between the command for jumping and similar commands such as sit, stay, or speak.

Stimulus Discrimination vs. Stimulus Generalization

This stimulus discrimination can be contrasted with a similar phenomenon known as stimulus generalization.

In classical conditioning, for example, stimulus generalization would involve being unable to distinguish between the conditioned stimulus and other similar stimuli. In the famous Little Albert experiment, a young boy was conditioned to fear a white rat, but he displayed the fear response upon the presentation of similar white, furry objects.


Shenger-Krestovnikova, N. R. (1921). Contributions to the Physiology of Differentiation of Visual Stimuli, and Determination of Limit of Differentiation by the Visual Analyzer of the Dog. Bulletin of Institute of Lesgaft, iii.

Watson, J. B., & Rayner, R. (1920). Conditioned Emotional Reactions. Journal of Experimental Psychology, 3, 1-14. http://psychclassics.yorku.ca/Watson/emotion.htm.

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