classical conditioning - discovered by Ivan Pavlov

Classical conditioning (also known as Pavlovian or respondent conditioning) is a learning process in which an innate response to a potent stimulus comes to be elicited in response to a previously neutral stimulus; this is achieved by repeated pairings of the neutral stimulus with the potent stimulus. The basic facts about classical conditioning were discovered by Ivan Pavlov through his famous experiments with dogs. Together with operant conditioning, classical conditioning became the foundation of Behaviorism, a school of psychology which was dominant in the mid-20th century and is still an important influence on the practice of psychological therapy and the study of animal behaviour (ethology). Classical conditioning is now the best understood of the basic learning processes, and its neural substrates are beginning to be understood.Classical conditioning occurs when a conditioned stimulus is paired with an unconditioned stimulus. Usually, the conditioned stimulus (CS) is a neutral stimulus (e.g., the sound of a tuning fork), the unconditioned stimulus (US) is biologically potent (e.g., the taste of food) and the unconditioned response (UR) to the unconditioned stimulus is an unlearned reflex response (e.g., salivation). After pairing is repeated (some learning may occur already after only one pairing), the organism exhibits a conditioned response (CR) to the conditioned stimulus when the conditioned stimulus is presented alone. The conditioned response is usually similar to the unconditioned response (see below), but unlike the unconditioned response, it must be acquired through experience and is relatively impermanent.

In classical conditioning, the conditioned stimulus is not simply connected to the unconditioned response; the conditioned response usually differs in some way from the unconditioned response, sometimes significantly. For this and other reasons, learning theorists commonly suggest that the conditioned stimulus comes to signal or predict the unconditioned stimulus, and go on to analyze the consequences of this signal. Robert A. Rescorla provided a clear summary of this change in thinking, and its implications, in his 1988 article "Pavlovian conditioning: It's not what you think it is."Despite its widespread acceptance, Rescorla's thesis may not be defensible.

Classical conditioning differs from operant or instrumental conditioning: in classical conditioning, behavioral responses are elicited by antecedent stimuli, whereas in operant conditioning behaviors are strengthened or weakened by their consequences (i.e., reward or punishment)