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At least 1,297 records · Page 72Linked to original sources
PubMed1994

[Prefrontal injection of the alpha 2-adrenergic antagonist yohimbine impairs performance of a delayed GO/NO-GO task in monkeys].

Two rhesus monkeys were trained to perform a delayed GO/NO-GO task, which was initiated by the monkey's pressing a lever. At 0.5 s after the lever-pressing, a white square (1.5 cm x 1.5 cm) was displayed on the right or the left of a computer screen and lasted 0.5 s as a cue. After a delay of 0.0-4.0 s, a red square (1.5 cm x 1.5 cm) appeared between the left-cue and right-cue positions as a signal for response choice. The monkey released the lever within 0.8 s if the cue had been on the right (GO trial), or kept on the lever-pressing for 1.2 s if the cue had been on the left (NO-GO trial). Short-term working memory during the delay was a non-spatially representational one. Local injection of the alpha 2-adrenergic antagonist yohimbine (10 micrograms) into the prefrontal cortex (Walker's areas 46, 9) contralateral to the performing hand decreased the correct rate of performance. The longer the delay period was, the more serious the impairment was. The performing error after injection of yohimbine was expressed mainly as "commissural" response (the monkey made GO response in NO-GO trial or NO-GO response in GO trial). Injection of the alpha 1-adrenergic antagonist prazosin (10 micrograms) or the beta-adrenergic antagonist propranolol (10 micrograms) did not impair the task-performance. Our results suggest that, prefrontal alpha 2-adrenoceptors may play an important role in the short-term working memory with non-spatial representation.

Animals↗
PubMedDate not supplied

Learning robot actions based on self-organising language memory.

In the MirrorBot project we examine perceptual processes using models of cortical assemblies and mirror neurons to explore the emergence of semantic representations of actions, percepts and concepts in a neural robot. The hypothesis under investigation is whether a neural model will produce a life-like perception system for actions. In this context we focus in this paper on how instructions for actions can be modeled in a self-organising memory. Current approaches for robot control often do not use language and ignore neural learning. However, our approach uses language instruction and draws from the concepts of regional distributed modularity, self-organisation and neural assemblies. We describe a self-organising model that clusters actions into different locations depending on the body part they are associated with. In particular, we use actual sensor readings from the MIRA robot to represent semantic features of the action verbs. Furthermore, we outline a hierarchical computational model for a self-organising robot action control system using language for instruction.

Language↗
PubMed1999

Three-dimensional shape and two-dimensional surface reflectance contributions to face recognition: an application of three-dimensional morphing.

We measured the three-dimensional shape and two-dimensional surface reflectance contributions to human recognition of faces across viewpoint. We first divided laser scans of human heads into their two- and three-dimensional components. Next, we created shape-normalized faces by morphing the two-dimensional surface reflectance maps of each face onto the average three-dimensional head shape and reflectance-normalized faces by morphing the average two-dimensional surface reflectance map onto each three-dimensional head shape. Observers learned frontal images of the original, shape-normalized, or reflectance-normalized faces, and were asked to recognize the faces from viewpoint changes of 0, 30 and 60 degrees. Both the three-dimensional shape and two-dimensional surface reflectance information contributed substantially to human recognition performance, thus constraining theories of face representation to include both types of information.

Discrimination Learning↗
PubMed2002

Hippocampal neurons responding to first-time dislocation of a target object.

To examine how hippocampal neurons respond to a mismatch between retrieved and actual experience, we trained rats to find a hidden platform at a particular location in an annular watermaze and then moved the platform. Several cells that were silent at the new platform location before the move fired vigorously when the rat found the goal. The new activity was paralleled by reduced discharge in a subset of simultaneously recorded interneurons. The pattern of activity returned toward its original configuration as the rat learned the new location. The activation of specific hippocampal neurons following dislocation of a target object may be essential for synaptic plasticity and adaptive modification of the animal's representation of the environment.

Action Potentials↗
PubMed1997

Neural correlates of motor memory consolidation.

Computational studies suggest that acquisition of a motor skill involves learning an internal model of the dynamics of the task, which enables the brain to predict and compensate for mechanical behavior. During the hours that follow completion of practice, representation of the internal model gradually changes, becoming less fragile with respect to behavioral interference. Here, functional imaging of the brain demonstrates that within 6 hours after completion of practice, while performance remains unchanged, the brain engages new regions to perform the task; there is a shift from prefrontal regions of the cortex to the premotor, posterior parietal, and cerebellar cortex structures. This shift is specific to recall of an established motor skill and suggests that with the passage of time, there is a change in the neural representation of the internal model and that this change may underlie its increased functional stability.

Adult↗
PubMed1995

Learning to ignore: psychophysics and computational modeling of fast learning of direction in noisy motion stimuli.

