Avoidance, Anxiety, and Aversion in the Clinical Setting: The Role of Classical Conditioning
In the classical conditioning procedure, so widely used in the learning laboratory, a neutral cue, otherwise known as a conditioned stimulus (CS), is paired with the occurrence of a motivationally signi®cant event, known as an unconditioned stimulus (US). After a number of CS±US pairings, presentation of the CS alone is capable of producing a conditioned response (CR) that is often similar to that evoked by the US alone. Since the introduction of this experimental arrangement, reported by Pavlov (1927/ 1960), decades of experimental work have demonstrated that this form of learning can operate with a wide range of CSs (visual, auditory, gustatory, and so on) and with a range of USs (such as food, nausea, and electric shock). At a theoretical level, the favoured explanation of the classical conditioning phenomenon has been in terms of a process of association formation, by which the co-occurrence of a pair of events establishes a link between them (or rather, between their central representations). This link allows the presentation of one event (the CS) to evoke some aspects of the behaviour appropriate to the other event (the US). The simplicity of the procedure has ensured its popularity as a laboratory test-bed on which hypotheses about the principles governing associative learning can be examined. The principles established by such work (in particular those describing processes that determine the readiness with which associations can be formed) turn out to have direct relevance to the practical issues that form the bulk of this chapter.