Independence of neophobia and taste aversion learning

Animals were presented with (1) one solution which differed from that of the test solution, (2) a series of distinctly flavored solutions whose flavors differed from that of the test solution, or (3) with a flavored solution whose flavor was the same as that of the test solution. When animals received the solution whose flavor was the same as that of the test solution prior to a test for neophobia and prior to a conditioning trial, neophobia was reduced and aversions were weakened. However, when animals received a solution or a series of solutions whose flavors differed from that of the test solution, neophobia was reduced but conditioned aversions were unaffected. Presentations of solutions that differed from the test solution following aversion formation left the association between the taste of the test solution and the effects of the aversion-inducing treatment intact. In a final experiment it was discovered that neophobia was reduced as much when animals drank solutions whose flavors changed every third day as when they drank the same solution throughout testing.     

Cross-modality transfer effects in conditioning-enhanced neophobia in chicks (Gallus domesticus): Evidence for the separability of novelty from specific stimulus characteristics

In this study, we investigated the separability of novelty from specific stimulus characteristics (e.g., color or taste quality) in the transfer of aversion effects. Ninety-six chicks (Gallus domesticus) received a novel visual (red water) or taste (3.0% vinegar) CS paired with an injection of lithium chloride or saline. The chicks were then tested for aversion to the CS or for conditioning-enhanced neophobia in response to a different novel visual cue (green water) or taste cue (1.0% saline). Aversions to the CSs were reliable and similar to each other. Reliable evidence of conditioning-enhanced neophobia occurred with respect to each test stimulus, irrespective of the type of CS, but conditioning with the vinegar CS produced reliably greater enhancement of neophobia than did conditioning with red water. For each CS, postconditioning neophobia was more persistent in testing with saline than with green water. The results for postconditioning neophobia suggested that novelty is a general stimulus property that is separable from specific stimulus characteristics.     

The basic tastants in aversion conditioning: Evidence for sensory preconditioning and not potentiation

In Experiment 1, a potentiation paradigm was used to test the relative influence of odor and taste with two 2 basic tastants (i.e., salt and sweet) in conditioned aversion learning. Experiment 1 showed that aversions to tastants (salt or sweet presented in a manner by which it could be tasted) were established only in subjects trained with the tastant, not the odor (i.e., salt or sweet presented in a manner by which it could not be tasted). Experiment 2 demonstrated, with a sensory preconditioning procedure, that the expression of an aversion to tastants was dependent on previous tastant experience prior to odor aversion training. These results suggest that while subjects can smell salt and sweet solutions, these odors are neither sufficient nor necessary for the expression of a conditioned tastant aversion.     

Effects of compound or element preexposure on compound flavor aversion conditioning

Two experiments with rat subjects examined conditioning of an aversion to a compound flavor stimulus after preexposing the compound, its constituent elements, or no explicit flavor stimulus. Experiment 1 used a short-term procedure in which preexposure and conditioning treatments occurred on the same day; Experiment 2 used a long-term procedure in which more extensive preexposure was administered several days before conditioning. In both experiments, preexposure of the elements slowed conditioning to the compound more than did preexposure of the compound itself. These effects were apparently not mediated by changes in pseudoconditioned or neophobic responses. The results were related to Lubow’s conditioned attention theory of stimulus preexposure effects.     

Higher order conditioning of a taste aversion

Two groups of rats each received 5 drops of NaCl solution from a dropper placed directly inside the mouth. The experimental group was then injected with lithium chloride to establish a conditioned taste aversion. The control group was injected 24 h later. After a recovery day the above procedures were repeated. On the next day both groups received 5 drops of a saccharin solution followed immediately by 5 drops of the NaCl solution. Subsequent preference tests established that the experimental group had learned an aversion to the saccharin solution as a result of its pairing with the NaCl solution which had previously been associated with poisoning. These results demonstrate that higher order conditioning of a taste aversion can be established using tastes as both the first-order stimulus and the second-order stimulus.     

