Why did the metronome become a conditioned stimulus in Ivan Pavlov’s experiment?

In the experiments conducted by the Russian physiologist Ivan Pavlov, the metronome became a conditioned stimulus because it was consistently presented as a signal immediately preceding the delivery of food.12

Initially, the food served as an unconditioned stimulus that naturally elicited salivation, known as the unconditioned response. By repeatedly pairing the ticking of the metronome with the subsequent arrival of food, Pavlov established a temporal relationship between the two events. Through this process of classical conditioning, the dog learned to associate the sound of the metronome with the food.12

Consequently, the metronome acquired the ability to elicit salivation on its own, transforming it into a conditioned stimulus. The resulting salivation in response to the metronome alone is termed a conditioned response.12