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At least 505 records · Page 28Linked to original sources
PubMed2003

Nonintentional task set activation: evidence from implicit task sequence learning.

Studies have shown that task sets could be configured endogenously (i.e., on the basis of memory) according to an explicit sequence or exogenously according to a task cue. In two experiments, we examined whether an implicitly learned sequence could facilitate task set configuration without participants' intention. These experiments led to opposite conclusions regarding this question, but their methodology made it impossible to distinguish between the interpretations. We altered the task-switching paradigm by embedding a hidden task sequence, while randomizing all other aspects, including perceptual (i.e., task cues) and motor elements. We found that a sequence of tasks, proper, was learned implicitly and that the memory of that sequence endogenously facilitated task decision processes without the participants' explicit knowledge.

Functional Laterality↗
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↗
PubMed2006

Can amnesic patients learn without awareness? New evidence comparing deterministic and probabilistic sequence learning.

Can associative learning take place without awareness? We explore this issue in a sequence learning paradigm with amnesic and control participants, who were simply asked to react to one of four possible stimuli on each trial. Unknown to them, successive stimuli occurred in a sequence. We manipulated the extent to which stimuli followed the sequence in a deterministic manner (noiseless condition) or only probabilistically so (noisy condition). Through this paradigm, we aimed at addressing two central issues: first, we asked whether sequence learning takes place in either condition with amnesic patients. Second, we asked whether this learning takes place without awareness. To answer this second question, participants were asked to perform a subsequent sequence generation task under inclusion and exclusion conditions, as well as a recognition task. Reaction times results show that amnesic patients learned the sequence only in the deterministic condition. However, they failed to be able to reproduce the sequence in the generation task. In contrast, we found learning for both sequence structures in control participants, but only control participants exposed to a deterministic sequence were successful in performing the generation task, thus suggesting that the acquired knowledge can be used consciously in this condition. Neither amnesic nor control participants showed correct old/new judgments in the recognition task. The results strengthen the claim that implicit learning is at least partly spared in amnesia, and the role of contextual information available for learning is discussed.

Adult↗
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↗
PubMed2006

Optimal decision making and the anterior cingulate cortex.

Learning the value of options in an uncertain environment is central to optimal decision making. The anterior cingulate cortex (ACC) has been implicated in using reinforcement information to control behavior. Here we demonstrate that the ACC's critical role in reinforcement-guided behavior is neither in detecting nor in correcting errors, but in guiding voluntary choices based on the history of actions and outcomes. ACC lesions did not impair the performance of monkeys (Macaca mulatta) immediately after errors, but made them unable to sustain rewarded responses in a reinforcement-guided choice task and to integrate risk and payoff in a dynamic foraging task. These data suggest that the ACC is essential for learning the value of actions.

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↗
PubMed2004

A new information processing measure for adaptive complex systems.

This paper presents an implementation-independent measure of the amount of information processing performed by (part of) an adaptive system which depends on the goal to be performed by the overall system. This new measure gives rise to a theoretical framework under which several classical supervised and unsupervised learning algorithms fall and, additionally, new efficient learning algorithms can be derived. In the context of neural networks, the framework of information theory strives to design neurally inspired structures from which complex functionality should emerge. Yet, classical measures of information have not taken an explicit account of some of the fundamental concepts in brain theory and neural computation, namely that optimal coding depends on the specific task(s) to be solved by the system and that goal orientedness also depends on extracting relevant information from the environment to be able to affect it in the desired way. We present a new information processing measure that takes into account both the extraction of relevant information and the reduction of spurious information for the task to be solved by the system. This measure is implementation-independent and therefore can be used to analyze and design different adaptive systems. Specifically, we show its application for learning perceptrons, decision trees and linear autoencoders.

Algorithms↗
PubMed2004

Voxel-based morphometry of comorbid schizophrenia and learning disability: analyses in normalized and native spaces using parametric and nonparametric statistical methods.

We employed voxel-based morphometry (VBM) to compare the distributions of grey matter found in structural magnetic resonance imaging (MRI) brain scans of patients with comorbid learning disability with schizophrenia, schizophrenia alone, learning disability alone, and normal controls. Our primary aim was to replicate a previous region of interest (ROI) finding that comorbids and schizophrenics belong to the same population. Nonparametric analysis in normalized space showed no significant differences in grey matter distribution between the comorbid and schizophrenia groups. Furthermore, this analysis showed significant grey matter reductions in the comorbid and schizophrenia groups when compared to the learning-disabled or the normal controls. Parametric analysis localized the significant grey matter reductions between the normal controls and the comorbid and schizophrenia groups to the prefrontal and temporal lobes. It also identified an area of increased grey matter, on the inferior aspect of the postcentral gyrus, in the learning-disabled alone compared to the other groups. Native space parametric and nonparametric analyses, based on modulation of the normalized scans, confirmed the similarity in grey matter distribution of the comorbid and schizophrenia groups. Results confirm the ROI finding that in native space the learning-disabled group possesses the least and normal controls the most grey matter for the cohort. An increase in the basal ganglia of patients with schizophrenia vs. the learning-disabled, probably attributable to antipsychotic medication, was identified in the native space analysis. The native space results did not however register statistically significant temporal lobe reductions found under normalized analysis between schizophrenics and normal controls. This may be attributable to minor physical anomalies (MPA) in the schizophrenic cranium. Overall, these VBM results replicate previous ROI findings and are compatible with the view that comorbid learning disability with schizophrenia is a severe form of schizophrenia, rather than a consequence of learning disability. VBM has the facility to compare grey matter distributions in this structurally diverse cohort.

