Unified understanding of retarding and facilitating effect of stimulus preexposure

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Using conditioned taste-aversion procedure and rats as the subjects, conditions under which preexposure to conditioned stimulus (CS) facilitates but not retards subsequent acquisition of conditioned aversion were explored. When tap water was used as the CS with animals maintained by salt water through the experiment, preexposure to CS in a context other than experimental one resulted in facilitation of the acquisition of aversion. The same effect was also obtained when salt water rather than CS (tap water) was preexposed in a different context. Simple preexposure to that context without presenting fluid had no effect.The effect of familiarity of a taste CS on the acquisition of context-dependent aversion was also studied. The results of the experiments suggested that only when subjects were given in their home cages a fluid that was identical to the CS through the experiment, conditioning context was established as the occasion setter for the acquired aversion to the CS. When animals were maintained with a fluid that differed from CS, on the other hand, it was found that conditioning context directly associated with the aversive event.