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PubMed1992

Loss of the Kamin blocking effect in acute but not chronic schizophrenics.

Differences between research diagnostic criteria (RDC)-diagnosed acute and chronic schizophrenics and normal controls were studied using a Kamin blocking procedure. Blocking is an established animal learning procedure, thought by some researchers to reflect selective attention; decreased blocking indicates increased processing of irrelevant stimuli. It was predicted that this pattern would be obtained in acute schizophrenics, tested soon after admission, for two reasons: (1) evidence from previous clinical studies indicates that acute schizophrenics are more aware of nonsalient aspects of their environment than controls; and (2) blocking is disrupted in animals in a hyperdopaminergic state and restored by neuroleptic medication. This was the case: acute, but not chronic, schizophrenics showed disrupted blocking. This disruption was especially clear in those acute schizophrenics tested within 2 weeks of hospital admission. By the second test session (in a cross-over design), there was some evidence of normalization in performance in the acute schizophrenics. These findings are considered with regard to the dopamine hypothesis of schizophrenia.

Acute Disease↗
PubMed1992

Optimizing the use of information: strategic control of activation of responses.

Recent studies indicate that subjects may respond to visual information during either an early parallel phase or a later focused phase and that the selection of the relevant phase is data driven. Using the noise-compatibility paradigm, we tested the hypothesis that this selection may also be strategic and context driven. At least part of the interference effect observed in this paradigm is due to response activation during the parallel-processing phase. We manipulated subjects' expectancies for compatible and incompatible noise in 4 experiments and effectively modulated the interference effect. The results suggest that expectancies about the relative utility of the information extracted during the parallel and focused phases determine which phase is used to activate responses.

Adult↗
PubMed1995

Judging a book by its cover: interpretative effects of content on problem-solving transfer.

We examine how cover stories of isomorphic problems affect transfer. Existing models posit that people retain content in problem representations and that similarities and differences between the "undeleted" cover stories might interfere with recognition of structural similarities. We propose that cover stories can affect transfer in another way--by inducing semantic knowledge that modifies problem structures. Two experiments examined how people represent and solve permutation problems dealing with random assignment of elements from one set to elements from another set. Although the problems were structurally isomorphic, cover stories involving different pairs of element sets led subjects to abstract different "interpreted structures." Problems involving objects and people (e.g., prizes and students) led subjects to abstract an asymmetric structure ("get") and problems involving similar sets of people (e.g., doctors and doctors) led subjects to abstract a symmetric structure ("pair"). Transfer was mediated by similarities and differences between the interpreted structures of the learned and the novel problems.

Adult↗
PubMed1990

Health implications of drug interactions.

The awareness of the digoxin-quinidine interaction in the mid-70s led to increased interest in drug interactions. Much has been published on the subject in the form of interaction reports, handbooks, lists, cards, discs etc. However, only a few interactions in the literature have clinical significance and can be remembered by thinking in terms of groups, pharmacokinetics and probabilities. It is important to realise that drugs in a given class will have similar properties. Thus, phenylbutazone, like any other nonsteroidal anti-inflammatory drug (NSAID), is likely to potentiate the effects of warfarin. A knowledge of drug pharmacokinetics is also essential; a highly protein-bound drug may displace another when they are administered together. Remembering those drugs which induce liver enzyme formation will prevent their co-administration with drugs which have a critical dose-range. If a general practitioner can remember the few drugs in clinical practice with a narrow therapeutic index, he can consult a handbook before anything else is prescribed. Some interactions will rarely be encountered in daily general practice, i.e. those associated with tuberculosis treatment or anesthetic agents. Other interactions, e.g. the interaction between antihypertensive treatment and over-the-counter medication containing phenylpropanolamine, are more common. While most drug interactions can be avoided by thinking in terms of groups, pharmacokinetics and probabilities, some learning by rote is required, e.g. the potential for heart failure with concomitant beta-blocker and nifedipine therapy. In general, a schematic approach using thinking in terms of groups, pharmacokinetics and probabilities will prevent most clinically significant drug interactions; the rest can be avoided by consulting appropriate handbooks and specialists.

