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At least 1,657 records · Page 92Linked to original sources
PubMed1992

Sensory-motor coordination during grasping and manipulative actions.

Goal-directed grasping and manipulation of objects are human skills that depend on automatic sensory control in which predictive feed-forward mechanisms integrate somatosensory and visual signals with sensory-motor memory systems. Memory representations of physical and task-relevant properties of the object play a pivotal role. Anticipatory strategies are crucial when purposeful actions arise from learned relationships between afferent patterns and efferent commands. The development of even elementary precision grip skills is a protracted process not concluded until early adolescence. Not surprisingly, the neural control of manual actions engages most central nervous system areas known to be involved in motor control.

Fingers↗
PubMed2004

Flexible and abstract resolutions to crossmodal conflicts.

Participants judged whether two sequential visual events were presented for the same length of time or for different lengths of time, while ignoring two irrelevant sequential sounds. Sounds could be either the same or different in terms of their duration or their pitch. When the visual stimuli were in conflict with the sound stimuli (e.g., visual events were the same, but the sounds were different) performance declined. This was true whether sounds varied in duration or in pitch. The influence of sounds was eliminated when visual duration discriminations were made easier. Together these results demonstrate that resolutions to crossmodal conflicts are flexible across the neural and cognitive architectures. More importantly, they suggest that interactions between modalities can span to abstract levels of same/different representations.

Attention↗
PubMed2005

Electrophysiological correlates of temporal generalization: evidence for a two-process model of time perception.

In an event-related potential (ERP) study, brain correlates of temporal processing in the range of milliseconds were investigated by means of a dissociation paradigm. For this purpose, ten male and ten female subjects performed temporal and pitch generalization tasks with uni- and bidimensional stimulus variation. With difficulty held constant for both tasks, a larger frontally distributed negative slow wave was observed for pitch generalization relative to temporal generalization. This ERP pattern was consistent across uni- and bidimensional tasks of the present study but in direct contrast to prior ERP studies on temporal processing. Furthermore, for both uni- and bidimensional temporal tasks, within-task ERP analyses yielded amplitude modulation of centro-parietal P3b and fronto-central P500 as brain correlates of actively processed stimulus duration. Findings were consistent with a two-process model of temporal information processing based on a real-time comparison of the presented stimulus duration against an internal representation of the standard duration.

Adult↗
PubMed2005

Re-visiting the competence/performance debate in the acquisition of the counting principles.

Advocates of the "continuity hypothesis" have argued that innate non-verbal counting principles guide the acquisition of the verbal count list (Gelman & Galistel, 1978). Some studies have supported this hypothesis, but others have suggested that the counting principles must be constructed anew by each child. Defenders of the continuity hypothesis have argued that the studies that failed to support it obscured children's understanding of counting by making excessive demands on their fragile counting skills. We evaluated this claim by testing two-, three-, and four-year-olds both on "easy" tasks that have supported continuity and "hard" tasks that have argued against it. A few noteworthy exceptions notwithstanding, children who failed to show that they understood counting on the hard tasks also failed on the easy tasks. Therefore, our results are consistent with a growing body of evidence that shows that the count list as a representation of the positive integers transcends pre-verbal representations of number.

Association Learning↗
PubMed2004

Young children's sensitivity to probabilistic phonotactics in the developing lexicon.

A series of three experiments examined children's sensitivity to probabilistic phonotactic structure as reflected in the relative frequencies with which speech sounds occur and co-occur in American English. Children, ages 212 and 312 years, participated in a nonword repetition task that examined their sensitivity to the frequency of individual phonetic segments and to the frequency of combinations of segments. After partialling out ease of articulation and lexical variables, both groups of children repeated higher phonotactic frequency nonwords more accurately than they did low phonotactic frequency nonwords, suggesting sensitivity to phoneme frequency. In addition, sensitivity to individual phonetic segments increased with age. Finally, older children, but not younger children, were sensitive to the frequency of larger (diphone) units. These results suggest not only that young children are sensitive to fine-grained acoustic-phonetic information in the developing lexicon but also that sensitivity to all aspects of the sound structure increases over development. Implications for the acoustic nature of both developing and mature lexical representations are discussed.

Acoustics↗
PubMed2006

Linking implicit and explicit memory: common encoding factors and shared representations.

Dissociations between implicit and explicit memory have featured prominently in theories of human memory. However, similarities between the two forms of memory have been less studied. One open question concerns whether implicit and explicit memory share encoding resources. To explore this question, we employed a subsequent memory design in which several novel scenes were repeated once during an fMRI session and explicit memory for the scenes was unexpectedly tested afterward. Subsequently remembered scenes produced more behavioral priming and neural attenuation-two conventional measures of implicit memory-than did subsequently forgotten scenes. Moreover, brain-behavior correlations between these two implicit measures were mediated by subsequent memory. Finally, tonic activity, possibly reflecting the natural time course of attention, was predictive of subsequent memory. These results suggest that implicit and explicit memory are subject to the same encoding factors and can rely on similar perceptual processes and representations.

