What Is Stimulus Generalization?

Stimulus generalization
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In the conditioning process, stimulus generalization is the tendency for the conditioned stimulus to evoke similar responses after the response has been conditioned. For example, if a child has been conditioned to fear a stuffed white rabbit, it will exhibit fear of objects similar to the conditioned stimulus such as a white toy rat.

One famous psychology experiment perfectly illustrated how stimulus generalization works.

In the classic Little Albert experiment, researchers John B. Watson and Rosalie Rayner conditioned a little boy to fear a white rat. The researchers observed that the boy experienced stimulus generalization by showing fear in response to similar stimuli including a dog, a rabbit, a fur coat, a white Santa Claus beard and even Watson's own hair.

Stimulus generalization also explains why the fear of a certain object often affects many similar objects. A person who is afraid of spiders generally won't be afraid of just one type of spider. Instead, this fear will apply to all types and sizes of spiders. The individual might even be afraid of toy spiders and pictures of spiders as well.

This fear may even generalize to other creatures that are similar to spiders such as other bugs and insects. 

Stimulus Generalization in Classical and Operant Conditioning

Stimulus generalization can occur in both classical conditioning and operant conditioning.

Little Albert's fear of white furry objects is a great example of how stimulus generalization works in classical conditioning. While the child had originally been conditioned to fear a white rat, his fear also generalized to similar objects.

In operant conditioning, stimulus generalization explains how we can learn something in one situation and apply it to other similar situations.

For example, imagine that parents punish their son for not cleaning his room. He eventually learns to clean up his messes to avoid punishment. Instead of having to relearn this behavior at school, he applies the same principles he learned at home to his classroom behavior and cleaned up his messes before the teacher could punish him.

Stimulus Generalization and Stimulus Discrimination

However, a subject can be taught to discriminate between similar stimuli and only to respond to a specific stimulus. For example, imagine that a dog has been trained to run to his owner when he hears a whistle. After the dog has been conditioned, he might respond to a variety sounds that are similar to the whistle. Because the trainer wants the dog to respond only to the specific sound of the whistle, the trainer can work with the animal to teach him to discriminate between different sounds. Eventually, the dog will respond only to the whistle and not to other tones.

In another classic experiment conducted in 1921, researcher Shenger-Krestovnika paired the taste of meat (the unconditioned stimulus) with the sight of a circle.

The dogs then learned to salivate (the conditioned response) when they saw the circle. Researchers also observed that the dogs would begin to salivate when presented with an ellipse, which was similar but slightly different that the circle shape. After failing to pair the sight of the ellipse with the taste of meat, the dogs were able to discriminate eventually between the circle and ellipse.

As you can see, stimulus generalization can have an important impact on the response to a stimulus. Sometimes individuals are able to discriminate between similar items, but in other cases similar stimuli tend to evoke the same response.

Sources:

Gray, Jeffrey A. (1979)"Ivan Pavlov. NY: Viking.

Watson, J. B. & Rayner, R. (1920). Conditioned emotional reactions. Journal of Experimental Psychology, 3, 1-14.

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