Dylan has a new girlfriend whom he really likes. He programs his cell phone so that every time his girlfriend calls, his phone plays the new Justin Timberlake single. After he has had his phone programmed this way for a little while, he notices that he feels happy whenever he hears the Justin Timberlake song. What is the best term for the role of the Justin Timberlake song?

A) Cognitive inference
B) Behavioral reward
C) Generalization
D) Conditioned stimulus

The Justin Timberlake song has become a conditioned stimulus because Dylan has learned to associate it with the positive experience of receiving a call from his girlfriend, leading to feelings of happiness. This is a classic example of classical conditioning, where a neutral stimulus (the song) becomes associated with an unconditioned stimulus (the girlfriend's call) that naturally elicits an unconditioned response (happiness). After the association is learned, the neutral stimulus alone can elicit a conditioned response (also happiness).