Adolescent↗
PubMed2005

Sleep-dependent motor memory plasticity in the human brain.

Growing evidence indicates a role for sleep in off-line memory processing, specifically in post-training consolidation. In humans, sleep has been shown to trigger overnight learning on a motor-sequence memory task, while equivalent waking periods produce no such improvement. But while the behavioral characteristics of sleep-dependent motor learning become increasingly well characterized, the underlying neural basis remains unknown. Here we present functional magnetic resonance imaging data demonstrating a change in the representation of a motor memory after a night of sleep. Subjects trained on a motor-skill memory and 12 hours later, after either sleep or wake, were retested during functional magnetic resonance imaging. Following sleep relative to wake, regions of increased activation were expressed in the right primary motor cortex, medial prefrontal lobe, hippocampus and left cerebellum; changes that can support faster motor output and more precise mapping of key-press movements. In contrast, signal decreases were identified in parietal cortices, the left insular cortex, temporal pole and fronto-polar region, reflecting a reduced need for conscious spatial monitoring and a decreased emotional task burden. This evidence of an overnight, systems-level change in the representation of a motor memory holds important implications for acquiring real-life skills and in clinical rehabilitation following brain trauma, such as stroke.

Adult↗
PubMed2003

Correlated neuronal discharges that increase coding efficiency during perceptual discrimination.

During a sensory discrimination task, the responses of multiple sensory neurons must be combined to generate a choice. The optimal combination of responses is determined both by their dependence on the sensory stimulus and by their cofluctuations across trials-that is, the noise correlations. Positively correlated noise is considered deleterious, because it limits the coding accuracy of populations of similarly tuned neurons. However, positively correlated fluctuations between differently tuned neurons actually increase coding accuracy, because they allow the common noise to be subtracted without signal loss. This is demonstrated with data recorded from the secondary somatosensory cortex of monkeys performing a vibrotactile discrimination task. The results indicate that positive correlations are not always harmful and may be exploited by cortical networks to enhance the neural representation of features to be discriminated.

Animals↗
PubMed1981

Mental measurement of line length: the role of the standard.

Reaction times were examined for magnitude estimates of line length. In the first two experiments, reaction times increased linearly with judged length. This result is consistent with the hypothesis the judgments are made by laying off a mental image of the standard along the line to be judged. The slope of the function relating judged length to reaction time was not affected by the length of the standard line, suggesting that the rate at which the image of the standard is laid off is not a function of the length of the standard. Reaction time also increased linearly with judged length when subjects judged line length when the standard of 1 in. was suggested but not provided as well as when no standard was suggested. The hypothesized laying-off process was compared to other cognitive manipulations, such as mental rotation and size scaling. Equivalence of judgments based on the representation of the standard in perceptual memory and in imagination is discussed.

Discrimination Learning↗
PubMed1989

Changes in activation levels with negation.

Three experiments investigated the effects of negation during on-line language processing. It was hypothesized that negation of a noun (e.g., no bread) would affect the activation level of the mental representation of that noun. Experiment 1 manipulated the location of the negation in sentences that were followed by a probe recognition task. Subjects were slower to indicate that a probe had been in the sentence when the probe corresponded to a negated noun. Experiment 2 replicated these results with a probe naming task. Experiment 3 replicated the result that reading the phrase no bread inhibits responses to bread in the probe task but found no evidence of inhibition of the response to an associate probe, such as butter. The results of these three studies suggest that negation affects the discourse focus of a noun phrase, and hence the activation level of its representation.

Adult↗
PubMed1992

Priming effects that span an intervening unrelated word: implications for models of memory representation and retrieval.

Several studies have reported priming effects that span an intervening unrelated word (Davelaar & Coltheart, 1975; Meyer, Schvaneveldt, & Ruddy, 1972). More recently, other investigators have suggested that such relatedness effects are the result of postaccess processes (Gough, Alford, & Holley-Wilcox, 1981; Masson, 1991; Ratcliff & McKoon, 1988). In fact, these investigators claim that when procedures are used that discourage the use of postaccess processes, relatedness effects do not span intervening unrelated words. The present experiments demonstrate reliable relatedness effects with procedures that eliminate postaccess processes. These results are consistent with the notion of spreading activation among local representations in memory. Implications for the issue of local versus distributed representations are discussed.

Adult↗
PubMed2001

Inferotemporal neurons represent low-dimensional configurations of parameterized shapes.

Behavioral studies with parameterized shapes have shown that the similarities among these complex stimuli can be represented using a low number of dimensions. Using psychophysical measurements and single-cell recordings in macaque inferotemporal (IT) cortex, we found an agreement between low-dimensional parametric configurations of shapes and the representation of shape similarity at the behavioral and neuronal level. The shape configurations, computed from both the perceived and neuron-based similarities, revealed a low number of dimensions and contained the same stimulus order as the parametric configurations. However, at a metric level, the behavioral and neural representations deviated consistently from the parametric configurations. These findings suggest an ordinally faithful but metrically biased representation of shape similarity in IT.

