Isohedonic tastes support a two-dimensional hypothesis of palatability.

The hypothesis that tastes activate two systems of palatability processing was tested by examining the ingestive and aversive fixed-action patterns (FAPs) elicited by equally preferred tastes. Berridge and Grill (1983) reported that the probability of occurrence of aversive FAPs could be increased without producing a reciprocal reduction in the probability of ingestive responses. This independence of ingestion and aversion was confirmed, and it was shown that the effect extends to measures of the actual quantity, as well as the probability, of the FAPs. It was further shown that ingestive and aversive FAPs could be increased together by simultaneously increasing the sucrose and quinine concentration of a taste. Equal preference between tastes may therefore need not imply identical hedonic evaluations, but rather simply an equivalent balance between ingestive and aversive systems. These data provide support for a two-dimensional hypothesis of palatability processing.