classical conditioning

Meaning: Classical (Pavlovian) conditioning is associative learning in which a neutral stimulus becomes linked to a stimulus that already triggers a reflex. The unconditioned stimulus (US) produces the unconditioned response (UR) without learning. After repeated pairings (acquisition), the former neutral stimulus is a conditioned stimulus (CS) that produces a conditioned response (CR). In Pavlov's dogs, food is the US, salivation to food is the UR, the bell is the CS, and salivation to the bell is the CR.

On the MCAT: Passages describe a scenario, such as nausea after a food, fear of a dentist's office, or Little Albert, and ask you to label the US, UR, CS and CR. Other questions ask what happens when the CS is presented repeatedly without the US (extinction), when the CR returns after a rest (spontaneous recovery), or when similar stimuli also trigger the CR (generalization).

Common confusion: Students mix it up with operant conditioning. In classical conditioning the response is reflexive and is elicited by a stimulus; in operant conditioning a voluntary behavior changes because of its consequences (reinforcement or punishment). Also, the UR and CR are the same kind of response, but the UR follows the US and the CR follows the CS.