In Pavlov’s research, classical conditioning occurred when the dogs learned the metronome predicted the arrival of food. This process was based on the animals’ instinctive response to the stimulus.

Unconditioned

Explanation:

This process was based on the animals’ instinctive response to the unconditioned stimulus.

In Pavlov's research, classical conditioning occurred in part because the unconditioned stimuli (food) elicited unconditioned response (salivation).

Unconditioned

Explanation: When responses in an organism occur without predetermination, such responses are unconditioned. Stimulus or events which sparks natural responses are unconditioned stimulus because the response which occurred as a result of that event was not pre-planned. Once the metronome predicted arrival of food, an unlearned response or feeling occurs in the dog's system. This is called an unconditioned stimulus.