Noradrenaline loss and the disruption of between-CS stimulus generalisation effects in aversion learning

In stimulus blocking the previous conditioning to one stimulus, A, followed by conditioning to the compound stimulus, AB, results in less conditioning to the other stimulus, B. Three experiments were performed to study the effect of the prior pairing of a stimulus A (noisy bottle) with lithium chloride followed by stimulus AB (saccharin plus noisy bottle) and lithium chloride pairings upon the strength of the aversion to the target stimuls B (saccharin) in NA-depleted and control rats. The results obtained were not in keeping with a "blocking" explanation since enhancement, rather than blocking, of the saccharin aversion was obtained, and confirm several recent demonstrations of the "anti-blocking" effect from investigations using the conditioned suppression procedure. DSP4 treatment attenuated the aversion-enhancement ("anti-blocking") effects in all three experiments. The possibility that DSP4-induced noradrenaline depletions may cause some disruption of between-CS associations leading to a lesser higher order conditioning or stimulus generalisation is discussed and the present findings do add further evidence to the conclusion that noradrenaline is intimately involved in attentional processes.     

Context-dependent latent inhibition in taste aversion learning

The effects of taste stimulus preexposure, either in the presence or in the absence of a specific contextual cue consisting of a specific noise-producing bottle, upon the conditioning and testing of conditioned taste aversions to the taste (saccharin) plus context (noisy-bottle) compound stimulus were investigated. Four groups of rats were given preexposure trials (latent inhibition) to either: (1) novel saccharin in novel noisy bottles, (2) novel saccharin in familiar silent bottles, (3) familiar water in novel noisy bottles, (4) familiar water in familiar silent bottles, in six trials. During conditioning, saccharin was presented in the noisy bottles followed by lithium chloride for all the groups. At testing, saccharin was presented in the noisy bottles for both one-bottle and two-bottle tests of aversion. It was indicated that the conditioning decrement produced after both saccharin and noisy bottle preexposure was overwhelmingly greater than any produced after preexposure to the elements. These results, discussed in relation to current theories of latent inhibition and perceptual learning, further underline the overwhelming significance of exteroceptive contextual elements in conditioned taste aversions.     

Blocking in successive differential conditioning: Prior acquisition of control by internal cues blocks the acquisition of control by brightness

In each of four experiments the acquisition of discriminative stimulus control by brightness cues (black vs white runway) in a successive go/no-go instrumental discrimination was blocked in groups given prior discrimination training with internal (reward-produced and intertrial interval-related) cues as relevant discriminanda and brightness cues irrelevant. The blocking effects obtained here in instrumental conditioning were substantial and in most cases complete. Blocking occurred whether brightness in Phase I varied across trials but was uncorrelated with reinforcement (varied-irrelevant, V-I, condition) or whether all Phase 1 trials occurred to a single value on the brightness dimension (constant-irrelevant, C-I, condition) which then served as a redundant S+ cue in Phase 2 while the previously unexperienced brightness cue was added to the S- stimulus compound, or vice versa. Blocking in the V-I condition was shown not to be due simply to nondifferential reinforcement of brightness in Phase 1, but to depend on the prior acquisition of discriminative stimulus control by internal cues. As in Pavlovian conditioning, blocking here was an increasing function of amount of prior conditioning to the blocking stimulus. The results encourage the prospect that the procedures used here can be developed into a viable instrumental conditioning companion to the Pavlovian procedures now used almost exclusively to study blocking.     

Examination of factors which might disrupt a learned association between pentobarbital and LiCl

