Pavlov found that once he conditioned a dog to salivate in response to a tone, a tone that was slightly higher or lower in pitch would also make the dog salivate. this phenomenon is called:

Stimulus generalization

Explanation:

Stimulus generalizationis is when a subject responds to a stimulus or a group of stimuli similar but not identical to the original situation. For example the dog salivating at a slightly higher or lower pitch not only to the exact tone is a stimulus that is similar but not the original. The animal responds to the similar stimulus in the same way it would to the conditioned stimulus.