CHARACTERISTICS OF THE LITHIUM-MEDIATED PROXIMAL UNCONDITIONED STIMULUS PREEXPOSURE EFFECT IN FLAVOR-AVERSION CONDITIONING

Taste-aversion learning in rats is disrupted if the subjects are exposed to the unconditioned stimulus (US) shortly before the conditioning trial but not if this single US preexposure treatment occurs 1 day or more before conditioning. Several characteristics of this proximal US-preexposure phenomenon were explored. Experiment 1 showed that the time course of the interference with conditioning is directly related to the preexposure drug dose. Experiment 2 demonstrated that the interference effect is evident even if the test for aversion learning is conducted following a drug injection, thereby minimizing stimulus generalization decrement for the preexposed subjects. Finally, Experiment 3 showed that disruption of the contingent relationship between tastes and drug effects is probably not responsible for the proximal US-preexposure phenomenon because the interference with conditioning occurs regardless of whether or not the preexposure drug treatment is paired with a novel flavor. These findings, together with previous research, demonstrate the remarkably robust character of the proximal US-preexposure phenomenon. © 1979 Psychonomic Society, Inc.