Injections of a sedative dose of pentobarbital (Pent) were followed 30 min later by injections of a toxic dose of lithium chloride (LiCl). As a result of these Pent →LiCl pairings, injections of Pent after consumption of saccharin solution failed to produce the usual saccharin aversion. This loss of the capacity of Pent to produce a flavor aversion is called Avfail. Experiment 1 showed that the Avfail effect was obtained with saccharin even though the rats consumed a novel vinegar solution prior to the Pent→LiCl pairings in Phase 1. This was surprising since the novel flavor was associated with the LiCl and ought to have overshadowed the association of Pent with LiCl. Experiment 2 showed that one set of Pent→LiCl pairings can produce two Avfail effects in sequence: the first with a novel flavor and the second with a flavor previously paired with LiCl sickness. It also showed that insertion of Pent injections and handling cues between the Pent→LiCl and the Flavor→Pent phases did not reduce the magnitude of Avfail. Experiment 3 showed that the Avfail effect was not disrupted by the insertion of 54 saline injections between the Pent→LiCl and Flavor→Pent pairings, nor by interposing 26 saline injections between each pair of Flavor→Pent trials. This seemed to exclude an important role for injection cues. Experiment 3 also showed that 4 exposures to Pent and 50 exposures to saline between the Pent→LiCl trials and the Flavor→Pent trials and 26 exposures to saline injections between each pair of Flavor→Pent trials did not reduce the magnitude of Avfail. The same exposure to Pent and saline injections did reduce the magnitude of the saccharin aversion shown by the LiCl→Pent group. These data are viewed as consistent with Lett's (Drug-drug associations: Evidence for the conditioning of a compensatory response. Paper presented at a meeting of the Eastern Psychological Association, New York, 1981) suggestion that Avfail represents a learned antisickness response.     

A pitfall for the expectancy theory of human eyelid conditioning

Two simple eyeblink conditioning experiments with random intermittent reinforcement schedules were performed. In Experiment 1, subjects had to rate their expectancy for an unconditioned stimulus (US) on a seven-level scale prior to each trial. As anticipated, expectancy for US increased with a successive conditioned stimulus (CS) alone, and decreased with successive CS-US pairings. However, Experiments 1 and 2 showed that the frequency of eyeblink conditioned responses (CRs) evolved in a direction opposite to that of expectancy changes: CRs increased, whereas expectancy for US decreased, and vice versa. The possible effect of sensitization on eyeblink response was ruled out by the lack of a run effect in an unpaired control group in Experiment 2. These results tend to disconfirm the expectancy theory of conditioning. Although they were explicitly predicted by the conventional “strength” theory of conditioning, an alternative interpretation is proposed within a cognitive framework.     

Effects of preexposure flavor concentration on conditioned aversion and neophobia

In Experiment 1, 128 experimentally naive, water-deprived rats (Rattus norvegicus) received pretraining access to either 0.25 or 1.5% saccharin, distilled water, or 2.0% saline, followed either by a pairing of 0.25 or 1.5% saccharin with an intraperitoneal injection of 0.15 M lithium chloride (LiCl) or by a pairing of distilled water with LiCl. Preexposure to either saccharin concentration reliably reduced conditioned aversion effects to 0.25% saccharin, relative to that for preexposure to distilled water or saline. But only preexposure to 1.5% saccharin reduced aversion effects to that concentration. In Experiment 2, 48 naive, water-deprived rats received preexposure procedures as in Experiment 1. Afterwards, the rats were tested for neophobia to 0.25 or 1.5% saccharin. Neophobia was reliably greater to the 1.5% concentration. However, preexposure to either saccharin concentration obliterated evidence for neophobia to saccharin, relative to that following preexposure to distilled water or saline.     

Discriminative properties of morphine that modulate associations between tastes and lithium chloride

Wistar rats learned to withhold consumption of a target solution when morphine preceded presentation of the target solution and lithium chloride (LiCl) and to consume the same target solution when saline preceded the presentation of the solution. After this serial feature discrimination training, morphine did not block the formation of a Pavlovian association between saccharin and LiCl but did suppress consumption of familiar tap water. After Pavlovian conditioning, morphine blocked the formation of an association between saccharin and LiCl but did not suppress consumption of a familiar tap water solution. The roles of morphine and saline can be interchanged. It appears that the morphine discriminative stimulus is calling up a representation of neither the conditioned stimulus nor the unconditional stimulus alone, but rather a modified representation of some aspect of their association.     

