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 (Exp 1). Exps 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 Exp 4. Exp 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbohydrate-conditioned odor preferences in rats.

The effectiveness of odor cues to support nutrient-conditioned flavor preferences in rats was studied. When the rats drank fluid, the CS+ odor was paired with intragastric (IG) infusions of Polycose, and the CS– odor with IG water. In Experiment 1, rats trained with almond and anise odors presented with plain drinking water failed to acquire a CS+ odor preference. In contrast, rats in Experiment 2 formed a strong aversion to anise (or almond) paired with lithium chloride, which indicated that the odors were distinguishable to the rats. Experiment 3 showed that providing unique tastes (bitter or sour) in combination with the odors during training potentiated odor conditioning. The rats displayed a strong preference for the odor?+?taste CS+ and for the odor component alone. Experiment 4 showed that with another pair of odors (peppermint and vanilla), CS+ preferences could be conditioned in the absence of taste cues during training. These results demonstrate that rats can acquire strong nutrient-conditioned odor preferences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste-potentiated odor aversion learning based on amphetamine

This study sought to determine whether a taste can potentiate a conditioned odor aversion based on amphetamine as well as those based on lithium. A taste-potentiated odor aversion (TPOA) based on lithium was obtained in Experiment 1 only with a low concentration of an almond odor. This concentration was used in Experiment 2 where the taste, 0.1% saccharin, potentiated an odor aversion based on 1 mg/kg d-amphetamine. This was replicated in Experiment 3 where potentiation was found with doses of both 1 and 3 mg/kg amphetamine, and no effect of dose was detected. It was concluded that TPOA learning is not restricted to drugs such as lithium that produce conditioned unpalatability as well as conditioned aversions to a taste, because amphetamine does not produce conditioned unpalatability at the doses used here. Furthermore, because in Experiment 3 postconditioning extinction of the saccharin aversion removed the potentiation effect, it appears that this form of TPOA may depend on an association between the odor and taste, as proposed by within-compound theory.     

Odor of Taste Stimuli in Conditioned "Taste" Aversion Learning.

The present research addresses whether rats can express odor aversions to the odor of taste stimuli. In Experiment 1, saccharin or salt were either mixed in distilled water, so the rats could taste and smell them, or presented on disks attached to the tubes' metal spouts so the rats could only smell them. Aversions were established to taste stimuli under both conditions. The results of Experiment 2 indicate that conditioning was to the odor of the tastes when they were presented on disks in Experiment 1, hence both taste and odor aversions were established by means of "taste" stimuli. Taste aversion learning thus may more properly be termed flavor aversion learning, with flavor referring to both taste and odor components. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste-potentiated odor conditioning: Impairment produced by infusion of an N-methyl-D-aspartate antagonist into basolateral amygdala.

Two experiments examined the effects of infusing an N-methyl-D-aspartate (NMDA) receptor antagonist, d-2-amino-5-phosphonovalerate(d-APV), on taste-potentiated odor conditioning: a form of learning that is dependent on information processing in 2 sensory modalities. In Experiment 1, rats infused with d-APV were impaired in their acquisition of the potentiated learning to an odor cue. Expression of this learning and acquisition of a simple taste aversion remained intact following drug treatment. In Experiment 2, dose dependence and stereoselectivity were demonstrated for the antagonist compound. These results are consistent with previous studies demonstrating that either basolateral amygdala lesions, or treatment with NMDA antagonists, by other routes (systemic or intraventricular) produce selective deficits in taste-potentiated odor conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flavor-illness aversions: Gustatory neocortex ablations disrupt taste but not taste-potentiated odor cues.

Two studies evaluated the contribution of the gustatory neocortex (GN) to the potentiation of odor by taste during illness-induced aversions in 130 male Sprague-Dawley rats. In Exp I, Ss lacking GN and controls were given an odor, a taste, or an odor–taste compound cue followed by intragastric gavage of LiCl. Prior to conditioning, neophobia for flavored solutions was absent in Ss with GN lesions. After pairing with LiCl, GN Ss developed normal conditioned odor aversions, whereas conditioned taste aversions were attenuated or totally blocked. Potentiation of odor by taste after compound conditioning was evident in both control and GN Ss. In Exp II, normal Ss were given compound conditioning to induce potentiated odor aversions and then given GN lesions prior to tests with the odor and taste components. Taste aversion retention was totally disrupted by GN ablation; potentiated odor aversions were retained by both groups, although the GN group extinguished faster. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of temporal order and odor intensity in taste-potentiated odor aversions.