Animals↗
PubMed1995

YM796, a novel muscarinic agonist, improves the impairment of learning behavior in a rat model of chronic focal cerebral ischemia.

We studied effects of YM796, a novel muscarinic agonist, on behavioral, histological and regional cerebral blood flow changes in the chronic phase after focal cerebral ischemia in rats. YM796 (0.03, 0.1, 0.3 and 1 mg/kg) was administered orally once a day from the 7th to the 13th day after the permanent occlusion of left middle cerebral artery. On the 7th day, rats were trained in one-trial step-through passive avoidance task 45 min after drug administration. Test trials were carried out on the 8th and 14th days. Neurological deficits, including hemiplegia and abnormal posture, were observed on the 7th and 14th days. After the completion of behavioral studies, the rats were decapitated and cerebral infarction was measured. Regional cerebral blood flow was also measured by the hydrogen clearance technique 7 days after MCA occlusion. YM796 (0.1-1 mg/kg) significantly (P < 0.05) attenuated the impairment of learning behavior in a dose-dependent manner without affecting spontaneous locomotor activity. The ameliorating effect of YM796 (0.3 mg/kg) on the impaired learning behavior was significantly (P < 0.05) suppressed by intracerebroventricular injection of pirenzepine (10 micrograms/rat), an M1 antagonist. No significant difference in either neurological deficits or cerebral infarction was found between the vehicle- and YM796-treated groups. Further, YM796 (0.3 mg/kg) had little effect on the reduced blood flow in the ipsilateral frontal cortex 7 days after occlusion. These results suggest that YM796 improves the impaired learning behavior probably by activating central M1 receptors in a rat model of chronic focal cerebral ischemia.

Animals↗
PubMed1992

Conscious knowledge and changes in performance in sequence learning: evidence against dissociation.

Two experiments examined the relation between explicit knowledge and motor performance on the serial reaction time task developed by Nissen and Bullemer (1987). Tests of free recall and recognition of sequence components revealed that reliable explicit knowledge was acquired after an amount of practice that was hardly sufficient to improve mean motor performance. In addition, reaction time improvement was limited to the ending trials of the 3- and 4-trial sequence components that Ss recalled or recognized. These results were replicated in Experiment 3, in which Ss were trained under attentional distraction in the task developed by Cohen, Ivry, and Keele (1990). Overall, these findings undermine the most direct experimental support for the widespread view that conscious knowledge and performance in sequence-learning tasks tap 2 independent knowledge bases in normal Ss.

Adult↗
PubMed1994

Improving examples to improve transfer to novel problems.

People often memorize a set of steps for solving problems when they study worked-out examples in domains such as math and physics without learning what domain-relevant subgoals or subtasks these steps achieve. As a result, they have trouble solving novel problems that contain the same structural elements but require different, lower-level steps. In three experiments, subjects who studied example solutions that emphasized a needed subgoal were more likely to solve novel problems that required a new approach for achieving this subgoal than were subjects who did not learn this subgoal. This result suggests that research aimed at determining the factors that influence subgoal learning may be valuable in improving transfer from examples to novel problems.

Adult↗
PubMed1996

Learning to commit or avoid the base-rate error.

When predicting an event, people neglect overall frequencies (base rates) of various possibilities. We have previously shown that this base-rate occurs not only with word problems, but also in a procedure with repeated trials: a sample cue followed by two choice options, one of which the subject must choose, with feedback regarding the correctness of the choice. Perhaps this base-rate error depends on people's histories of matching physically similar items. In support of this suggestions, we begin by showing that the base-rate error is eliminated with physically unrelated items. We then show that when the relation between items is again arbitrary, but is a relation that subjects already know, the error reappears. Finally we show that teaching subjects new arbitrary relations reintroduces the error in later testing. These experiments demonstrate a fundamental base-rate error dependent on learned relationships without interference from re-existing associations between cues and options, predictions may be made more optimally.

