How did Ivan Pavlov explain a dog’s salivation in response to a metronome?

Ivan Pavlov explained a dog’s salivation in response to a metronome through the process of classical conditioning, a form of associative learning.12

In his experiments, Pavlov identified two types of stimuli and responses:

• Unconditioned Stimulus (US): Food, which naturally and invariably elicits salivation, known as the unconditioned response (UR).12
• Conditioned Stimulus (CS): The ticking of a metronome, which is initially neutral.12

By repeatedly pairing the sound of the metronome with the delivery of food, the metronome became a signal that predicted the arrival of the meal. Eventually, the dog learned to associate the sound with the food, causing the metronome alone to elicit salivation. This learned reaction is termed a conditioned response (CR), and the entire process is known as a conditioned reflex. If the metronome is presented repeatedly without being followed by food, the response gradually disappears, a process called extinction.12