The role of the temporal order of odor and taste was studied in two experiments, and a third experiment studied the role of odor intensity in flavor-toxicosis conditioning with thirsty rats licking water spouts in a "wind tunnel." In all experiments, odors and tastes were presented for 2 min to rats, and 30 min later, a toxin (lithium chloride) was intubated. In Experiment 1, an odor was presented 90 s before, during, or 90 s after a taste to independent groups. Experiment 2 was a within-subjects partial replication of the first. Each rat was presented with one odor, then a taste, then a second odor with each stimulus separated by 45 s. The results of Experiments 1 and 2 indicated that (a) odor alone is not associated with illness under our conditions, (b) presenting an odor and a taste at the same time potentiates the odor component so that it is associated with illness, (c) 45-s and 90-s intervals between odor and taste eliminate potentiation, and (d) taste and odor interact asymmetrically; that is, odor has little effect on the development of taste-illness associations. In Experiment 3, an odor and a taste were presented simultaneously, and odor intensity varied. As odor intensity increased, the strength of the taste-potentiated odor aversion increased, whereas the aversion to the taste remained constant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of odor by taste in rats: Tests of some nonassociative factors.

Three experiments with 94 male Sprague-Dawley rats tested the contribution of nonassociative neophobia and sensitization to the potentiation of odor by taste. In Exp I, neophobia for almond odor (O), saccharin taste (T), and odor-taste compound (OT) cues was tested before and after noncontingent LiCl poisoning and compared with conditioned aversions produced by OT–LiCl temporal pairing. The OT compound potentiated unconditioned neophobia, but there was no evidence of poison-enhanced neophobia, disinhibition of neophobia, or sensitization by noncontingent LiCl; temporal pairing produced aversions for the compound and its elements. In Exp II, generalization to a novel odor was tested after O–LiCl or compound OT–LiCl pairing. The potentiated odor aversion did not generalize to the novel odor; it was specific to the odor paired with taste and LiCl. In Exp III, potentiation of the odor component by a discriminant or nondiscriminant taste component was tested. Potentiation was evident only when a novel discriminant taste was in compound with odor prior to LiCl poisoning. Results from all experiments support an associative "indexing" hypothesis of the potentiation effect in rats. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flavor-illness aversions: Potentiation of odor by taste with toxin but not shock in rats.

Paired almond odor or saccharin taste as a single CS or as a compound CS for both a footshock UCS and a toxin UCS (LiCl) to test the generality of potentiation in male Sprague-Dawley rats. Extinction tests with the almond and saccharin components were then given. In single CS–toxin experiments, taste was more effective than odor, and after compound conditioning, the taste component potentiated the odor component. Conversely, in single CS–shock experiments, odor was more effective than taste, and after compound conditioning, no potentiation was observed. Instead, interference effects were observed. In Exps I and II, the addition of taste disrupted odor CS–shock conditioning, and in Exp III, odor interfered with taste CS–shock conditioning. Visceral feedback was apparently a necessary UCS for the potentiation of odor by taste. Data support the neural convergence and gating hypothesis of flavor aversion conditioning. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus preexposure, comparison, and changes in the associability of common stimulus features

In four experiments, rats received preexposure either to both of two compound flavours (AX and BX), or to just one (BX). Experiment 1 demonstrated a perceptual learning effect, showing that, for animals given preexposure to both flavours, an aversion conditioned to AX generalized only poorly to BX. Subsequent experiments assessed the properties of the common feature, X. Experiment 3 showed that the two preexposure treatments did not differ in the extent to which they produced habituation of the neophobia evoked by X. Experiment 2 showed that conditioning to X proceeded more rapidly in subjects given preexposure to both AX and BX than in subjects preexposed to BX alone. In Experiment 4, a similar effect was found when the elements of the compounds were presented serially. It is concluded that the perceptual learning effect of Experiment 1 occurs in spite of the fact that preexposure to two stimuli tends to maintain the associability of their common elements.     

N-methyl-D-aspartate antagonist D-APV selectively disrupts taste-potentiated odor aversion learning.