The effect of stimulus preexposure upon the context effect in taste-aversion learning in noradrenaline-depleted rats

The present investigation was designed to study the effect of preexposure to a saccharin plus noisy bottle stimulus compound, or to each element by itself, upon the extinction-dependent "context effects" (due to the presencelabsence of the noisy bottle contextual cue) in taste-aversion learning, following noradrenaline (NA) depletion via a single systemic DSP4 injection. Since contextual manipulations have provided a reliable means of studying selective attentional processes the current theorising on the role of noradrenaline can be effectively accommodated. It was found that, under the No Preexposure and Noisy Bottle Preexposure conditions, the "context effect" during the saccharin preference tests, after reinstatement of the noisy bottles for all groups, was totally absent for the NA-depleted rats; in the Saccharin plus Noisy Bottle Preexposure condition the "context effect" was partially blocked for the NA depleted rats and in the Saccharin Preexposure condition it was at least as strong as in the control condition, These findings may be interpreted as supporting our conclusions, concerning NA-depleted rats derived from several different investigations, i.e. that following NA loss rats fail to attend sufficiently to contextual cues in taste-neophobia and taste-aversion situations. Thus, the attentional deficit may be described as an inability to attend to all aspects of the taste stimulus plus exteroceptive context stimulus compound. Although the selective attentional hypothesis of noradrenaline function requires a good deal of alteration, it remains the most parsimonious account that can be described at present.     

Conditioned taste aversions support drug discrimination learning at low dosages of morphine.

The present experiment shows that a conditioned taste aversion procedure can support discrimination learning at dosages of morphine comparable to those required to produce motivational effects. Sprague-Dawley rats were injected with 4.0 mg/kg morphine sulfate prior to a saccharin-lithium chloride pairing, and physiological saline prior to a saccharin-saline pairing. The rats avoided the saccharin solution following the administration of morphine and consumed significantly more saccharin following saline administration after four discrimination cycles. After this initial discrimination the subjects were trained with progressively lower doses of morphine. Discrimination learning was apparent at doses of 2.0, 1.5, 1.0, 0.75 and 0.5 mg/kg. Animals initially trained with 1.0 mg/kg morphine also learned the discrimination but required 10 training cycles. After this initial discrimination the subjects were trained with progressively lower dosages of morphine and showed a discrimination at a dosage of 0.5 mg/kg.     

Conditioned and latent inhibition in taste-aversion learning: clarifying the role of learned safety.

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.     

Evidence for inhibitory associations between the unique elements of two compound flavours

In each of two experiments, rats were pre-exposed to two flavoured solutions, saline-lemon and sucrose-lemon. For group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution in a block, before any trials with the other. An associative theory suggests that the alternating, but not the blocked, schedule would establish an inhibitory association between sucrose and saline. To provide a retardation test of this inhibition, some animals in each group were then given a single pairing of saline and sucrose, experienced sodium depletion, and were finally tested for their consumption of sucrose. Sodium depletion increased consumption of sucrose more in group BLK than in group ALT. In groups given no saline-sucrose pairing, sodium depletion had only a small effect on sucrose consumption, which was the same in both groups. After multiple pairings of saline and sucrose, sodium depletion had an equally large effect on sucrose consumption in both ALT and BLK groups. These results imply that alternating pre-exposure to two compound solutions does establish an inhibitory association between their unique elements, and thus provide support for an associative theory of perceptual learning.     

Differential effects of two ways of devaluing the unconditioned stimulus after Pavlovian appetitive conditioning

Three experiments with rat subjects investigated the effects of two methods of devaluing a food unconditioned stimulus (US) after pairings of an auditory conditioned stimulus (CS) with that US. Experiment 1 found no effect of postconditioning pairings of the food US with lithium chloride (LiCl) on general activity to a tone CS, even though those pairings substantially reduced food consumption. Experiments 2 and 3 compared the effects on conditioned responding of postconditioning pairings of food with LiCl and with high-speed rotation. In these experiments the general activity measure was supplemented by a detailed visual analysis of the rats' behavior. Experiment 2 found that food-rotation pairings had larger effects than food-LiCl pairings on general activity responding and on two detailed behavioral measures but that food-LiCl pairings had larger effects on food consumption and on one behavioral measure. Experiment 3 replicated the findings of Experiment 2 and found that the ability of the CS to serve as a reinforcer for second-order conditioning after US devaluation was reduced more by food-LiCl pairings.     

