Ivan Pavlov studied the reflexive flow of saliva in dogs. He used meat powder to trigger the salivation. It was later observed that the salivation occurred even before the food was placed in the dog’s mouth—at the sight of the food dish. The salivation at the sight of the food dish is an example of a(n) .
a. unconditioned response
b. unconditioned stimulus
c. conditioned response
d. conditioned stimulus