Adult↗
PubMed1997

Age differences in implicit learning of higher order dependencies in serial patterns.

3 experiments examined serial pattern learning in younger and older adults. Unlike the usual repeating pattern, the sequences alternated between events from a repeating pattern and those determined randomly. The results indicated that no one was able to describe the regularity, but with practice every individual in all 3 age groups (including old old) became faster, more accurate, or both, on pattern trials than on random trials. Although this indicates that adults of all ages are able to learn second-order statistical dependencies in a sequence, age-related deficits were obtained in the magnitude of pattern learning. There were also age differences in what was learned, with only younger people revealing sensitivity to higher order statistical dependencies in the sequence. In addition, whereas younger people revealed evidence of their pattern learning in a subsequent conceptually driven production test, young-old and old-old people did not.

Adult↗
PubMed2004

Simulation of rat behavior by a reinforcement learning algorithm in consideration of appearance probabilities of reinforcement signals.

Brown and Wanger [Brown, R.T., Wanger, A.R., 1964. Resistance to punishment and extinction following training with shock or nonreinforcement. J. Exp. Psychol. 68, 503-507] investigated rat behaviors with the following features: (1) rats were exposed to reward and punishment at the same time, (2) environment changed and rats relearned, and (3) rats were stochastically exposed to reward and punishment. The results are that exposure to nonreinforcement produces resistance to the decremental effects of behavior after stochastic reward schedule and that exposure to both punishment and reinforcement produces resistance to the decremental effects of behavior after stochastic punishment schedule. This paper aims to simulate the rat behaviors by a reinforcement learning algorithm in consideration of appearance probabilities of reinforcement signals. The former algorithms of reinforcement learning were unable to simulate the behavior of the feature (3). We improve the former reinforcement learning algorithms by controlling learning parameters in consideration of the acquisition probabilities of reinforcement signals. The proposed algorithm qualitatively simulates the result of the animal experiment of Brown and Wanger.

Algorithms↗
PubMed2004

Impaired probabilistic category learning in hypoxic subjects with hippocampal damage.

Previous research has suggested that a probabilistic category learning task (e.g. weather prediction task) can be used to elucidate brain substrates of learning. We tested amnesic subjects with bilateral hippocampal damage due to hypoxia and matched controls on the weather prediction task and a variant, the "ice cream" task, which maintains a similar category structure. The hypoxic subjects were impaired relative to controls on both tasks; in the ice cream task, this difference was evident even early in training (first 50 trials). This finding is similar to functional neuroimaging (fMRI) studies in healthy subjects, which show medial temporal involvement even in early learning on this task. Additionally, strategy analysis of response patterns during learning suggest that the hypoxic group relied more heavily on simple, degraded learning strategies than did the control group. These results may suggest a qualification of the generally held conclusion that amnesic patients are not impaired at probabilistic category learning: at least under some circumstances, amnesic patients show an early and lasting deficit.

Adult↗
PubMed2002

Defining the neural mechanisms of probabilistic reversal learning using event-related functional magnetic resonance imaging.

Event-related functional magnetic resonance imaging was used to measure blood oxygenation level-dependent responses in 13 young healthy human volunteers during performance of a probabilistic reversal-learning task. The task allowed the separate investigation of the relearning of stimulus-reward associations and the reception of negative feedback. Significant signal change in the right ventrolateral prefrontal cortex was demonstrated on trials when subjects stopped responding to the previously relevant stimulus and shifted responding to the newly relevant stimulus. Significant signal change in the region of the ventral striatum was also observed on such reversal errors, from a region of interest analysis. The ventrolateral prefrontal cortex and ventral striatum were not significantly activated by the other, preceding reversal errors, or when subjects received negative feedback for correct responses. Moreover, the response on the final reversal error, before shifting, was not modulated by the number of preceding reversal errors, indicating that error-related activity does not simply accumulate in this network. The signal change in this ventral frontostriatal circuit is therefore associated with reversal learning and is uncontaminated by negative feedback. Overall, these data concur with findings in rodents and nonhuman primates of reversal-learning deficits after damage to ventral frontostriatal circuitry, and also support recent clinical findings using this task.

Adult↗
PubMed2006

Neural mechanism for stochastic behaviour during a competitive game.