A contingency analysis of taste aversion conditioning

The acquisition of conditioned taste aversion was assessed relative to five control procedures. That is, forward conditioning using multiple-trial, brief-duration taste CSs and weak USs over a 30-min CS-US delay was compared to backward, CS alone, US alone, sham CS and sham US, and random control procedures. The outcome supported an associative conditioning interpretation of the learned aversion. While there were no differences between the various control procedures, all were different from the forward conditioning group. The argument was made that some of the distinctive associative and nonassociative phenomena attributed to taste aversion conditioning (but not seen in the present study) may in part be due to the duration and intensity of both the CS and US events.     

Taste avoidance and taste aversion: Evidence for two different processes

The terms conditioned taste avoidance and conditioned taste aversion are often used interchangeably in the literature; however, considerable evidence indicates that they may represent different processes. Conditioned taste avoidance is measured by the amount that a rat consumes in a consumption test that includes both appetitive phases and consummatory phases of responding. However, conditioned taste aversion is more directly assessed with the taste reactivity test, which includes only the consummatory phase of responding. Rats display a conditioned taste aversion as conditioned rejection reactions (gapes, chin rubs, and paw treads) during an intraoral infusion of a nausea-paired flavored solution. Treatments that produce nausea are not necessary for the establishment of taste avoidance, but they are necessary for the establishment of taste aversion. Furthermore, treatments that alleviate nausea modulate neither the establishment nor the expression of taste avoidance, but they interfere with both the establishment and the expression of taste aversion. Considerable evidence exists indicating that these two measures are independent of one another. Taste avoidance may be motivated by conditioned fear rather than conditioned nausea, but taste aversion (as reflected by rejection reactions) may be motivated by conditioned nausea.     

Effects of distractor familiarity on habituation of neophobia

When the first presentation of a neophobic flavor is immediately followed by a distractor flavor, habituation of the neophobic response is typically attenuated. This is manifested by the fact that neophobia is still shown to the target flavor on its second presentation. Three experiments investigated the prediction that this effect will occur only for novel, but not familiar, distractor solutions. Experiments 1 and 2 found that, contrary to this prediction, both novel and familiar distractors can attenuate the habituation of a neophobic response. In Experiment 3, however, when the distractor was made very much more familiar, it lost its ability to interfere with the habituation of neophobia to the target solution. These results are discussed in terms of Wagner’s (1981) theory of habituation.     

Competition between ethanol-induced reward and aversion in place conditioning

Previous place conditioning studies in mice have shown that injection of ethanol immediately before a conditioned stimulus (CS+) produces conditioned preference, whereas injection of ethanol immediately after CS+ produces conditioned aversion. In the present experiments, we examined the learning that occurs when ethanol is injected in “ambiguous“ procedures that provide the opportunity for both types of conditioning. When ethanol was given midway through the CS (Experiments 1 and 2) or both before and after the CS (Experiment 3), the direction of place conditioning was the same as when mice were exposed only to whichever contingency occurred first (a primacy effect). That is, injection of ethanol in the middle of the CS conditioned aversion, whereas injection both before and after the CS conditioned preference. Because these results support the idea that ethanol elicits both aversive and rewarding effects, they are most consistent with conditioning theories that conceptualize unconditioned stimuli (USs) as events that can activate multiple representational components.     

Effects of pretraining on acquisition of novel configural discriminations in human predictive learning

In two experiments, participants acquired one of two target configural discriminations (a biconditional or negative patterning discrimination) in a predictive learning task. In Experiment 1, participants were pretrained with either a configural or an elemental discrimination; in Experiment 2, they were pretrained with a configural discrimination, an elemental discrimination, or a control discrimination that was not expected to bias them toward elemental or configural processing. In both experiments, acquisition of the target configural discriminations was faster after configural pretraining than after elemental pretraining. In addition, the negative patterning discrimination was acquired faster than the biconditional discrimination. Finally, the results of Experiment 2 were more consistent with the notion that elemental pretraining hindered acquisition of the target discriminations than with the notion that configural pretraining enhanced their acquisition. Implications of these findings are discussed.     

