What is a conditioned stimulus (CS) in classical conditioning?

In classical conditioning, a conditioned stimulus (CS) is defined as a previously neutral stimulus that, after being associated with an unconditioned stimulus (US) that naturally triggers a response, eventually begins to evoke a conditioned response (CR) on its own. This process takes place through repeated pairings of the CS and the US, allowing the organism to learn the association between the two.

For example, in Pavlov's experiments, the sound of a bell (which was initially irrelevant) became a CS when it was consistently paired with the presentation of food (the US) that naturally elicited salivation (the unconditioned response). After multiple pairings, the bell alone could provoke salivation, demonstrating that the bell had been transformed into a conditioned stimulus through the learning process.

Understanding this concept is crucial in differentiating between the roles of stimuli in classical conditioning and recognizing how learned associations can develop over time.