Experiments 1-3 investigated the applicability of the classical conditioning concept of conditioned inhibition to taste-aversion learning. Rats made ill after drinking saccharin and subsequently administered a "safe" exposure to saline (or casein hydrolysate) evidenced an enhanced preference for the safe fluid (relative to either a third, slightly aversive, solution or to water) when compared to controls in which saccharin was not previously poisoned. Such active condition inhibition was significantly reduced in Experiment 4 when two safe exposures to saline preceded saccharin-illness pairings. These results indicate that conditioned inhibition can be established in a taste-aversion procedure and that a latent inhibition manipulation reduces the ability of a taste to become a signal for safety. Implications of these findings for the learned safety theory of taste-aversion learning and the relevance to bait-shyness of principles established within the classical conditioning paradigm are considered.

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.

Rats receiving two exposures to a casein hydrolysate flavor, the first either 45 min, 2 hr, or 4 hr before and the second 30 min before lithium-induced toxicosis, learned a lesser aversion than those receiving only the latter of the two exposures, 30 min prior to toxicosis. However, in a second experiment, as the interval separating the two presentations was increased beyond 3.5 hr, the deleterious effects of the initial presentation were diminished. In a third experiment of the two-presentation design, the functional conditioned stimulus was shown to be the initial exposure for intertaste intervals of approximately 4 hr and primarily the second exposure with longer (i.e., 11.5-hr) intervals. Taken together, the results indicate that the delay of reinforcement gradient in taste-aversion learning results primarily from processes more short-term in nature than those implied by learned safety.The ability of rats to associate ingestional stimuli with delayed drug-induced toxicosis is well documented, as is the delay of reinforcement gradient resulting from systematic increases in the flavor-toxin interval (e.g.,

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 twobottle 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.

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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.

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