ABSTRACT
The primary motivation behind a great deal of research and theorizing in Pavlov ian conditioning has been to provide an account of certain “ failures of contigu ity.” That is, to explain why the same degree of CS-US contiguity does not necessarily produce the same degree of performance to the CS (e.g., Gibbon & Balsam, 1981; Kamin, 1969; Mackintosh, 1975; Pearce & Hall, 1980; Rescorla, 1968; Rescorla & Wagner, 1972; Wagner, 1969, 1981). For example, although repeated pairings of a CS, X, and a US typically result in the development of conditioned responding to X, if X is accompanied by another salient cue (A) on the occasion of those pairings, the degree of conditioned responding elicited by X alone will not be as great (A is said to overshadow X; Kamin, 1969; Pavlov, 1927). Moreover, A’s own relation with the US affects its ability to interfere with conditioning to X. Separate reinforced presentations of A will enhance A’s ability to interfere with conditioning to X (blocking), whereas separate nonrein forced presentations will reduce it (Wagner, 1969). Even in the absence of an explicit interfering cue, the same number of CS-US pairings will not necessarily support the same level of conditioned responding. Factors such as the time be tween CS-US pairings and the rate at which the US occurs in the absence of the CS also seem to have an effect (e.g., Terrace, Gibbon, Farrell, & Baldock, 1975; Rescorla, 1968, 1969).
