Michael R. Best

One bottle too many? Method of testing determines the detection of overshadowing and retention of taste aversions

A two-bottle testing method generally is regarded as a more sensitive measure of taste aversions than a one-bottle test. The current research compared the sensitivity of one-bottle and two-bottle tests in the detection of taste aversions. Specifically, the experiments were designed to detect both overshadowing (single- vs. compound-element conditioning) and retention interval (5 days vs. 1 day) effects. The groups tested with the one-bottle method evidenced both significant overshadowing and stronger aversions at 5-day retention intervals. On the other hand, the differences on these measures were not significant with the two-bottle tests. It is suggested that the efficacy of the two-bottle test be re-evaluated since it may obscure between-group differences in aversion strength.

Occasion setting of fluid ingestion by contextual cues

Abstract Pairing a familiar palatable fluid and a novel context with lithium chloride (LiCl) and presenting the fluid on non-LiCl-paired trials in the home cage resulted in contextual control of fluid consumption: consumption of the LiCl-paired fluid was reduced in the LiCl-paired context but not in the home cage. A nonpaired fluid was consumed normally in the paired context. These results are interpreted as evidence of occasion setting, i.e., the novel context signals a contingency between the fluid and toxicosis but is not itself associated with toxicosis. Pairing the novel context with LiCl prior to fluid-context-LiCl pairings enhanced the development of contextual control of consumption of the fluid. This enhancement is interpreted as summation of excitatory conditioning of the context with its occasion-setting function.

Enhancing the Expression of Flavor Neophobia: Some Effects of the Ingestion-Illness Contingency.

Four experiments investigating factors contributing to enhanced ingestional neophobia are reported. Rats administered lithium chloride following ingestion of a novel coffee solution showed an enhanced neophobia reaction to vinegar and casein. This enhancement was specific to the novelty of both the conditioning and test fluids and was not observed in animals receiving noncontingent toxicosis. Poisoning alone, however, mediated a nonspecific fluid suppression that persisted for approximately two drinking sessions following treatment. In contrast to other experiments, the operation of generalization was detected only when a novel flavor was the test fluid, suggesting that neophobia enhancement is at least partially mediated by a conditioned novelty aversion resulting from the novel flavor-lithium contingency.

Taste-mediated potentiation of noningestional stimuli in rats

Abstract Holtzman rats drank saccharin in a distinctive environmental chamber prior to lithium-induced toxicosis. This treatment was administered four times. These animals subsequently drank less water or familiar saline in the chamber than animals which received water in the environment during conditioning. In addition, these environmental stimuli blocked the formation of a lithium-mediated coffee aversion more if they were conditioned in the presence of saccharin than if they were conditioned in the presence of water. Such differential blocking provided further evidence that the presence of a taste during conditioning facilitated aversion learning to the environmental chamber.

Taste familiarity and apomorphine-induced taste aversions in humans.

Abstract Human volunteers learned taste aversions to a relatively novel cranberry flavor paired with apomorphine-induced illness. These aversions were significantly reduced by pretreatment familiarization to the flavor unless an unpalatable interfering flavor was introduced just prior to the administration of apomorphine. The outcomes have implications for taste-aversion learning in humans and for the control of flavor preferences in patients undergoing illness-inducing chemotherapy.

The effects of stimulus preexposure on taste-mediated environmental conditioning: Potentiation and overshadowing

On four occasions, Holtzman rats drank saccharin in a distinctive environment prior to lithium-induced toxicosis. Preconditioning exposure to saccharin either in the home cage or in the distinctive environment interfered significantly with the establishment of an environmental aversion. Animals preexposed to the experimental environment, however, showed environmental aversions substantially stronger than those in animals preexposed to saccharin and only slightly higher than those with no preexposure to either the taste or the environment. Subsequent saccharin tests revealed significantly stronger aversions in the group that received environmental preexposure than in any of the other groups. This pattern of outcomes demonstrates taste-mediated potentiation of novel and familiar environmental stimuli as well as overshadowing of the taste by novel environmental stimuli. Furthermore, it indicates that previous demonstrations of taste-mediated environmental potentiation involve facilitated conditioning of the environmental stimuli and decremented conditioning of the taste stimuli.

