In Ivan Pavlov’s conditioning experiments with dogs, salivation became associated with the sound of a bell.
Pavlov originally studied digestion and measured dogs’ salivary responses to food. He noticed that the animals could begin salivating before food arrived, responding to signals such as an experimenter’s footsteps. This observation led him to investigate learned associations systematically.
In classical-conditioning trials, a neutral stimulus such as a tone was repeatedly paired with food. After enough pairings, the tone alone could produce salivation. The food was the unconditioned stimulus, the food-related salivation was an unconditioned response, and the learned response to the tone became a conditioned response.
Popular accounts often say Pavlov always used a bell, but his published work used several signals, including metronomes and tones. The central finding was not the particular sound; it was that a previously neutral cue could acquire the power to trigger a physiological response through repeated pairing.