US-preexposure effects in flavor-preference and flavor-aversion learning with nonnutritive USs

•We demonstrate the US preexposure effect with non-nutritive USs.•Preexposure to saccharin retards future learning when this cue is used as the US.•This same result was found when quinine was used as the US.•The role of habituation in preexposure effects is considered.•These effects challenge an interpretation in terms of blocking.

In two experiments, rats received exposure to either a saccharin or quinine solution followed by conditioning with a solution of almond as the conditioned stimulus (CS) and either saccharin or quinine as the unconditioned stimulus (US). In Experiment 1, rats received preexposure and conditioning using saccharin as the US; in Experiment 2 quinine was the US. In both cases the magnitude of the conditioning effect (an enhanced preference for the CS in Experiment 1; a reduced preference in Experiment 2) was reduced by preexposure to the US. The results provided confirmation of the occurrence of the US-preexposure effect in the flavor-preference procedure and demonstrate that the effect can be obtained with nonnutritive USs that lack significant post-oral consequences. The implications of these results for theories of the US-preexposure effect are discussed.