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International audience; The amount of attentional resources necessary to walk in children, and how they evolve during childhood remains unclear. This study examined children's gait parameters in different dual-task conditions. 53 children, divided into two age groups (7-9 and 10-12 years old), and 18 adults walked on a mat in three different cognitive conditions: watching a video (video condition), listening its soundtrack (audio condition), and without any additional task (control condition). Questions were asked at the end of the video and audio conditions to make sure that participants were paying attention to the stimuli. A GAITRite® system was used for recording the gait data. Results showed an increase of velocity and step duration, and a decrease of cadence and percentage of double limb support duration from 7 years of age to adulthood during dual-task walking compared with single-task walking. This improvement seemed to be linear from 7 years to adults' age. The interference of dual-task on gait was larger for the video than for the auditory task and decreased with age. We concluded that walking requires a significant amount of attentional resources in children and that children rely more than adults on visual processes for walking.

International audience; The need for a better integration of the new generation of computer-assisted-surgical systems has been recently emphasized. One necessity to achieve this objective is to retrieve data from the operating room (OR) with different sensors, then to derive models from these data. Recently, the use of videos from cameras in the OR has demonstrated its efficiency. In this paper, we propose a framework to assist in the development of systems for the automatic recognition of high-level surgical tasks using microscope videos analysis. We validated its use on cataract procedures. The idea is to combine state-of-the-art computer vision techniques with time series analysis. The first step of the framework consisted in the definition of several visual cues for extracting semantic information, therefore, characterizing each frame of the video. Five different pieces of image-based classifiers were, therefore, implemented. A step of pupil segmentation was also applied for dedicated visual cue detection. Time series classification algorithms were then applied to model time-varying data. Dynamic time warping and hidden Markov models were tested. This association combined the advantages of all methods for better understanding of the problem. The framework was finally validated through various studies. Six binary visual cues were chosen along with 12 phases to detect, obtaining accuracies of 94%.

International audience; OBJECTIVE: The objective of this work is to introduce a set of similarity metrics for comparing surgical process models (SPMs). SPMs are progression models of surgical interventions that support quantitative analyses of surgical activities, supporting systems engineering or process optimization. METHODS AND MATERIALS: Five different similarity metrics are presented and proven. These metrics deal with several dimensions of process compliance in surgery, including granularity, content, time, order, and frequency of surgical activities. The metrics were experimentally validated using 20 clinical data sets each for cataract interventions, craniotomy interventions, and supratentorial tumor resections. The clinical data sets were controllably modified in simulations, which were iterated ten times, resulting in a total of 600 simulated data sets. The simulated data sets were subsequently compared to the original data sets to empirically assess the predictive validity of the metrics. RESULTS: We show that the results of the metrics for the surgical process models correlate significantly (p

International audience; The described experiment investigated whether adaptation to successive Achilles tendon vibration depends on the postural challenge. In phase 1, thirty-six participants were divided into three groups, each with a different postural challenge. After being blindfolded, participants received 15 trials of Achilles tendon vibration (10 s-90 Hz) while standing upright in either a free-standing condition (FS group), a light finger touch condition (LFT group), or a restrained-standing condition (RS group) in which a dorsal stand prevented body displacement. In phase 2, all participants were freely standing and received 15 additional trials of vibration. Antero-posterior trunk tilt was measured at the level of the trunk (C7). Although there were limited postural readjustments in LFT, adaptation was observed in phase 1 in both FS and LFT groups. In phase 2, the evoked postural displacement was greater in the RS group than in the other two groups. We concluded that although the absence of any postural challenge concomitant to the sensory stimulation prevented adaptation to occur, a minimal challenge was sufficient.

International audience; We study the time evolution of a neural network model as it learns the three stages of a visual delayed-matching-to-sample (DMS) task: identification of the sample, retention during delay, and matching of sample and target, ignoring distractors. We introduce a neurobiologically plausible, uncommitted architecture, comprising an "executive" subnetwork gating connections to and from a "working" layer. The network learns DMS by reinforcement: reward-dependent synaptic plasticity generates task-dependent behaviour. During learning, working layer cells exhibit stimulus specialization and increased tuning of their firing. The emergence of top-down activity is observed, reproducing aspects of prefrontal cortex control on activity in the visual areas of inferior temporal cortex. We observe a lability of neural systems during learning, with a tendency to encode spurious associations. Executive areas are instrumental during learning to prevent such associations; they are also fundamental for the "mature" network to keep passing DMS. In the mature model, the working layer functions as a short-term memory. The mature system is remarkably robust against cell damage and its performance degrades gracefully as damage increases. The model underlines that executive systems, which regulate the flow of information between working memory and sensory areas, are required for passing tests such as DMS. At the behavioural level, the model makes testable predictions about the errors expected from subjects learning the DMS.