Emergent Simple Discriminations and Conditional Relations in Children, Intellectually Impaired Adults,

Previous research has shown that when, under non-reinforced conditions, stimuli are added to S+ and S- stimuli in simultaneous discrimination tasks, transfer between paired stimuli is likely to occur. The present study examined whether this procedure also leads to the formation of conditional relations between paired stimuli. In Experiments 1, 2, and 3, normal pre-school children were trained on a simultaneous discrimination task with A1 reinforced and A2 not reinforced (A1+/A2- ). Then they received two tests (no programmed consequences): one with B stimuli superimposed on the A stimuli (A1B1/ A2B2), and one with B stimuli only (B1/B2). Subjects who selected A1B1 and B1 also received conditional discrimination tests: one with B1 or B2 as samples and A1 and A2 as comparisons (B-A), and one in which the functions of these stimuli were reversed (A-B). Intellectually impaired adults and normal adults served in Experiments 4 and 5, respectively. These experiments were basically the same except that the subjects were also given the opportunity to demonstrate transfer from B to C via BC (B1C1/B2C2 and C1/C2 tests). Most children (75%) and intellectually impaired adults (75%) treated the conditional discrimination probe tasks as simple discriminations and typically selected the trained and derived S+ stimuli. The remaining children, intellectually impaired adults, and all normal adults related all directly and indirectly linked stimuli of the same functions conditionally to one another (A-B, B-C, A-C, and vice versa). The present findings suggest that, as humans develop, conditional stimulus relations may emerge from tasks and stimulus configurations that are increasingly remote from traditional conditional discrimination tasks.     

Pavlovian conditioning with ethanol and lithium: effects on heart rate and taste aversion in rats

Rats received paired injections of either ethanol or saline as the conditioned stimulus and lithium chloride as the unconditioned stimulus (US) in a Pavlovian differential conditioning paradigm. Lithium chloride evoked a large deceleration in heart rate (80-100 beats per minute) as an unconditioned response. As a result of 10 conditioning trials, the substance paired with LiCl elicited a lower average heart rate than that elicited by the unpaired substance. Moreover, animals that received ethanol-LiCl injections subsequently were more averse to the taste of ethanol than animals receiving saline-LiCl pairings. However, there were no differences in ethanol's ability to serve as the US to induce an aversion to a novel flavor solution (i.e., the Avfail phenomenon was not observed). The overall pattern of results underscores the value of using multiple indexes of learning in drug-drug conditioning paradigms.     

Alternating exposure to two compound flavors creates inhibitory associations between their unique features

Rats were exposed to two compound solutions, saline-lemon and sucrose-lemon. In Group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution before any trials with the other. Previous retardation tests had implied that only alternating exposure would establish sucrose as an inhibitor of saline. To provide a complementary summation test for this inhibition, in Experiment 1, all the animals received pairings of peppermint and saline and were tested for consumption of peppermint-sucrose under sodium depletion. Consumption was increased by sodium depletion only in Group BLK. In Experiment 2, a retardation test was used to show that presentation of saline-lemon before sucrose-lemon on each exposure day would establish sucrose as an inhibitor of saline. Neither exposure to sucrose-lemon before saline-lemon nor alternating exposure to sucrose and saline alone had the same effect. These results provide support for an associative theory of perceptual learning that suggests that exposure to complex stimuli aids later discrimination partially as a result of establishing inhibitory associations between their unique elements.     

Is blockade of conditioned flavor aversions by chlorpheniramine the result of state dependency?

