Pavlovs Dogs Get Conditioned

This video, part of the Introductory Psychology Video Tool Kit (BBC Motion Gallery), is a recreation of Pavlovs laboratory experiments on the salivation reflex.

It shows the discovery of the conditioned reflex in dogs and summarizes Pavlov’s paradigm to study dogs’ salivation reflex. Pavlov uses a variety of stimuli in his study of animal learning. Why did Pavlov vary the stimuli used to elicit the conditioned reflex in dogs?