stimuli are similar, not identical, to the CS produce CR, this is
Stimulus generalization
known as stimulus generalization.
Stimulus generalization occurs when a response that has been learned in response to a specific stimulus also occurs in response to similar stimuli. The degree of similarity between the original stimulus and the similar stimuli determines the likelihood and strength of the response.
For example, if a dog has learned to salivate at the sound of a bell (CS), it may also salivate at the sound of a similar tone such as a doorbell or an alarm clock. The response to the similar stimuli is called the generalization gradient. The gradient indicates the strength of the response to stimuli that are similar to the original stimulus.
Stimulus generalization is an adaptive process that helps animals and humans respond appropriately to a range of stimuli in their environment. However, it can also lead to overgeneralization, where the response occurs to stimuli that are not relevant or even harmful. For example, a child who has learned to fear dark alleys may also become afraid of dimly lit hallways, even if they are safe.
In summary, stimulus generalization occurs when a learned response to a specific stimulus also occurs to similar stimuli. The degree of similarity between the stimuli determines the strength of the response.