The effects of practice on the discrimination of direction of motion in briefly presented noisy dynamic random dot patterns are investigated in several forced-choice psychophysical tasks. We found that the percentage of correct responses on any specific task increases linearly with repetition of trials within roughly 200 trials from about chance to a performance of 90% or better. The level of performance remained constant or improved over several days, and in most instances it did not transfer when stimulus parameters changed. We used a modified Radial Basis Function (RBF) representation to model the psychophysical tasks. The performance of the model is functionally similar to the psychophysical results. We propose a Hebbian learning algorithm which deactivates the inputs from neurons responding to motion noise in the stimulus. Our computational model suggests that to solve this task in biological systems, neurons (perhaps in MT) improve their performance by 'learning to ignore' noise in the image.

Acoustic Stimulation↗
PubMed1997

Learning perceptual skills: behavioral probes into adult cortical plasticity.

Recent studies of the improvement of perceptual performance as a function of training - perceptual learning - have provided new insights into the neuronal substrates of this type of skill learning in the adult brain. Issues such as where in the brain, when and under what conditions practice-related changes occur are under investigation. The results of these studies suggest that a behaviorally relevant degree of plasticity is retained in the adult cortex, even within early, low-level representations in sensory and motor processing streams. The acquisition and retention of skills may share many characteristics with the functional plasticity subserving early-life learning and development. While the specificity of learning provides localization constraints, an important clue to the nature of the underlying neuronal changes is the time course of learning.

Adult↗
PubMed2004

Superior tactile performance and learning in professional pianists: evidence for meta-plasticity in musicians.

Musician's brains constitute an interesting model for neuroplasticity. Imaging studies demonstrated that sensorimotor cortical representations are altered in musicians, which was assumed to arise from the development of skilled performance. However, the perceptual consequences of the cortical changes remain elusive. Here we ask whether cortical reorganization induced by professional musical skill training is paralleled by the evolution of other, unrelated perceptual abilities. We therefore studied psychophysically tactile spatial acuity as an indirect marker of cortical changes in professional pianists and non-musician control subjects using a simultaneous two-point discrimination paradigm. We show that long-lasting piano practising resulted in lower spatial discrimination thresholds in comparison to non-musicians. In musicians, individual discrimination thresholds were linearly correlated with the daily training duration, indicating a direct link between tactile acuity and the degree of piano practising. To investigate whether the superior acuity in pianists is subject to further improvement, we used a Hebbian stimulation protocol of tactile coactivation known to improve spatial tactile acuity. Three hours of coactivation further reduced their discrimination thresholds. The coactivation-induced gain in pianists was significantly larger in comparison to control subjects and correlated with the years of heavy daily practising (>3 h/day), but not with the total years including casual playing. Our results suggest that despite already high-level performance in pianists, Hebbian learning was more effective in musicians than in controls. This implies stronger capacities for plastic reorganization and points to enhanced learning abilities implicating a form of meta-plasticity in professional pianists.

Adult↗
PubMed2006

A neural system for learning about object function.

Does our ability to visually identify everyday objects rely solely on access to information about their appearance or on a more distributed representation incorporating other object properties? Using functional magnetic resonance imaging, we addressed this question by having subjects visually match pictures of novel objects before and after extensive training to use these objects to perform specific tool-like tasks. After training, neural activity emerged in regions associated with the motion (left middle temporal gyrus) and manipulation (left intraparietal sulcus and premotor cortex) of common tools, whereas activity became more focal and selective in regions representing their visual appearance (fusiform gyrus). These findings indicate that this distributed network is automatically engaged in support of object identification. Moreover, the regions included in this network mirror those active when subjects retrieve information about tools and their properties, suggesting that, as a result of training, these previously novel objects have attained the conceptual status of "tools."

Adult↗
PubMedDate not supplied

The perceptual-mnemonic/feature conjunction model of perirhinal cortex function.

The perirhinal cortex was once thought to be "silent cortex", virtually ignored by researchers interested in the neurobiology of learning and memory. Following studies of brain damage associated with cases of amnesia, perirhinal cortex is now widely regarded as part of a "medial temporal lobe (MTL) memory system". This system is thought to be more or less functionally homogeneous, having a special role in declarative memory, and making little or no contribution to other functions such as perception. In the present article, we summarize an alternative view. First, we propose that components of the putative MTL system such as the hippocampus and perirhinal cortex have distinct and dissociable functions. Second, we provide evidence that the perirhinal cortex has a role in visual discrimination. In addition, we propose a specific role for perirhinal cortex in visual discrimination: the contribution of complex conjunctive representations to the solution of visual discrimination problems with a high degree of "feature ambiguity". These proposals constitute a new view of perirhinal cortex function, one that does not assume strict modularity of function in the occipito-temporal visual stream, but replaces this idea with the notion of a hierarchical representational continuum.

Animals↗
PubMed1998

Backward blocking and recovery from overshadowing in human causal judgement: the role of within-compound associations.

