Single-trial taste aversion learning to water: a reassessment of familiarity, neophobia, and measurement stratedgies.

Abstract

Although a relatively new phenomenon, the learned taste a version paradigm has been extensive ly researched and applied to a rather impressive number of research areas. For example, Schweitzwer and Green (1982) used learned taste aversions to define better the developmental parameters of learning in preweanling rats. Similarly, Best and his colleagues (Cannon, Best, Batson & Feldman, 1983) have investigated learned taste aversions in cancer patients during chemotherapy. If the mechanism(sJ underlying such aversions can be understood, then techniques for interrupting and/or disrupting such associations might be developed. One interesting variant of basic research in this area has involved attempts to create learned taste aversions to plain tap water in rats. Research has indicated that a taste aversion to water may be developed if: 1) the animals are exposed to multiple CS-US pairings of water with an illness-inducing agent (Elkins, 1974); 2) if the animals have had NO previous experience with water (Garcia & Koelling, 1967); or 3) if the animals are presented with a second, safe taste prior to taste aversion conditioning to water (Elkins, 1974; Garcia & Koelling, 1967: Nachman, 1970). However, there are potential problems. First, Riley, Jacobs & Mastropaolo (1983) have argued that extensive preexposure (familiarity) of a taste attenuates subsequent aversion learning to that taste. Conversely, Nachman (1970) found that extensive preexposure did not significantly effect the strength of the learned aversion. Secondly, Garcia & Koelling (1967) and Elkins (1974) employed multiple CS-US pairings while Nachman used a single trial of water and illness. Finally, both single-bottle (Nachman, 1970) and two-bottle preference (Elkins, 1974) tests have been used, thus questioning the comparability of the various designs. The present studies were designed to more clearly delineate these issues. In all five experiments, rats were reared on water, shifted to a coffee solution (Group C) or continued on water (Group W) for 20 days, and then exposed to one pairing of water with Lithium Chloride (LiCl -an illness-inducing agent) in an attempt to establish a learned taste aversion to water. Experiments 1 and 2 employed a single-bottle consumption test to assess aversion learning and differed only with regard to the concentration of the coffee solution that was provided as a second, safe taste. Experiment 3 replicated Experiment 2 using the two-bottl~ preference test to evaluate aversion learning. Experiments 4 and 5 employed a Familiarity phase to evaluate more clearly the acquired aversion by equating the groups on their preference for coffee prior to testing. However, these experiments differed with regard to the strength of the coffee solution employed. As taste aversion learning was clearly shown under the two-bottle preference test, it is proposed that this type of measurement be emphasized in such studies. Further, the presentation of a second, safe taste prior to conditioning and/or testing appears to enhance subsequent aversion learning to water, although a neophobic response to the second taste is not necessary for this enhancement.