Classical conditioning is a basic behavioral process in which stimuli come to evoke responses: When an object or event (such as food) that already evokes a behavior (such as salivation) is associated with one that does not (such as a bell), the latter may evoke a reaction similar to that of the first object or event. When the stimuli are no longer associated, the conditioning weakens (called extinction); when stimuli resemble the conditioned stimulus, they evoke similar reactions (called generalization). First systematically studied by Ivan P. Pavlov (1849-1936), classical conditioning became a model for all behavioral development. B. F. Skinner's (1904-1990) research, for a while, on the conditioning of voluntary (operant) behavior through reinforcement restricted its scope. Classical conditioning occurs only in the involuntary (respondent) behavior of reflexes, glands, and internal organs (e.g., orienting reactions, intestinal functions, insulin secretion, heart rate), especially as they participate in emotional behavior (e.g., anxiety, elation). Today, classical conditioning and extinction are widely used in the treatment of emotional disorders (e.g., phobias) and the side-effects of medical treatments (e.g., nausea caused by chemotherapy).
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Edward K. Morris