Multiple remote-US preexposures and the blocking effect produced by a proximal-US

Weanling, young-adult, and old-age Wistar albino rats were used to determin e whether number of unconditioned stimulus (US) presentations, given 24 h o r more (remote preexposure) prior to conditioning, alters the blocking effe ct of a single-US preexposure given 2 h before proximal) taste aversion con ditioning. As the number of remote-US preexposures increased from 0 to 6, t he ability of the proximal-US preexposure to block conditioning initially i ncreased then decreased for all age groups. Of the models put forth to expl ain US preexposure effects on conditioned taste aversion (CTA), only Wagner 's information processing model adequately explained the reduction of the b locking effect of the proximal-US preexposure produced as a result of incre asing remote-US preexposures. (C) 2000 Elsevier Science Inc. All rights res erved.