Pavlov noticed that dogs began salivating at the mere sight of the person who regularly brought food to them.For the dogs,the sight of this person was a(n)

A) spontaneous recovery.
B) unconditional stimulus.
C) operant stimulus.
D) conditioned stimulus.

Conditioned Stimulus

An initially indifferent stimulus that, following its connection with an unconditioned stimulus, eventually induces a conditioned response.

Unconditional Stimulus

Regarding classical conditioning, a stimulus spontaneously and automatically produces a response, requiring no earlier learning.

Operant Stimulus

A stimulus that follows a behavior and increases or decreases the likelihood of that behavior occurring again; used in operant conditioning.