What role did food play in Ivan Pavlov’s conditioning experiments?

In Ivan Pavlov’s experiments, food served as the unconditional stimulus because it invariably elicited an unconditional response—in this case, the salivation of a hungry dog.1

Initially, Pavlov observed that dogs salivated not only when food was placed in their mouths but also in response to the sight or smell of food and the presence of the technician who provided it. He termed these "psychic secretions" and recognized them as a tool for studying conditioning.1

By pairing an arbitrary stimulus, such as the sound of a metronome, with the delivery of food, Pavlov demonstrated that the animal could learn to associate the two. The food acted as a reinforcer for the conditional reflex; however, if the food was no longer presented following the conditional stimulus, the conditioned response would gradually disappear, a process known as extinction.1