Examined in 2 experiments the effects of the competitive N-methyl-{d}-aspartate (NMDA) antagonist {d}-APV ({d}-2-amino-5-phosphonovalerate) on rats' ability to acquire potentiated aversions to the odor element of a taste–odor compound. In Exp 1, pretreatment with {d}-APV (2.5 μg/side icv) caused stereospecific deficits in potentiated odor aversion learning but left simple taste and odor aversion learning intact. In Exp 2, pretreatment with {d}-APV had no effect on rats' acquisition of an illness-based odor discrimination task. These results parallel those previously obtained using a noncompetitive NMDA antagonist (G. S. Robinson et al, 1989) and show that interference with NMDA receptors can selectively impair potentiated odor aversion learning. These results suggest that NMDA receptors play a critical role in some, but not all, forms of learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative validity of contextual and discrete cues.

Contextual conditioning during relative validity training was explored in 3 experiments that used an appetitive Pavlovian conditioning preparation with rats. Magazine entries were the conditioned response. In Experiment 1, true-discrimination (TD: AX+, BX–) training generated weaker conditioning of X than did pseudodiscrimination (PD: AX+/–, BX+/–) training. The context showed a similar relative validity effect. Also, both PD training and simple partial reinforcement (X+/–) reduced contextual conditioning more than did unsignaled food, a demonstration of relative validity using partial reinforcement. Experiments 2 and 3 used within-subject and between-subjects designs, respectively, and showed that relative validity was determined by the summation of differences in conditioning to both the common element (X) and the context. The results are consistent with an attentional model or with a computational comparator model but not with the Rescorla-Wagner (R. A. Rescorla & A. R. Wagner, 1972) model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Supernormal conditioning.

In Experiment 1, rats received an A+AX° discrimination in which food was presented after Stimulus A by itself but not after a simultaneous compound of A with Stimulus X. AX was then paired with food in a 2nd stage, followed by test trials with A alone. Responding on the test trials with A was more vigorous than during a control stimulus that had been consistently paired with food. The remaining experiments were of similar design to Experiment 1, except that the 2nd stage also contained conditioning trials with X. The results from the test trials were essentially the same as for Experiment 1. The high level of responding during the test trials with Stimulus A is regarded as evidence of supernormal conditioning. Overall, the results are more consistent with a configural than an elemental theory of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhancement of responding to A after A+/AX+ training: Challenges for a comparator theory of learning.

Two appetitive Pavlovian conditioning experiments with rats investigated the associative changes that A undergoes in an A+/AX+ blocking procedure. Conditioned responding to A was enhanced relative to stimulus B, which had been conditioned in isolation (B+). This result was interpreted in terms of the formation of a within-compound association between A and X. The results of Experiment 2 supported this conclusion by demonstrating that X had associative strength of its own and, furthermore, that extinguishing X resulted in a similar level of responding to A and B. These results are considered in terms of retrospective revaluation theories of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual learning in flavor aversion: Evidence for learned changes in stimulus effectiveness.

Rats were exposed to the compound flavors AX and BX, presented in alternation, and to CX on a separate block of trials. Generalization to BX after aversion conditioning with AX was less than to CX. An equivalent effect was found when the nature of the common element was changed after preexposure but not when the common element was omitted during preexposure, during conditioning and test, or both. Rats conditioned with X alone again showed less aversion to BX than to CX; similarly, rats conditioned with a novel flavor (Y) showed less aversion to BY than to CY. These effects support the proposal that intermixed preexposure to AX and BX enhances the perceptual effectiveness of their unique features, A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overshadowing and associability change.

Three appetitive Pavlovian conditioning experiments with rats examined the associability of stimuli A and B that had a history of compound conditioning (AB+), relative to stimuli X and Y that had a history of conditioning in isolation (X+, Y+). Following this training, Experiment 1 revealed that conditioned responding was higher to X and Y than to A and B (overshadowing). In a subsequent AY+, AX?, BY? test discrimination, the AY/BY discrimination was solved more readily than the AY/AX discrimination. In Experiment 2, following AB+, X+, Y+ training, A and Y were presented as a compound and signaled the availability of reinforcement upon the performance of an instrumental response. Test trials in which A and Y were presented alone, and in extinction, revealed that A acquired greater control of instrumental responding than Y. Experiment 3 revealed that following AB+, X+, Y+ training, A and B served as more effective discriminative stimuli for instrumental responding than X and Y. Overall, these results imply that the associability of stimuli conditioned in compound is higher than stimuli conditioned in isolation. These results are discussed in terms of attentional theories of associative learning. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Context dependency of conditioned aversions to water and sweet tastes.

