John D. Batson

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.

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.

Taste preconditioning augments odor-aversion learning.

On the basis of previous work that has shown a taste can potentiate odor-aversion conditioning in AX+ conditioning, 6 experiments used rats to examine the effects of pairing a preconditioned taste (A) with a novel odor cue (X) in an A+/AX+ aversion conditioning design. Experiments 1A and 1B demonstrated that a preconditioned taste produced a robust odor aversion that was significantly stronger than a potentiated odor aversion. The results of Experiment 2 showed that the robust odor aversion produced by A+/AX+ conditioning was not the result of the potentiated odor aversion summating with generalization from the taste aversion. The augmented odor aversion was produced only when the taste and odor stimuli were presented simultaneously (Experiment 3) and the preconditioned taste aversion was intact at compound conditioning (Experiment 4). Pairing a novel odor with a preconditioned taste was not sufficient to condition an aversion to odor (Experiment 5), although other results implicated a role for an association between odor and taste in the odor augmentation effect (Experiment 6). The present results have implications for current models of taste + odor interactions in flavor-aversion conditioning.

Augmentation, not blocking, in an A+/AX+ flavor-conditioning procedure

An A+/AX+ Pavlovian conditioning design typically produces weakened or blocked conditioning to stimulus X. Two experiments were conducted in which rats first received an odor (A+) paired with an emetic US, and then received odor and taste (AX+) paired with the US. In both experiments, the preconditioned odorfacilitated conditioning to the taste. In Experiment 1, a group that received two odor-illness pairings in A+ conditioning had a stronger taste aversion than a group that only had a single odor-illness pairing. Experiment 2 demonstrated that the strengthened taste aversion in the A+/AX+ condition was not due to stimulus generalization. The results represent a unique outcome in the flavor-aversion literature that is similar to potentiation. We propose that this facilitated conditioning to X in the A+/AX+ design be termedaugmentation.

Augmentation of taste conditioning by a preconditioned odor.

Five experiments explored facilitated taste-aversion conditioning (odor-mediated taste augmentation), using rats that experienced odor (A) and taste (X) in an A+/AX+ design. Augmentation occurred when the stimuli were presented simultaneously during AX+ conditioning, and significantly weaker conditioning occurred after a sequential presentation (Experiment 1). Experiments 2 and 3 demonstrated that augmented conditioning decreased if the odor aversion was reduced through preexposure or extinction following A+ conditioning. A second-order conditioning explanation was not supported by the results of Experiment 4. Experiment 5 showed that extinction of the odor aversion after AX+ conditioning did not alter the strength of the augmented taste aversion. Odor-mediated taste augmentation is similar to potentiation, in which odor and taste cues operate in a synergistic, not competitive, manner.Five experiments explored facilitated taste-aversion conditioning (odor-mediated taste augmentation), using rats that experienced odor (A) and taste (X) in an A+/AX+ design. Augmentation occurred when the stimuli were presented simultaneously during AX+ conditioning, and significantly weaker conditioning occurred after a sequential presentation (Experiment 1). Experiments 2 and 3 demonstrated that augmented conditioning decreased if the odor aversion was reduced through preexposure or extinction following A+ conditioning. A second-order conditioning explanation was not supported by the results of Experiment 4. Experiment 5 showed that extinction of the odor aversion after AX+ conditioning did not alter the strength of the augmented taste aversion. Odor-mediated taste augmentation is similar to potentiation, in which odor and taste cues operate in a synergistic, not competitive, manner.

Foraging on the radial-arm maze: Effects of altering the reward at a target location

Thirsty rats were trained to collect small water rewards from the end of each arm of an eight-arm radial maze. During these training trials and subsequent testing trials, the subjects were allowed to choose a maximum of eight arms. “Preference” for a target maze location was studied by noting when, in the sequence of eight choices, the target was selected. During testing, when one maze location was consistently devoid of water, rats decreased their preference for this arm over trials (Experiment 1). Similarly, rats that learned a saccharin-lithium association demonstrated lower preferences for a maze location that consistently held the conditioned saccharin solution. This was true for animals that received saccharin-lithium conditioning on the maze (Experiment 3A) and for animals conditioned to saccharin in a separate context (Experiment 3B). An increase in preference for a target maze location consistently containing a sweet chocolate milk solution was observed in animals that were water- and food-deprived (Experiment 2). These studies demonstrate that animals will modify their responses toward (preferences for) maze locations that predictably contain an altered reward.

Interfering with taste aversion learning in rats: the role of associative interference.

Six experiments with rats investigated the conditions under which one flavor interferes with aversion conditioning to a second, familiar flavor. Conditioning to the familiar flavor was weakest when the interference flavor was contiguous to lithium-induced toxicosis, novel, more intense, and strongly associated with toxicosis. In addition, conditioning to the familiar flavor was weakened even if multiple conditioning trials were used. The repeated finding of an inverse relationship between strength of aversion to the target and interference flavors is interpreted as support for an associative competition hypothesis of the interference effect. The possible relevance of the interference effect to the attenuation of taste aversions in cancer patients is discussed.

Effects of repeated lithium injections on temperature, activity, and flavor conditioning in rats

Two experiments investigated the effects of lithium chloride on activity and rectal temperature in rats. Lithium injections, relative to saline injections in controls, caused decreases in both activity and temperature. Importantly, lithium’s effects did not diminish over the course of eight repeated injections, although preexposure to lithium did attenuate its conditioning effectiveness in a flavor-conditioning trial. The results support the idea that drug tolerance is not of great importance in the lithium-mediated US-preexposure effect in flavor conditioning.

Effects of postconditioning inflation on odor + taste compound conditioning

The within-compound association approach has been proposed as an account of synergistic conditioning in flavor aversion learning. One prediction from the within-compound association approach is that following taste + odor compound conditioning, postconditioning inflation of one element of the compound should increase responding to the second element. In four experiments with rats, the AX+/A+ design was used to determine whether postconditioning inflation of A would increase responding to X. In Experiments 1 and 3, responding to X was significantly stronger after AX+/A+ conditioning, as compared with AX+ conditioning. In Experiments 2 and 4, the specificity of the inflation effect was demonstrated, because AX+/A+ conditioning produced a stronger aversion to X than did AX+/B+ conditioning. Furthermore, it appears that the taste + odor association is symmetrical because inflation of the taste aversion increased responding to the odor (Experiments 1 and 2) and inflation of the odor aversion increased responding to the taste (Experiments 3 and 4).

Differences in taste-potentiated odor aversions with O+/OT+ versus OT+/O+ conditioning: Implications for configural associations

The present research demonstrates a conditioning order effect difference: Odor-aversion conditioning is stronger following OT+/O+ conditioning than following O+/OT+ conditioning with specific odor (O) and taste (T) cues. When a weak odor cue was used in Experiments 1A and 1B, OT+/O+ conditioning produced significantly stronger odor aversions than did either O+/OT+ or O+/O+ conditioning, which did not differ. The same design was used in Experiment 2 with a strong odor, but the order effect difference was not replicated, suggesting that the order effect difference is specific to conditions that produce taste-potentiated odor aversions. The interpretation that O+/OT+ conditioning is weaker because of the absence of a taste-odor within-compound association was not supported in Experiments 3 and 4. Notably, using stimuli that supported potentiation in earlier experiments, in Experiment 4, we found evidence of a taste-odor within-compound association in the absence of potentiation. These results confirm that previous theories of potentiation (within-compound association model, sensory-and-gate channeling model) are not sufficient to produce potentiation. Instead, these results are interpreted in terms of taste-odor configural associations.