The effect of subadditive pretraining on blocking: limits on generalization

Recent evidence indicates that prior learning about a set of cues may determine how new cues are processed. If subjects are taught that two reliable predictors of an outcome do not summate when the cues are presented together (i.e., subadditive pretraining), the subjects will tend to show a less profound blocking effect when trained with different cues. Three experiments investigated the conditions necessary for subadditive pretraining to generalize to new cues. Experiment 1 demonstrated that subadditive pretraining is less effective in reducing blocking when it is experienced in a context other than that in which the blocking training is experienced. In Experiment 2, the effectiveness of subadditive pretraining waned with time. Experiment 3 showed that subadditive pretraining is more effective when the temporal characteristics of pretraining cues are similar to those of the cues used in blocking training. These results provide information concerning the conditions under which learning will generalize from one set of cues to another.     

Resistance to extinction of a learned taste aversion varies with time of conditioning

Sixteen rats were maintained out of doors in cages with natural light, temperature, and social stimulation for 3 months. Subsequently, by pairing the taste of sucrose with IP injections of LiCl, the rats were conditioned to avoid sucrose. Each of four groups of rats received the CS-US pairing at a different time of day. Times of conditioning were 6 a.m., 12 a.m., 6 p.m. and 12 p.m. EST. A two-bottle preference test between 4% sucrose solution and tap water was initiated 24-h after conditioning. Daily measurements of preference were continued for 16 consecutive days. Results indicated that, although all groups initially exhibited equivalent sucrose aversions, the groups conditioned at 12 a.m. and 6 p.m. extinguished within 12 days while the 6 a.m. and 12 p.m. groups continued to manifest profound aversions for sucrose throughout the 16 test days.     

Classical-classical transfer: Effects of prior appetitive conditioning upon aversive conditioning in rabbits

An appetitive-ayersive transfer experiment with rabbits determined that prior paired and unpaired tone CS and water US presentations, given in jaw-movement (JM) conditioning, respectively facilitated and retarded the acquisition of the nictitating membrane (NM) CR when the tone was subsequently paired with a shock US. In addition, the unpaired tone and water deliveries reduced the level of JM conditioning that was undertaken following the completion of NM CR acquisition. Finally, the reacquisition of the NM CR was accompanied by a large savings effect in contrast to the failure of the JM CR to display reacquisition savings. When the present findings are compared to the results of previous work addressing the influence of prior NM conditioning procedures upon subsequent JM CR acquisition, an asymmetry in appetitive-aversive interactions is indicated. This asymmetry encourages a reinterpretation of the opponent-process explanation of appetitive-aversive interactions. Moreover, the observed effects of the unpaired CS suggest the operation of a salience factor.     

Brain mechanisms for changes in processing of conditioned stimuli in Pavlovian conditioning: Implications for behavior theory

This article is a review of the results of a series of experiments designed to identify brain systems involved in appetitive conditioning of rats. It discusses some of their implications for behavioral theories of learning, especially those that concern changes in processing of conditioned stimuli (CSs). Evidence is presented which suggests that separable brain circuits are involved in (1) the production of CS-dependent conditioned orienting responses, (2) the enhancement of CS associability produced when expectancies about upcoming events are violated, (3) the reduction of CS associability produced when stimuli are consistent predictors of other events or are presented without consequence, and (4) the abilities of CSs to serve as reinforcers for second-order conditioning and to be sensitive to postconditioning changes in the value of the unconditioned stimulus (US). Finally, none of these circuits seems critical for normal acquisition of the most common indicator of Pavlovian conditioning, US-dependent conditioned responses (CRs). Although the independence of brain pathways does not demand independence of behavioral function, clustering of behavioral phenomena on anatomical grounds may provide useful guides for constructing behavior theories.     

