LEARNING AND MOTIVATION l&522-537 (1980) Interference with Ingestional Aversion Learning Produced by Preexposure to the Unconditioned Stimulus: Associative and Nonassociative Aspects MICHAEL DOMJAN The Universiry of Texas at Austin AND MICHAEL R. BEST Southern Methodist University Preconditioning exposure to a lithium chloride unconditioned stimulus (US) interferes with the subsequent conditioning of a taste aversion. Multiple US preexposures produce a long-lasting or durable interference with aversion leam- ing, whereas a single US exposure produces a transient interference effect. The present experiments demonstrate that the durable US preexposure effect is sub- stantially reduced if the method of drug treatment (infusion versus injection of the drug into the peritoneal cavity) or the spatial cues present during drug treatment (home cage versus a distinctive environment) are changed between the preexpo- sure and taste conditioning phases of the experiment. In contrast, these manipula- tions do not attenuate the proximal/transient US preexposure effect. These findings indicate that different mechanisms are responsible for the two US preex- posure effects. The results are consistent with previous suggestions that the durable effects of lithium preexposure are due to associative interference pro- duced by the exteroceptive stimuli that accompany drug administrations and indicate that the proximal/transient US preexposure effect is mediated by nonas- sociative mechanisms. Rats injected with a drug such as lithium chloride after exposure to a novel flavored solution learn an aversion to the flavor as a result. Such taste-aversion learning occurs readily in one trial and is one of the most We wish to thank Van Miller and Mike Hanlon for their techhical assistance with Experiment I, and Dr. Claude Desjardins for his advice on the cannula technique used in Experiment I. We also thank John Batson for his aid in the preparation of all figures in this report. The research was supported by Grants MH 30788-02 (from the Public Health Service) and BNS 77-01552 (from the National Science Foundation). Requests for reprints may be addressed to Michael Domjan, Department of Psychology, University of Texas, Austin, TX 78712, or Michael R. Best, Department of Psychology, Southern Methodist University, Dallas, TX 75275. 522 0023-%90/80/040522-l6$02.00/0 Copyright @ 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.