Avoidance but not aversion following sensory preconditioning with flavors: a challenge to stimulus substitution.

After two neutral stimuli have been paired (AB), directly conditioning a response to one of them (A) will also be reflected in a change in responding to the other (B). Standard accounts of this sensory preconditioning effect assume that it is mediated by a memory involving the stimulus that was directly conditioned (i.e., A). The reliance on this shared pathway implies that sensory preconditioning (involving B) and direct conditioning (involving A) should support qualitatively similar patterns of responding. In three experiments, directly pairing A with lithium chloride (LiCl) delivery resulted in both a reduction in consumption of A (i.e., avoidance) and a reduction in the size of licking clusters it elicits (i.e., aversion). In contrast, the sensory preconditioning effect resulted in a reduction in the consumption of B but no change in the nature of the licking response that it elicited; and a similar dissociation was observed after trace conditioning. These dissociations involving direct conditioning and sensory preconditioning, observed over a range of flavor concentrations and different doses of LiCl, undermine standard accounts of sensory preconditioning that are based on the assumption of stimulus substitution.