A history of morphine-induced taste aversion learning fails to affect morphine-induced place preference conditioning in rats

Drugs of abuse have both rewarding and aversive effects, as indexed by the fact that they support place preferences and taste aversions, respectively. In the present study, we explored whether having a history with the aversive effects of morphine (via taste aversion conditioning) impacted the subsequent rewarding effects of morphine, as measured in the place preference design. In Experiment 1, rats were exposed to a taste aversion procedure in which saccharin was followed by morphine. Place preference conditioning was then initiated in which animals were injected with morphine and placed on one side of a two-chambered apparatus. Animals with a taste aversion history acquired place preferences to the same degree as controls without such a history, suggesting that morphine’s affective properties condition multiple effects, dependent on the specific stimuli present during conditioning. To determine whether these results were a reflection of processes operating in traditional associative conditioning, in a modified blocking procedure, place preference conditioning was attempted in the presence of a taste previously associated with morphine (Exp. 2). Under these conditions, animals still acquired morphine-induced place preferences comparable to those of animals without a morphine or conditioning history. These results are consistent with the position that drugs of abuse have multiple stimulus effects (positive and negative) that are differentially associated with specific stimuli (environmental and taste) that drive different behavioral responses (approach and avoidance).     

Solving Pavlov's puzzle: Attentional, associative, and flexible configural mechanisms in classical conditioning

This article introduces a new "real-time" model of classical conditioning that combines attentional, associative, and "flexible" configural mechanisms. In the model, attention to both conditioned (CS) and configural (CN) stimuli are modulated by the novelty detected in the environment. Novelty increases with the unpredicted presence or absence of any CS, unconditioned stimulus (US), or context. Attention regulates the magnitude of the associations CSs and CNs form with other CSs and the US. We incorporate a flexible configural mechanism in which attention to the CN stimuli increases only after the model has unsuccessfully attempted learn input-output combinations with CS-US associations. That is, CSs become associated with the US and other CSs on fewer trials than they do CNs. Because the CSs activate the CNs through unmodifiable connections, a CS can become directly and indirectly (through the CN) associated with the US or other CSs. In order to simulate timing processes, we simply assume that a CS is formed by a temporal spectrum of short-duration CSs that are activated by the nominal CS trace. The model accurately describes 94?% of the basic properties of classical conditioning, using fixed model parameters and simulation values in all simulations.     

Effects of CS amount on conditioned taste aversion at different CS-US intervals

Previous studies on the effect of CS amount/duration on the conditioning of taste aversion have reported that animals having greater contact with the CS acquire greater aversion. These findings appear to contradict studies of CS preexposure, which show that greater contact with the CS results in less aversion. In the present research, the effect of CS amount was shown to depend on the CS-US interval. Thus, a 10-ml CS (0.15% saccharin) at 3- and 9-h CS-US intervals produced less aversion than a 1-ml CS, but there was no significant effect of CS amount at a 30-min interval. These results suggest a two-process interpretation of the delay gradient in conditioned taste aversion: one process (learned safety) is dominant at relatively long CS-US intervals, and a different process becomes dominant at short intervals.     

Impact of brief or extended extinction of a taste aversion on inhibitory associations: Evidence from summation,retardation, and preference tests

In five conditioned taste aversion experiments with rats, summation, retardation, and preference tests were used to assess the effects of extinguishing a conditioned saccharin aversion for three or nine trials. In Experiment 1, a summation test showed that saccharin aversion extinguished over nine trials reduced the aversion to a merely conditioned flavor (vinegar), whereas three saccharin extinction trials did not subsequently influence the vinegar aversion. Experiment 2 clarified that result, with unpaired controls equated on flavor exposure prior to testing; the results with those controls suggested that the flavor extinguished for nine trials produced generalization decrement during testing. In Experiment 3, the saccharin aversion reconditioned slowly after nine extinction trials, but not after three. Those results suggested the development of latent inhibition after more than three extinction trials. Preference tests comparing saccharin consumption with a concurrently available fluid (water in Experiment 4, saline in Experiment 5) showed that the preference for saccharin was greater after nine extinction trials than after three. However, saccharin preference after nine extinction trials was not greater, as compared with that for either latent inhibition controls (Experiments 4 and 5) or a control given equated exposures to saccharin and trained to drink saline at a high rate prior to testing (Experiment 5). Concerns about whether conditioned inhibition has been demonstrated in any flavor aversion procedure are discussed. Our findings help explain both successes and failures in demonstrating postextinction conditioned response recovery effects reported in the conditioned taste aversion literature, and they can be explained using a memory interference account.     

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).