Alcohol-induced state-dependent learning: Differentiating stimulus and storage hypotheses

State-dependent effects of alcohol have been demonstrated in animals and man. Most studies have used tasks for which accurate performance typically requires that stimulus input was adequately stored initially and that the items were retrieved at the time of testing. Thus an alcohol-induced decrement in performance could be due to impaired storage, impaired retrieval, or both. The purpose of this experiment was to distinguish between stimulus and storage hypotheses of state-dependent learning (SDL). Sixteen subjects were used in a 2×2 design in which the task involved the learning and recall of a 19-item ‘route’ map. During initial learning, all subjects were sober. Immediately after learning, half the subjects were given a moderate dose of alcohol. Twenty-four hours later, all subjects were tested for recall under the same or different conditions. Greater retention was found for those subjects whose drug states were the same in memory storage/consolidation and retrieval. Thus an alcohol state effective during the memory consolidation interval following acquisition appears to be a sufficient condition for producing SDL. In this context, SDL might be better termed state-dependent memory storage and retrieval. The implications of these results for the aetiology and treatment of alcohol dependence are discussed.     

Extinction-induced neuroplasticity attenuates stress-induced cocaine seeking: a state-dependent learning hypothesis

Chronic drug use weakens excitatory neocortical input to the nucleus accumbens (NAc). We previously reported that extinction training, a form of inhibitory learning that progressively reduces cocaine-seeking behaviour when reward is withheld, reverses this deficit by up-regulating GluR1 and GluR2/3 subunits of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptors in the NAc. The level of GluR1 up-regulation is positively associated with a reduction in cocaine seeking, suggesting that extinction-induced up-regulation in AMPA receptors in the NAc opposes motivational influences that maintain cocaine seeking. This hypothesis is supported by the finding that over-expression of GluR1 and GluR2 in the NAc facilitates extinction of cocaine self-administration. Furthermore, a single extinction training session conducted during GluR1 and GluR2 over-expression strongly and selectively attenuates the ability of an environmental stressor to trigger relapse to cocaine seeking long after GluR1 and GluR2 over-expression declines. These results could suggest that excitatory input to the NAc promotes extinction learning, but only when memory is recalled under stressful situations. Recent studies indicate that both environmental stress and the frustrative stress of withholding reward during extinction of drug self-administration induce similar neurochemical events in the NAc. These neurochemical events could impose a "state-dependency" on extinction learning such that subsequent exposure to stress acts as a cue to enhance retrieval of extinction memory. Our results suggest that extinction-induced up-regulation in NAc AMPA receptors acts reciprocally to facilitate state-dependent extinction learning, as stressful situations evoke extinction memories that exert powerful inhibitory control over drug-seeking behaviour. These results may have important therapeutic implications for behaviour-based approaches aimed at treating drug addiction.     

Time course of free-choice priming effects explained by a simple accumulator model

Unconscious visual stimuli can be processed by human observers and modulate their behavior. This has been shown for masked prime stimuli that influence motor responses to subsequent target stimuli. Beyond this, masked stimuli can also affect participants' behavior when they are free to choose one of two response alternatives. This finding demonstrates that an apparently free-choice between alternative behaviors can be subject to influences that are outside of awareness. We report three experiments which exhibit that the temporal dynamic of free-choice priming effects corresponds to that of forced-choice priming effects. Forced-choice priming effects were relatively robust against variations of prime stimuli but sensitive to physical features of target stimuli. Free-choice priming effects, in contrast, depended largely on the stimulus-response compatibility of the prime. A simple accumulator model which accounts for forced-choice response priming can also explain free-choice priming effects by the assumption that unconscious stimuli can initiate motor responses when participants are engaged in a speeded choice-reaction time task. According to our analyses free-choice priming results from a response selection mechanism which integrates conscious and unconscious information from external, stimulus driven sources and also from internal sources.     

The potential role of state-dependent learning in cognitive therapy with spider phobics

Investigated the potential role of state-dependent learning in cognitive therapy with spider phobics. It was hypothesized that one strategy for increasing the effectiveness of cognitive therapy for anxiety would be to induce anxiety in subjects while they were learning the cognitive restructuring principles (i.e., during treatment). Thirty-two undergraduate volunteers were randomly assigned to one of six experimental conditions. Subjects in the five treatment conditions (the sixth was a no-treatment control condition) met for three sessions of cognitive restructuring,in vivo exposure, or a facts lecture (i.e., the placebo group). Results indicated that when working with spider phobics, three sessions of cognitive restructuring,in vivo exposure, or a facts lecture resulted in equal effectiveness immediately following treatment, but are more effective than no-treatment at all.     

Effects of reserpine on retention of escape reversal in mice: absence of state-dependent learning.