Action Potentials↗
PubMed1995

Amodal completion and vernier acuity: evidence of 'top-but-not-very-far-down' processes?

Vernier thresholds were measured by means of a forced-choice paradigm for physically separated bars that were perceived either as separate or as amodally completed behind an occluder. The finding that thresholds were not reduced (improved) with amodal completion argues against an early neural code for amodal completion that is equivalent to physical completion of the vernier bars (ie neural propagation/interpolation) and limits the stage at which amodal representations could arise via bottom-up processes to neural sites located centrally with respect to those involved in position coding. An alternative explanation is also considered, that this result reflects the activity of top-down processes that mediate amodal completion by imposing grouping/organizational constraints upon earlier representations of position. In support of this proposition it was found that when tested by means of a non-forced-choice paradigm without feedback, observers demonstrated a reduced tendency to report the presence of a vernier offset when the bars were perceived as amodally completed (ie a shift in response bias occurred). This separability of vernier acuity and response bias suggests the existence of 'top-but-not-very-far-down' grouping processes whose influence does not extend to early representations of relative position.

Analysis of Variance↗
PubMed1998

Multidisciplinary achievement: the collaborative approach to rapid cycle ICU and hospital change.

Multidisciplinary teams are different from the traditional team format in that representation and participation from various disciplines characterize the structure. In April 1996, a multidisciplinary group from Muhlenberg Regional Medical Center's intensive care unit learned methodology at the Institute for Health Care Improvement (IHI) Breakthrough Series in Adult Intensive Care. With the format learned, improvements in diverse areas such as ventilator management, intermediate care, clinical laboratory utilization, and others were accomplished. Continued support from an expert staff and utilization of on-line communication tools characterized this 15-month quality improvement endeavor. The end of the breakthrough series spurred the development of a hospital-wide collaborative cost containment team.

Clinical Protocols↗
PubMed2006

Role of centrifugal projections to the olfactory bulb in olfactory processing.

While there is evidence that feedback projections from cortical and neuromodulatory structures to the olfactory bulb are crucial for maintaining the oscillatory dynamics of olfactory bulb processing, it is not clear how changes in dynamics are related to odor perception. Using electrical lesions of the olfactory peduncle, sparing output from the olfactory bulb while decreasing feedback inputs to the olfactory bulb, we demonstrate here a role for feedback inputs to the olfactory bulb in the formation of odor-reward associations, but not for maintaining primary bulbar odor representations, as reflected by spontaneous odor discrimination.

Animals↗
PubMed1997

The French clinical guidelines and medical references programme: development of 48 guidelines for private practice over a period of 18 months.

The French medical profession and health insurance organizations have jointly committed themselves to a concept termed the 'medical regulation' of care. They decided to promote the quality of health care, judging that an approach based on quality was the best option for reducing the increase in health costs. The Clinical Guidelines and Medical References programme was entrusted to ANDEM (Agence Nationale pour le Développement de L'Evaluation Médicale). Fifty working groups (669 experts) and 50 reading groups (1643 experts) met from June 1994 to November 1995 to produce guidelines. Learned societies were involved to propose experts. Hospital practitioners, doctors who specialized in the topic in question and those who did not had equal representation in the groups. The method consisted of a review of the literature to determine the level of scientific evidence. ANDEM's Scientific Council suggested modifications to the groups and agreed to disseminate 48 of the 50 texts. Careful observation of the operation of the groups identified factors that can positively influence the nature of the discussions and help avoid conflict: an abundance of high-quality literature, an understanding of clinical research methodology, the existence of guidelines from different institutions or different countries tending towards the same conclusions, good initial work carried out by the chairperson and the project manager, a limit to the number of questions asked of the group, the chairperson having good people skills and meeting-management skills, and an absence of professional and financial consequences for the participants. Good management of working groups is an additional factor in ensuring success. The regulatory medical references programme has led to changes of behaviour within the medical profession.

Consensus Statements as Topic↗
PubMed2007

Dynamic instabilities as mechanisms for emergence.

That competences may emerge given appropriate environmental and behavioral context is a long-standing theme in developmental research. Work in the motor domain, but also in cognitive development, has made it possible to transform this idea into a mechanistic account closely linked to empirical evidence. In dynamic systems thinking, such capacities as keeping a motor goal in mind, remembering a location, or resisting a motor habit, are all understood in terms of the generation of stable patterns of neuronal activation. These may be input-driven, but also be stabilized by interactions within neuronal representations. A key theoretical insight is that whether a particular pattern of activation is stable or not is not determined by any single factor, learning process, or structural parameter. Instead, ongoing activity, recent activation history, current input, all may affect when a particular dynamic regime is reachable. In spite of such broad interdependence, sharp transitions may characterize the onset of a skill in any given context. Dynamic instabilities are the mechanistic basis for this phenomenon and thus form the basis for understanding development in terms of emergence. We exemplify the concepts of instability and emergence around the phenomenon of infant perseverative reaching and discuss implications for identifying key markers of development and their link to neuronal processes.

Child↗