Conditioned flavor aversions induced by pairing flavored fluids with ionizing irradiation, lithium chloride, estrogen, or centrifugal rotation have been blocked by prior administration of chlorpheniramine. The blockade may be due to state dependency. This possibility was evaluated in the present experiment, which assigned female Long-Evans rats to a factorial combination of chlorpheniramine (20 mg/kg) vs saline during training, centrifugal rotation (150 rpm for 15 min) vs none as an UCS, and chlorpheniramine vs saline in testing. Rats conditioned with saline and rotation showed strong aversions when tested with either same or chlorpheniramine. Rats conditioned with chlorpheniramine and rotation showed no change during conditioning; when tested with saline they showed no aversion, and when tested with chlorpheniramine they showed no change from conditioning. Rats conditioned with either chlorpheniramine or saline and no rotation showed high fluid intake when tested with saline and reduced fluid intake when tested with chlorpheniramine. The results were interpreted as offering little support for state dependency.     

Contextual control in discrimination reversal learning

In 3 human predictive learning experiments, the authors examined contextual control of responding in discrimination reversal learning. In Phase 1, a discrimination between 2 stimuli (A+, B-) was trained in Context 1. During Phase 2, participants received discrimination reversal training (A-, B+) in Context 2. Testing occurred in Context 1 and Context 2 (Experiments 1A and 1B) or in Context 1 and Context 3 (Experiment 2). During the test phase, performance in Context 1 and Context 2 reflected the contingencies trained during Phase 1 and Phase 2, respectively. When testing occurred in Context 3, there was no discriminative responding between A and B. In addition, the experiments demonstrated that discriminating stimuli with a consistent reinforcement history were also affected by contextual manipulations. Results indicate that each training context acquires the ability to control performance. Unique-cue and configural approaches account for a major part of the results.     

Unconditioned stimulus devaluation effects in nutrient-conditioned flavor preferences

Experiments with different temporal relations between the conditioned stimulus (CS) and the unconditioned stimulus (US) in conditioning assessed whether US devaluation effects can be obtained after nutrient-conditioned flavor preference learning. One flavor (CScarb) was paired with a carbohydrate, Polycose; a 2nd flavor (CSprot) was paired with a protein, casein; and a 3rd flavor (CS-) was presented by itself. Following conditioning, one of the nutrients was devalued through pairings with lithium chloride in the absence of the CS flavors. In a subsequent 2-bottle test, rats preferred CScarb over CSprot; however, this preference was smaller when the carbohydrate was devalued than when the protein was devalued. Results suggest that CS flavors are able to form associations with the sensory features of nutrient USs under a wide variety of circumstances.     

Olfactory learning in the one-day old rat: reinforcing effects of isoproterenol

Within 24 h of their birth-induced norepinephrine surge, rat pups were tested for effects of a beta-receptor agonist, isoproterenol, on olfactory learning. Experiment 1 found no effect of isoproterenol on conditioning by pairing an odor (CS) with intraoral saccharin infusions. There was, however, unexpectedly strong responding in the unpaired control condition, which had the same contingency between the CS and isoproterenol as the paired condition. Experiment 2 found that pairings of odor and isoproterenol alone were sufficient for enhancing responding to the odor. Experiment 3 determined that isoproterenol had acted independently as a US for associative conditioning rather than facilitating nonassociative learning by mere exposure to the odor. These effects of isoproterenol as a US are consistent with the results of previous studies with older rats.     

Amount of training and cue-evoked taste-reactivity responding in reinforcer devaluation

In two experiments, rats received minimal (16) pairings of one auditory conditioned stimulus (CS) cue with a sucrose reinforcer, and extensive (112) pairings of another auditory CS with that reinforcer. After sucrose was devalued by pairing it with lithium chloride in some rats (Devalue groups) but not others (Maintain groups), taste reactivity (TR) and other responses to unflavored water were assessed in the presence of the auditory CSs alone. The minimally trained CS controlled substantially more evaluative TR responses than the extensively trained CS. Those TR responses were hedonic (positive) in the Maintain groups, but aversive (negative) in the Devalue groups. By contrast, food cup entry and other responses thought not to reflect evaluative taste processing were controlled more by the extensively trained cue. These responses were reduced by sucrose devaluation comparably, regardless of the amount of training. The results suggest rapid changes in the content of learning as conditioning proceeds. Early in training, CSs may be capable of activating preevaluative processing of an absent food reinforcer that includes information about its palatability, but that capability is lost as training proceeds.