A discriminated escape training paradigm was used to study the effects of reserpine on learning and memory in mice. Intraperitoneal injection of reserpine before reversal training had no effect on acquisition but did produced a time-and dose-dependent impairment of retention test performance 10 days later. These results suggested that reserpine may have interfered with some aspect of memory storage. Retention impairments observed when a 2.0 mg/kg reserpine injection was given 2 hr before reversal training were not attenuated by readministering the drug before testing, a finding that provides no support for a state-dependency interpretation. Furthermore, animals treated with reserpine exhibited inferior retention of previous training, regardless of the pharmacological state present during that learning. This was interpreted as a drug-induced impairment of memory retrieval. In addition, performance during the initial discriminated escape training session suggested that reserpine may also impair acquisition under some conditions. In the last experiment, it was found that when the catecholamine precursor L-dihydroxyphenylalamine (100 mg/kg) and the indole amine precursor D,L-5-hydroxytryptophan (125 mg/kg) were both given after reserpine treatment, subsequent retention performance was not significantly impaired. The results are discussed in terms of the possible roles of biogenic amines in arousal, learning, and memory.     

Thirty-something categorization results explained: selective attention, eyetracking, and models of category learning

An eyetracking study testing D. L. Medin and M. M. Schaffer's (1978) 5-4 category structure was conducted. Over 30 studies have shown that the exemplar-based generalized context model (GCM) usually provides a better quantitative account of 5-4 learning data as compared with the prototype model. However, J. D. Smith and J. P. Minda (2000) argued that the GCM is a psychologically implausible account of 5-4 learning because it implies suboptimal attention weights. To test this claim, the authors recorded undergraduates' eye movements while the students learned the 5-4 category structure. Eye fixations matched the attention weights estimated by the GCM but not those of the prototype model. This result confirms that the GCM is a realistic model of the processes involved in learning the 5-4 structure and that learners do not always optimize attention, as commonly supposed. The conditions under which learners are likely to optimize attention during category learning are discussed.     

Effect of adrenocorticotropic hormone on conditioned avoidance in rats interpreted as state-dependent learning.

Rats were given one training trial that was followed 2 days later by one test trial in a "step-out" passive avoidance task. Each rat was injected with either adrenocorticotropic hormone (ACTH) or placebo before training and before testing. Four groups of rats were used, representing the 4 possible training-testing injection combinations: placebo-placebo, placebo-ACTH, ACTH-placebo, and ACTH-ACTH. ACTH given in testing increased avoidance for subjects that had received ACTH in training and decreased avoidance for those that had received placebo in training.     

Amnesic effect of cycloheximide in the mouse mediated by adrenocortical hormones.

The involvement of adrenocortical hormones in the amnesic effect of cycloheximide was examined in mice. Subcutaneous injection of cycloheximide shortly before a training trial of a passive avoidance task resulted in an amnesia of the avoidance response. However, amnesia was absent in the adrenalectomized animals in which cerebral protein synthesis was suppressed by cycloheximide. Injection of corticosteroids antagonized the amnesic effect, most effecively if the steroids were given immediately after training. The influence of the hormonal treatments upon the amnesic effect was not ascribable to a change in general activity level. The amnesic effect of subcutaneously injected cycloheximide appears to be mediated by hormonal deficiency, and not related to suppression of the cerebral protein synthesis.     

Drug effects: Agonistic and antagonistic processes

The research presented here has shown that tolerance to drugs can be accelerated by conditioning processes. Placebo effects may be considered the opposite of tolerance, and we have shown that placebo effects may be objectively recorded by physiological measures (electromyography, skin conductance responses, and event‐related potentials), as well as by behavioral and subjective methods. The placebo response, or more precisely, the expectation of drug effects, can add to the effect of the drug. Drug antagonistic expectations can also reverse the effect of the drug. There is some evidence that placebo effects are strongest when expectations are reinforced by administration of an active drug. Expectations have graded effects and may affect symptoms to a smaller or larger degree. Although drug effects can be considered stimuli, the investigation of the role of classical conditioning in drug use and drug effects involves special issues that must be carefully considered.     

Drug-preexposure effects in flavor-aversion learning: associative interference by conditioned environmental stimuli

Previous research has documented that exposure to a drug reduces the ability of the drug to support subsequent flavor-aversion learning. The four experiments reported here examined the hypothesis that this drug-preexposure effect is due to associative interference from environmental stimuli associated with the drug effects during preexposure. When distinctive environmental stimuli (confinement in a black compartment) were present during drug preexposure, these stimuli significantly disrupted subsequent flavor-aversion learning. Furthermore, flavor conditioning was not significantly disrupted when drug preexposure occurred in the absence of salient environmental stimuli or when the previously conditioned environmental stimuli were extinguished prior to flavor conditioning. It is significant, and in contrast to other published research, that flavor conditioning was not disrupted when the distinctive cues paired with the drug during preexposure were absent at the time of the flavor-drug pairing. These results are thus consistent with results from conventional studies of stimulus blocking and suggest that associative processes can play a major role in the drug-preexposure effect.     