Three experiments exposed rats (Rattus norvegicus) to a discriminative conditioning procedure whereby a specific fluid was followed by lithium in one environment but not in another. This produced context-specific aversion to water, as detected by 2-bottle tests in Experiment 1, and a context-dependent saccharin aversion, which was unaffected by context extinction, in Experiment 2. Experiment 3 found that sucrose preexposure increased contextual control over the aversion established by sucrose-lithium pairings but had no effect on the target context. By contrast, target context exposure during conditioning reduced aversion to this context but did not affect contextual control of the sucrose aversion. In conclusion, depending on the conditioning procedures, contextual control of a taste aversion can be independent of the context's Pavlovian properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of UVB on the synthesis of complement proteins by keratinocytes

Conditioned taste aversion is a common classic conditioning procedure used to identify noxious stimuli. When a rat is given a taste solution, the conditioned stimulus (CS), followed by an unpleasant experience, the unconditioned stimulus (US), the rat will avoid consumption of the CS in future presentations. These experiments use the taste aversion procedure to examine the effect of exposure to a high magnetic field. A solution consisting of 3.0 g glucose and 1.25 g saccharin per 1 L of solution (G+S) was used as the CS and a 9.4-T magnet served as the US. In Experiment 1, all rats received a 10 min presentation of the G+S solution followed by either a 30 min exposure to the magnetic field (Magnet, n = 8), a 30-min exposure in a container with similar conditions but lacking the magnetic field (Sham, n = 8), or no exposure (Control, n = 8). The Magnet Group showed a taste aversion on the first day of preference testing (p < 0.05). Experiment 2 employed the same US-CS protocol for 3 consecutive days of conditioning. The Magnet Group demonstrated a taste aversion for the postexposure Days 1-8 (p < 0.01). There was no difference between the Sham and Control Groups in either experiment. The results of this study clearly demonstrate that the rats associated the G+S solution with the experience of being exposed to the high magnetic field and avoided the solution in subsequent presentations.     

Conditioned inhibition and superconditioning in an environment with a distinctive shape.

In Experiments 1 and 2a rats received an A+/AX? discrimination in a rectangular pool with two submerged platforms in diagonally opposite corners—the correct corners—for A+ trials. For AX? trials, rats were placed in the pool without the platforms but with identical landmarks, X, in the correct corners. Landmark X subsequently passed both a summation and retardation test for inhibition in Experiment 1. Upon completion of the discrimination in Experiment 2a, the platforms were placed near identical landmarks in the correct corners of the rectangle. The landmarks were those used for discrimination training for a superconditioning group (AX+ trials), but for a control group they were novel (AY+ trials). During a final test in the pool without the landmarks and the platforms, the superconditioning group spent more time than the control group searching in the correct corners. This finding, which was replicated in a kite-shaped pool in Experiment 2b, demonstrates successful superconditioning by landmark X of the cues created by the shapes of the pools. The results pose a problem for the theory of Miller and Shettleworth (2007). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resistance to extinction of conditioned odor perceptions: Evaluative conditioning is not unique.

A tasteless odor will smell sweeter after being sampled by mouth with sucrose and will smell sourer after being sampled with citric acid. This tasty-smell effect was found in experiments that compared odor-taste and color-taste pairings. Using odors and colors with minimal taste (Experiment 1), the authors found that repeated experience of odor-taste mixtures produced conditioned changes in odor qualities that were unaffected by intermixed color-taste trials (Experiment 2). An extinction procedure, consisting of postconditioning presentations of the odor in water, had no detectable effect on the changed perception of an odor (Experiments 3 and 4). In contrast, this procedure altered judgments about the expected taste of colored solutions. Evaluative conditioning (conditioned changes in liking) is claimed to be resistant to extinction. However, these results suggest that resistance to extinction in odors is related to the way they are encoded rather than to their hedonic properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)