Classical Conditioning

Description of the Strategy

Classical conditioning is a procedure used to study behavioral change. The procedure was developed around 1900 by the Russian physiologist Ivan P. Pavlov in the course of his research on the physiology of digestion. The defining feature of the procedure is that the presentation of an eliciting stimulus is dependent upon the prior occurrence of a relatively “neutral” stimulus. In Pavlov's laboratory, food commonly served as the eliciting stimulus, with salivation as the elicited response, and events such as the sound of a ticking metronome or the sight of a rotating black square served as neutral stimuli. After several pairings of the neutral stimulus with the eliciting stimulus, the neutral stimulus began to evoke salivation prior to the presentation of food and during test trials in which the neutral stimulus was presented alone. That is, the ticking sound itself came to evoke salivation. Pairing the neutral stimulus with the eliciting stimulus had produced a new environment-behavior relation: soundsalivation. The procedure is termed classical conditioning, because it was the first procedure used to systematically investigate the acquisition of environment-behavior relations. The procedure is also known as Pavlovian conditioning, to acknowledge its originator, or as respondent conditioning, to emphasize that the behavior is evoked in response to a specified stimulus instead of being emitted. An emitted response results from the action of unspecified environmental and intraorganismic events, such as when a novel environment engenders exploratory behavior. The acquisition of environment-behavior relations involving emitted responses is studied with a different procedure known as operant or instrumental conditioning.

The various stimuli and responses that appear in the classical procedure are designated by technical terms that originated with Pavlov. The neutral stimulus (e.g., a sound) is known as the conditioned stimulus, to emphasize that its ability to evoke behavior is dependent upon, or conditional upon, its pairing with the eliciting stimulus. The eliciting stimulus (e.g., food) is termed the unconditioned stimulus, to indicate that its ability to evoke the elicited response is independent of the organism's experience with the elicitor in the experiment. The elicited response (e.g., salivation) is known as the unconditioned response. The response that comes to be evoked by the conditioned stimulus after pairing is termed the conditioned response (also salivation in the example), because its occurrence is dependent upon pairing the conditioned stimulus with the unconditioned stimulus. (The correct English translations of Pavlov's original text are condition al and uncondition al, not conditioned and unconditioned, but the latter terms have persisted because of the faulty initial translation.) Few stimuli are truly neutral—have no behavioral effects—and the responses that initially occur to the to-be-conditioned stimulus are also acknowledged and are known as orienting responses. In technical writing, these events are commonly abbreviated CS for conditioned stimulus, US (or UCS) for unconditioned stimulus, UR (or UCR) for unconditioned response, CR for conditioned response, and OR for orienting response.

Many important behavioral phenomena have been discovered using the classical procedure; extinction, discrimination, generalization, spontaneous recovery, and higher-order conditioning are but a few examples. However, the present discussion focuses on the conditions that have been identified with the classical procedure as necessary to produce behavioral change. Beginning with Pavlov, and confirmed in many later studies, a close temporal relation between the CS and the US/UR is essential for learning. As an example, the sound had to immediately precede food/salivation if it was to function as a CS. When the UR has a very short latency (such as an eye-blink elicited by an airpuff), a CS-US/UR interval of less than a second is optimal. When the UR has a longer latency (such as a change in heart rate elicited by electric shock), an interval of a few seconds is optimal. The finding that the CS-US/UR interval is crucial for learning exemplifies the contiguity requirement. Until the 1960s, it was generally believed that contiguity of the CS with the US/UR was sufficient for learning with the classical procedure. However, a number of studies, conducted principally by Robert Rescorla, began to call [Page 186]this idea into question. These studies appeared to show that learning could be produced by classical procedures in which occurrences of the CS and US/UR were simply correlated with one another: For example, acquisition occurred if the US/UR was more likely during extended time periods containing the CS than during equally long periods in which the CS was absent. These findings encouraged a molar conception of learning in which a general relationship between the occurrences of CSs and US/URs was thought to produce behavioral change without specific CS-US/ UR contiguity.

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