Extinguishing conditioned inhibition in flavour-aversion learning: effects of repeated testing and extinction of the excitatory element.

Three conditioned inhibition experiments using an A+/AX- design are reported in which lithium-mediated excitatory conditioning occurred to distinctive environmental stimuli and inhibitory conditioning to a vinegar flavour. Increased vinegar preferences were observed (i.e., conditioned inhibition) in each experiment, and these preferences extinguished with repeated testing as well as following extinction of the excitatory element. Vinegar preferences could be reinstated through reconditioning of the extinguished excitatory stimulus. These experiments speak to the status of inhibitory responding as a “slave” process to conditioned excitation.

Variations in the retention of taste aversions: Evidence for retrieval competition

In six experiments, we examined taste and compound taste/taste aversions at different retention intervals. In Experiment 1, saccharin aversions were significantly weaker 1 day after conditioning than 21 days after conditioning. This effect was determined not to be caused by the aftereffects of illness or differential hydration. With the use of a saccharin/denatonium compound, Experiment 2 demonstrated overshadowing of a denatonium aversion at 21- and 1-day retention intervals, Experiment 4 showed a potentiated saccharin aversion only at the 21-day retention interval, and both Experiments 2 and 4 revealed that the aversion of the taste-only controls was stronger at the later retention interval. Experiments 3 and 5 demonstrated that the differences at the two retention intervals were not caused by unconditioned changes in taste preference. Finally, Experiment 6 showed that extinction of the conditioning environment prior to testing results in stronger saccharin aversions than occur in nonextinguished controls. Collectively, these experiments suggest that testing within a 24-h period after conditioning will result in significantly weaker taste aversions. Also, these results support a retrieval-competition explanation that may account for the weakened aversions at the 1-day testing interval of both groups conditioned to single elements and those conditioned to compounds.

Interference with ingestional aversion learning produced by preexposure to the unconditioned stimulus: Associative and nonassociative aspects☆

Abstract Preconditioning exposure to a lithium chloride unconditioned stimulus (US) interferes with the subsequent conditioning of a taste aversion. Multiple US preexposures produce a long-lasting or durable interference with aversion learning, whereas a single US exposure produces a transient interference effect. The present experiments demonstrate that the durable US preexposure effect is substantially reduced if the method of drug treatment (infusion versus injection of the drug into the peritoneal cavity) or the spatial cues present during drug treatment (home cage versus a distinctive environment) are changed between the preexposure and taste conditioning phases of the experiment. In contrast, these manipulations do not attenuate the proximal/transient US preexposure effect. These findings indicate that different mechanisms are responsible for the two US preexposure effects. The results are consistent with previous suggestions that the durable effects of lithium preexposure are due to associative interference produced by the exteroceptive stimuli that accompany drug administrations and indicate that the proximal/transient US preexposure effect is mediated by nonassociative mechanisms.

Characteristics of the lithium-mediated proximal US-preexposure effect in flavor-aversion conditioning

Taste-aversion learning in rats is disrupted if the subjects are exposed to the unconditioned stimulus (US) shortly before the conditioning trial but not if this single US preexposure treatment occurs 1 day or more before conditioning. Several characteristics of this proximal US-preexposure phenomenon were explored. Experiment 1 showed that the time course of the interference with conditioning is directly related to the preexposure drug dose. Experiment 2 demonstrated that the interference effect is evident even if the test for aversion learning is conducted following a drug injection, thereby minimizing stimulus generalization decrement for the preexposed subjects. Finally, Experiment 3 showed that disruption of the contingent relationship between tastes and drug effects is probably not responsible for the proximal US-preexposure phenomenon because the interference with conditioning occurs regardless of whether or not the preexposure drug treatment is paired with a novel flavor. These findings, together with previous research, demonstrate the remarkably robust character of the proximal US-preexposure phenomenon.