In classical conditioning, individuals learn an association between the CS and UCS. For example, A dog who is treated cruelly by its male owner learns to be afraid of that man. The CS, in this example, is the sight, sound, etc. of the man, the UCS is the cruel treatment, the UCR is the distress elicited by the cruel treatment, and the CR is fear of the man. Sometimes, the dog not only becomes afraid of the man who treats it cruelly but it also may become afraid of all men. This shows that the dog has learned something about the characteristics of men, in general — such as their smell, body shape, walking gait, height, deepness of voice, etc. — and has learned to be afraid of any human with these characteristics. The dog has generalized its fear of its male owner to other men. The tendency for stimuli similar to a CS to also elicit a CR is referred to as stimulus generalization. It occurs in virtually all cases of classical conditioning since there always are other stimuli that share similarities with the CS.

Let's look at an example of stimulus generalization from a classic experiment on classical conditioning. Shenger-Krestovnika (1921) demonstrated that dogs that experienced the taste of meat (UCS) whenever they saw a circle (CS) learned to salivate to the circle (CR) just as they salivated reflexively (UCR) to the taste of meat (see Figure 1).

Figure 1. Design of the classical-conditioning study of Shenger-Krestovnika (1921)

Shenger-Krestovnika then found that dogs also would salivate to the sight of an ellipse. Thus, for these dogs, the CR of salivation to the sight of a circle showed stimulus generalization to the ellipse (see Figure 2).

Figure 2. Stimulus generalization from a circle to an ellipse

Stimulus Generalization and Phobias

In the case of Little Albert, the baby who was classically conditioned to fear the sight of a white rat after the rat had been paired with an unexpected loud noise, Watson and Rayner (1920) reported that Albert showed a "transfer" of his learned anxiety to a rabbit, a dog, a seal-fur coat, a Santa Claus mask, and perhaps even Watson's hair (although his reactions to these objects were not always consistent, and the study did not include adequate controls for extraneous variables). The classical conditioning theory of phobic disorder states that the learned fear to a CS generalizes (transfers) to other stimuli, with the greatest amount of transfer occurring to stimuli that are most similar to the CS.

What is Stimulus Discrimination?

As described above, Shenger-Krestovnika (1921) found that dogs showed stimulus generalization to the sight of an ellipse when they had been classically conditioned to salivate to the sight of a circle. In the next part of her study, Shenger-Krestovnika continued to pair the circle with meat but never paired the ellipse with meat. She found that, over time, the dogs stopped salivating to the ellipse but continued to salivate to the circle. That is, the dogs were able to discriminate between the ellipse and the circle, and learned that they received meat only after seeing the circle (see Figure 3).

Figure 3. Stimulus discrimination between a circle and an ellipse

The tendency for stimuli similar to a CS to stop eliciting a CR when they are not followed by a UCS is referred to as stimulus discrimination. In other words, with the stimulus-discrimination procedure (illustrated in the work of Shenger-Krestovnika, 1921), the CR extinguishes to the stimulus that is similar to the CS. You may have learned, for example, to respond with anxiety (CR) to a particular tone of voice (CS) used by your parent when that tone, in the past, had repeatedly been followed by an outburst of anger (UCS). On the other hand, your parent may have used a slightly different tone of voice when expressing mock anger. In this case, you probably learned to discriminate between the two and to not become anxious when hearing the tone associated with mock anger.

Stimulus Discrimination and Phobias

The classical conditioning theory of phobic disorder states that individuals learn to discriminate between a CS that is followed reliably by a fear-inducing UCS and stimuli that, although similar, are rarely or never followed by the UCS. For example, in the case of the dog that is fearful of all men because it has been treated cruelly by a particular man, it probably will learn to feel fear only to the man who abused it if most other men the dog meets treat it kindly.

Study Questions for Section 5-11

1. How would you define stimulus generalization in your own words?
2. How did the research of Shenger-Krestovnika (1921) illustrate stimulus generalization?
3. What is an example of stimulus generalization from your everyday life?
4. How is stimulus generalization important for the development of phobias?
5. How might stimulus generalization be an adaptive characteristic? (NOTE: I did not talk about this above, so you'll need to give your answer some thought.)
6. How would you define stimulus discrimination in your own words?
7. How did the research of Shenger-Krestovnika (1921) illustrate stimulus discrimination?
8. What is an example of stimulus discrimination that you have experienced?
9. How is stimulus discrimination important for the development of phobias?
10. How might stimulus discrimination be an adaptive characteristic? (NOTE: I did not talk about this above, so you'll need to give your answer some thought.)

Go to Quiz 5-11 questions

Go to Readings Section 5-12