Conditioned lick suppression by water-deprived rats was used to elaborate on recent evidence that the attenuated conditioned response elicited by an overshadowed stimulus may be enhanced by extinction ofthe overshadowing stimulus with which it had been trained in simultaneous compound. Using a modified serial stimulus arrangement in which a light coexisted with the last half of a tone that terminated with footshock, it was found in Experiment 1 that the tone overshadowed the light. Extinction of the tone-shock association resulted in a virtually complete recovery of the response to the overshadowed light. Using this serial overshadowing procedure, the possibility that the strength of a conditioned response to an element trained in compound covaries as a function of the strength of the response to the other element was tested in Experiment 2. Following overshadowing training similar to that of Experiment 1, independent reinforcement of the overshadowed light, that is, associative inflation, was found to have no deleterious effect on the response to the overshadowing tone. This suggests that the effects of postconditioning extinction and inflation of one element do not have symmetrical effects upon responding to the other element. The results of Experiment 2 were replicated in Experiment 3 using a simultaneous compound stimulus as opposed to the serial compound of the previous studies. These results are discussed in terms of various associative and cognitive models of learning and performance.Recent reports by Kaufman and Bolles (1981) and Matzel, Schachtman, and Miller (1985) have indicated that the attenuated response evoked by a weak stimulus (X) following reinforcement in compound with a more salient stimulus (A) can be enhanced by postconditioning extinction (i.e., nonreinforced exposure) of A. These results challenge the traditional view that "overshadowing" deficits represent an acquisition failure with respect to the less salient cue (Kamin, 1969a;Mackintosh, 1975;Pavlov, 1927;Rescorla & Wagner, 1972). Kamin, for instance, suggested that when the more salient A stimulus is reinforced in compound with X, A acquires associative strength at a more rapid rate, quickly becoming a reliable predictor of the unconditioned stimulus (US). As the US is no longer "surprising," the less salient X cue, which is still at a subasymptotic associative level, acquires no additional associative strength. Similarly, Rescorla and Wagner (1972) proposed that the associative strength that a given US presentation can support is limited, and the more salient cue in a reinforced compound accrues the available strength at the expense of the less salient cue. These views of overshadowing assume that increments in associative strength are determined by the subject's expectation of the particular US paired with the compound stimulus. In contrast, both Mackintosh (1975) and Pearce Support for this research was provided by NSF Grant 86-00755. We are grateful to Ronald Sigmundi for his helpful comments on an early draft of this report. Add...