We replicated and extended a project by Dickinson and Burke (1996) that concerned human causal judgement. In a medical diagnostic setting, college students' ratings of the causal efficacy of target cues showed retrospective revaluation: relative to a proper control condition, ratings of target cues both increased ("recovery from overshadowing") and decreased ("backward blocking") during a second stage of training in which competing cues, but not target cues, were presented. These changes in causal judgements were exhibited only by subjects who had learned which target and competing cues were paired with one another during the first stage of training. These results cannot be explained by the Rescorla-Wagner (1972) model of associative learning, but they can be explained by the revised model of Van Hamme and Wasserman (1994); the revised model assigns non-zero salience to non-presented target stimuli whose memories or representations are retrieved by competing stimuli that had previously been paired with those target stimuli.

Adult↗
PubMed2002

Early experience is associated with the development of categorical representations for facial expressions of emotion.

A fundamental issue in human development concerns how the young infant's ability to recognize emotional signals is acquired through both biological programming and learning factors. This issue is extremely difficult to investigate because of the variety of sensory experiences to which humans are exposed immediately after birth. We examined the effects of emotional experience on emotion recognition by studying abused children, whose experiences violated cultural standards of care. We found that the aberrant social experience of abuse was associated with a change in children's perceptual preferences and also altered the discriminative abilities that influence how children categorize angry facial expressions. This study suggests that affective experiences can influence perceptual representations of basic emotions.

Case-Control Studies↗
PubMed2000

Feedback Delays: How Can Decision Makers Learn Not to Buy a New Car Every Time the Garage Is Empty?

Decision makers in dynamic environments (e.g., stock trading, inventory control, and firefighting) learn poorly in experiments where feedback about the outcomes of their actions is delayed. In searching for ways to mitigate these effects, this paper presents two computational models of learning with feedback delays and contrasts them against human decision-makers' performance. The no-memory model hypothesizes that decision makers always perceive feedback as immediate. The with-memory model hypothesizes that, over time, decision makers are able to develop internal representations of the task that help them to perform with delayed feedback. As borne out by human subjects, both models predict that a display of past history improves learning with delay and that increasing delay increasingly degrades performance. Even though the length of training in this task exceeds that used in many laboratory-based dynamic tasks, neither the two models nor the subjects are able to effectively learn without decision aids when faced with feedback delays. When given an amount of training that more closely approximates that provided in functioning dynamic environments, the with-memory model predicts that human decision makers may learn without decision aids over the long term if feedback delays are simple. These results raise several issues for continued theoretical investigation as well as potential suggestions for training and supporting decision makers in dynamic environments with feedback delays. Copyright 2000 Academic Press.

Journal Article↗
PubMed2004

Representation of number in animals and humans: a neural model.

This article addresses the representation of numerical information conveyed by nonsymbolic and symbolic stimuli. In a first simulation study, we show how number-selective neurons develop when an initially uncommitted neural network is given nonsymbolic stimuli as input (e.g., collections of dots) under unsupervised learning. The resultant network is able to account for the distance and size effects, two ubiquitous effects in numerical cognition. Furthermore, the properties of the network units conform in detail to the characteristics of recently discovered number-selective neurons. In a second study, we simulate symbol learning by presenting symbolic and nonsymbolic input simultaneously. The same number-selective neurons learn to represent the numerical meaning of symbols. In doing so, they show properties reminiscent of the originally available number-selective neurons, but at the same time, the representational efficiency of the neurons is increased when presented with symbolic input. This finding presents a concrete proposal on the linkage between higher order numerical cognition and more primitive numerical abilities and generates specific predictions on the neural substrate of number processing.

Animals↗
PubMed1998

Response channel activation and the temporoparietal junction.

When we learn to make one motor response to one visual stimulus and a different motor response to another, representations of these stimulus-response associations must be maintained to efficiently transduce perception into action. When an irrelevant distractor is presented adjacent to a target stimulus, interference is observed when the two stimuli are associated with conflicting responses, presumably due to response channel activation by the incompatible information. We have explored the neural bases of these interference effects. In a previous study, patients with hemispatial neglect showed normal interference from contralesional flankers. In another study, patients with lesions of the lateral prefrontal cortex were found not to show interference from distractors presented in the contralesional hemifield. The current study provided a more anatomically detailed investigation of the effects of posterior association cortex lesions on flanker interference. Patients with chronic, unilateral lesions involving the temporoparietal junction (TPJ), two of whom had hemispatial neglect, were compared with patients with lesions of the posterior association cortex not involving the TPJ. All patients performed a color discrimination task at fixation while a congruent or incongruent colored flanker was briefly presented (16.7 ms) in the adjacent contralesional or ipsilesional hemifield. Patients with TPJ lesions showed no interference effects from the contralesional flankers. These results suggest that the TPJ, in combination with the dorsolateral prefrontal cortex, is involved in transducing perception into action.

Aged↗