The effects of intravenous diazepam and hyoscine upon human memory

Diazepam and hyoscine are known to have amnesic effects when administered intravenously. The two drugs are pharmacologically quite different from each other and might be expected to produce qualitatively distinct patterns of impairment in formal memory tasks. Groups of normal volunteers received intravenous administrations of diazepam, hyoscine and saline following a double-blind procedure and were then tested on immediate serial recall. Diazepam and hyoscine produced similar deficits on concrete and abstract words whether scored for ordered recall or item recall. In terms of ordered recall, phonemic similarity produced impaired performance under all three administrations, but semantic similarity did not. In terms of item recall, diazepam and hyoscine produced impaired performance on unrelated words, but the impairment was reduced under conditions of either phonemic or semantic similarity. There were also some interesting differences between diazepam and hyoscine in terms of their effects upon the shape of the serial-position curve and upon the types of intrusion error. The results confirm that both diazepam and hyoscine impair acquisition processes but fail to distinguish the effects of the two drugs upon different categories of encoding operations.     

社会比较中的认知偏差探析：“优于常人”效应和“差于常人”效应

近几年来,在社会心理学的研究中社会比较中的认知偏差现象越来越多的受到研究者的关注。该文主要介绍了社会比较中的认知偏差现象：“优于常人”效应和“差于常人”效应。并对其理论依据、测量方法以及研究的理论意义分别进行了介绍。最后,在对以往研究回顾的基础上,提出了对今后研究的展望。     

Observational learning: effects of bandwidth knowledge of results

The authors investigated whether bandwidth knowledge of results (KR) during observation of a model's performance enhances motor skill learning. Following a pretest, 2 groups of participants (N = 28) observed a model practicing a timing task. The bandwidth group received KR about the model's performance only when his performance fell outside the criteria for a correct response. The yoked group received KR on the same trials as the bandwidth group did but were not told that the KR was only about incorrect performances. In that way, the authors avoided a confound between bandwidth and relative frequency effects on performance and learning. Following the observation phase, both groups of participants performed 10-min and 24-hr retention tests. Bandwidth KR enabled that group to reduce its performance variability and, to a lesser extent, to enhance its performance accuracy. The authors discuss the results with respect to the powerful effect of qualitative KR through observation.     

Discriminative stimulus effects of diazepam and buspirone in normal volunteers.

A within-subject design was used to characterize the effects of dose manipulations on discriminative and self-reported effects of oral diazepam and buspirone. Subjects were trained to discriminate diazepam (10 mg) versus placebo (n = 10), or buspirone (10 or 15 mg) versus placebo (n = 9). The compounds were identified to subjects by letter code before discrimination training began. In later sessions, correct identifications at 2 hr after the oral administration of drug earned money. All subjects showed accurate discrimination performance during the test-of-acquisition phase. In a low-dose generalization phase, diazepam and buspirone produced dose-related increases in drug identifications across a four-fold range of doses. In a subsequent low-dose training phase, in which subjects were trained to discriminate progressively lower drug doses, the median lowest discriminable dose of diazepam and buspirone was 2.5 and 7.5 mg, respectively. Dose-response functions for drug identifications were shifted leftward in the low-dose training phase relative to the low-dose generalization phase, suggesting that reinforcement of progressively lower doses enhances drug discriminability. The self-reported effects of diazepam and buspirone were similar (e.g., both drugs increased ratings of drug strength and clumsy/uncoordinated) and different (e.g., diazepam but not buspirone increased ratings of drowsy/sleepy; buspirone but not diazepam increased ratings of tense/nervous). This study demonstrates discriminative and self-reported effects of diazepam and buspirone at doses lower than previously shown to be behaviorally active, and suggests that at commonly used clinical doses, diazepam is relatively more discriminable than buspirone.     

Between ignorance and truth: Partition dependence and learning in judgment under uncertainty

In 3 studies, participants viewed sequences of multiattribute objects (e.g., colored shapes) appearing with varying frequencies and judged the likelihood of the attributes of those objects. Judged probabilities reflected a compromise between (a) the frequency with which each attribute appeared and (b) the ignorance prior probability cued by the number of distinct values that the focal attribute could take on. Thus, judged probabilities were partition dependent, varying with the number of events into which the state space was subjectively divided. This bias was diminished among participants more confident in what they learned, was strong and insensitive to level of confidence when ignorance priors were especially salient, and required ignorance priors to be salient only when probabilities were elicited (not during encoding).