Role of the CS-US interval in the US preexposure effect.

Theory and research suggest that long delay taste-aversion conditioning should be less affected by proximal US preexposure than short-delay conditioning. The present research tested this hypothesis by administering illness-inducing LiCl shortly before a saccharin-LiCl pairing in which the postsaccharin LiCl was administered either immediately or 20 min. after access to saccharin. The results suggest that US preexposure has a more deleterious effect on conditioning when the illness-inducing US is delayed in conditioning than when it is immediate. These results are to be expected on the basis of classical conditioning principles and question theory and research that suggest more deleterious effects of US preexposure with shorter intervals between the preexposed and conditioning US.