Previous studies have shown that non-human primates can generate highly stochastic choice behaviour, especially when this is required during a competitive interaction with another agent. To understand the neural mechanism of such dynamic choice behaviour, we propose a biologically plausible model of decision making endowed with synaptic plasticity that follows a reward-dependent stochastic Hebbian learning rule. This model constitutes a biophysical implementation of reinforcement learning, and it reproduces salient features of behavioural data from an experiment with monkeys playing a matching pennies game. Due to interaction with an opponent and learning dynamics, the model generates quasi-random behaviour robustly in spite of intrinsic biases. Furthermore, non-random choice behaviour can also emerge when the model plays against a non-interactive opponent, as observed in the monkey experiment. Finally, when combined with a meta-learning algorithm, our model accounts for the slow drift in the animal's strategy based on a process of reward maximization.

Algorithms↗
PubMed2006

Sequence learning and selection difficulty.

The authors studied the role of attention as a selection mechanism in implicit learning by examining the effect on primary sequence learning of performing a demanding target-selection task. Participants were trained on probabilistic sequences in a novel version of the serial reaction time (SRT) task, with dual- and triple-stimulus participants having to ignore irrelevant items in the SRT display. Despite large performance decrements under dual- and triple-stimulus configurations, testing under single-stimulus conditions revealed no impairment to sequence learning. These findings suggest that implicit sequence learning is resistant to disruption of the selection process. Results are discussed in terms of a componential model of attention and in relation to the implicit-explicit distinction.

Adolescent↗
PubMed2004

A general role for early onset cues and intra-event learning; comment on McDonald and Siegel (2004).

Research on classical conditioning with drug unconditional stimuli has had a profound effect on the understanding of general conditioning processes. The experiment reported by R. V. McDonald and S. Siegel (see record 2004-10475-001) demonstrates that cues coincident with the onset of an event can become associated with the rest of the event. This sort of learning is probably ubiquitous and has been proposed as a mechanism behind the development of panic disorder, in which interoceptive cues coincident with the start of a panic attack can be associated with the rest of the attack and can eventually come to elicit full-blown panic on their own. Evidence that extinction exposure to early onset cues can reduce their power is especially important. Drug conditioning research continues to provide a powerful testing ground for important general principles of learning.

Conditioning, Classical↗
PubMed2005

What is preexisting strength? Predicting free association probabilities, similarity ratings, and cued recall probabilities.

Measuring lexical knowledge poses a challenge to the study of the influence of preexisting knowledge on the retrieval of new memories. Many tasks focus on word pairs, but words are embedded in associative networks, so how should preexisting pair strength be measured? It has been measured by free association, similarity ratings, and co-occurrence statistics. Researchers interpret free association response probabilities as unbiased estimates of forward cue-to-target strength. In Study 1, analyses of large free association and extralist cued recall databases indicate that this interpretation is incorrect. Competitor and backward strengths bias free association probabilities, and as with other recall tasks, preexisting strength is described by a ratio rule. In Study 2, associative similarity ratings are predicted by forward and backward, but not by competitor, strength. Preexisting strength is not a unitary construct, because its measurement varies with method. Furthermore, free association probabilities predict extralist cued recall better than do ratings and co-occurrence statistics. The measure that most closely matches the criterion task may provide the best estimate of the identity of preexisting strength.

Comprehension↗
PubMed2000

Memory effects of the Ca2+ and 5-HT antagonists dotarizine and flunarizine.

In experiments on Wistar and Long Evans rats, using behavioral methods for passive (step-down and step-through) and active (shuttle-box two-way avoidance with punishment reinforcement) the newly synthesized diphenyl-methyl-piperazine derivative with Ca2+ and 5-HT antagonistic action dotarizine (DOT) administered repeatedly at oral doses of 50 and 10 mg/kg in some cases improve memory process. Under the same experimental conditions the chemically related to dotarizine Ca2+ antagonist flunarizine significantly facilitated retention. In old (Long Evans and Wistar) rats DOT in large dose decreases values of learning criterion. Probably this is a manifestation of the inherent to drugs with nootropic action "therapeutic window". Earlier investigations of the same and other authors suggest the participation of serotonergic neurotransmission in the mechanism of the memory effects of the drug DOT.

Animals↗
PubMed2004

Gradient-based manipulation of nonparametric entropy estimates.

This paper derives a family of differential learning rules that optimize the Shannon entropy at the output of an adaptive system via kernel density estimation. In contrast to parametric formulations of entropy, this nonparametric approach assumes no particular functional form of the output density. We address problems associated with quantized data and finite sample size, and implement efficient maximum likelihood techniques for optimizing the regularizer. We also develop a normalized entropy estimate that is invariant with respect to affine transformations, facilitating optimization of the shape, rather than the scale, of the output density. Kernel density estimates are smooth and differentiable; this makes the derived entropy estimates amenable to manipulation by gradient descent. The resulting weight updates are surprisingly simple and efficient learning rules that operate on pairs of input samples. They can be tuned for data-limited or memory-limited situations, or modified to give a fully online implementation.

Algorithms↗