Concept Formation↗
PubMed1992

Recognition of multiunit neural signals.

An essential step in studying nerve cell interaction during information processing is the extracellular microelectrode recording of the electrical activity of groups of adjacent cells. The recording usually contains the superposition of the spike trains produced by a number of neurons in the vicinity of the electrode. It is therefore necessary to correctly classify the signals generated by these different neurons. This paper considers this problem, and a new classification scheme is developed, which does not require human supervision. A learning stage is first applied on the beginning portion of the recording to estimate the typical spike shapes of the different neurons. As for the classification stage, a method is developed, which specifically considers the case when spikes overlap temporally. The method minimizes the probability of error, taking into account the statistical properties of the discharges of the neurons. The method is tested on a real recording as well as on synthetic data.

Action Potentials↗
PubMed1992

Combining exemplar-based category representations and connectionist learning rules.

Adaptive network and exemplar-similarity models were compared on their ability to predict category learning and transfer data. An exemplar-based network (Kruschke, 1990a, 1990b, 1992) that combines key aspects of both modeling approaches was also tested. The exemplar-based network incorporates an exemplar-based category representation in which exemplars become associated to categories through the same error-driven, interactive learning rules that are assumed in standard adaptive networks. Experiment 1, which partially replicated and extended the probabilistic classification learning paradigm of Gluck and Bower (1988a), demonstrated the importance of an error-driven learning rule. Experiment 2, which extended the classification learning paradigm of Medin and Schaffer (1978) that discriminated between exemplar and prototype models, demonstrated the importance of an exemplar-based category representation. Only the exemplar-based network accounted for all the major qualitative phenomena; it also achieved good quantitative predictions of the learning and transfer data in both experiments.

Concept Formation↗
PubMed1982

Learning impairment in the radial-arm maze following prolonged cannabis treatment in rats.

Chronic oral administration of cannabis extract to rats (daily delta 9-tetrahydrocannabinol dose 20 mg/kg) was examined in three experiments for its residual effect on radial-arm maze learning following a 1-month drug-free period. Learning a simple eight-arm maze was significantly impaired in rats treated for either 6 months (Experiment I) or 3 months (Experiment II) with the drug. In Experiment III, animals that received the extract for 3 months exhibited significant learning deficits on a much more difficult 12-arm radial maze. The results demonstrate that the deleterious effects of cannabis on radial-arm maze learning are probably due to a tendency toward increased vigilance and perseveration, possibly combined with an impaired utilization of spatial cues.

Animals↗
PubMedDate not supplied

[Influence of the probability of the random performance of an acquired reaction on the rate of the formation of an instrumental reflex].

Instrumental reflex formation in rats takes place more rapidly at high probability of random performance of instrumental reaction to light; however, it does not depend on the frequency of correct responses positive reinforcements (from 50 to 100%). In case of low probability, the learning process sharply slows down at 50% reinforcement of correct responses in comparison with 100% one.

Animals↗
PubMed1986

Learned helplessness as conditioned inattention to the target stimulus.

Learned helplessness theory explains the impaired performance that follows exposure to uncontrollable outcomes by assuming learned expectation of response-outcome independence that is transferred between tasks. Recent evidence has shown that introducing a second neutral stimulus, contingent on the offset of the uncontrollable stimulus, removes the subsequent interference. This finding has been claimed to support the view that the interference is a result of conditioned inattention rather than of the expectation of response-outcome independence. These conflicting explanations were examined in a series of four experiments that varied induction procedures (passive exposure or inescapability) and stimulus quality (aversive or nonaversive). All four experiments found the predicted interference, but only one, in which passive exposure was combined with an aversive stimulus, obtained results supporting the conditioned inattention hypothesis. We conclude that learned helplessness probably involves more than a single mechanism and that the passive exposure procedure may not be appropriate for demonstrating genuine helplessness deficits.

Adult↗