Azouvi P, Olivier S, de Montety G, Samuel C, Louis-Dreyfus A, Tesio L. Behavioral assessment of unilateral neglect: study of the psychometric properties of the Catherine Bergego Scale. Arch Phys Med Rehabil 2003;84:51-7. Objective: To assess the psychometric properties of a scale for spatial neglect in everyday life. Design: Validation study. Setting: A neurologic rehabilitation unit in a university hospital. Participants: Eighty-three consecutive right-hemisphere stroke patients. Interventions: Not applicable. Main Outcome Measures: The Catherine Bergego Scale (CBS) was used to assess neglect behavior and anosognosia. Its sensitivity was compared with that of 3 conventional tests. The inner structure of the scale was studied by principal component analysis. In addition, linearity, unidimensionality, and reliability of the scale were tested through Rasch analysis. Results: Behavioral assessment correlated significantly to, but was more sensitive than, conventional tests. Anosognosia correlated significantly with neglect severity, although individual dissociations occurred. Factorial analysis disclosed a single underlying factor, explaining 65.8% of total variance. Rasch analysis also revealed that the 10 items defined a common, single ability continuum with widespread measurement range and quite regular item distribution, and showed a satisfactory reliability. Conclusion: Behavioral assessment proved to be more sensitive than conventional paper and pencil tasks. Both conventional statistics and Rasch analysis suggest that the CBS is reliable and valid, and that the 10 items define a homogeneous construct. [copy ] 2003 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Objective The aim of this study was to investigate whether a high-intensity warm-up at the start of a graded, symptom-limited exercise test would enhance heart rate reserve and thus improve the aerobic performance of orthotopic heart transplant patients. Design Adrenal and cardiorespiratory responses were compared in 10 orthotopic heart transplant patients who performed two graded, symptom-limited exercise tests on an ergocycle. Results At the start of the graded, symptom-limited exercise test, high intensity increased the norepinephrine level more than usual intensity between rest and the third minute of exercise. This higher norepinephrine level was followed by a higher heart rate response from the fourth minute of exercise. Heart rate reserve was enhanced during high-intensity exercise, without any significant change in peak oxygen uptake. Conclusions This specific warm-up enhanced heart rate reserve during a graded, symptom-limited exercise test on an ergocycle. Mechanisms more important than limited heart rate reserve are involved in the limitation of exercise tolerance in orthotopic heart transplant patients.

International audience; Studies using semantic priming paradigms to measure the integrity of the features underlying concepts in semantic dementia (SD) reported differential impairment, in that functional features appeared to be more robust to brain damage than other features, such as perceptual ones. However, these prior studies were single case reports and the inclusion of too many heterogeneous features under the "functional features" heading casts doubts on their apparent preservation. To verify the robustness of functional features compared with perceptual ones, we carried out a group study where we deliberately restricted the exploration of semantic features to two clearly defined types of attribute: visuoperceptual ("visual") versus contextual-functional ("contextual"). We administered an implicit lexical-decision priming task to 8 SD patients and 31 healthy matched controls, at baseline. Four of the patients underwent a follow-up assessment at one year. For controls, we found a significant priming effect in the visual condition, but not in the contextual one, whereas the SD group exhibited the reverse pattern of performances. The follow-up data provided evidence of the robustness of the dissociation between priming performances in the two attribute conditions. The fact that a particular priming effect was observed in the SD patients but not in controls could be regarded as a sign of semantic disequilibrium. Since perceptual features have been shown to be a core determinant of similarity-based/taxonomic relationships, whereas complementary-based/thematic processing relies mainly on contextual relationships, we interpreted our findings in terms of the differential recruitment of one of the two systems of semantic relationships (taxonomic vs. thematic). Moreover, these two distinct and parallel systems have previously been reported to coexist - and compete - in healthy adults. We thus argue that controls automatically drew on similarity-based/taxonomic relationships, leading to a significant priming effect for visual features but not for contextual ones. By contrast, their impaired perceptual features forced the SD patients to resort to the system of thematic relationships.

International audience; Proportional reasoning is very important logical skill required in mathematics and science problem solving as well as in everyday life decisions. However, there is a lack of studies on neurophysiological correlates of proportional reasoning. To explore the brain activity of healthy adults while performing a balance scale task, we used high-resolution EEG techniques and graph-theory based connectivity analysis. After unskilled subjects learned how to properly solve the task, their cortical power spectral density (PSD) maps revealed an increased parietal activity in the beta band. This indicated that subjects started to perform calculations. In addition, the number of inter-hemispheric connections decreased after learning, implying a rearrangement of the brain activity. Repeated performance of the task led to the PSD decrease in the beta and gamma bands among parietal and frontal regions along with a synchronization of lower frequencies. These findings suggest that repetition led to a more automatic task performance. Subjects were also divided in two groups according to their scores on the test of logical thinking (TOLT). Although no group differences in the accuracy and reaction times were found, EEG data showed higher activity in the beta and gamma bands for the group that scored better on TOLT. Learning and repetition induced changes in the pattern of functional connectivity were evident for all frequency bands. Overall, the results indicated that higher frequency oscillations in frontal and parietal regions are particularly important for proportional reasoning.

International audience; This study addresses the question of communication between medical wards and the nuclear medicine department for the realization of myocardial perfusion scintigraphy. It analyses the effects of a reminder for completing the content of an order form. It shows that the CDSS impacted ordering practices. It could be seen as a system enabling to structure the information and improve the quality of orders.

International audience; In two experiments, the authors explored whether there are any age differences associated with the ability to process outdated information during news reports comprehension. Younger and older participants (mean age: 70 years old) read passages in which a cause was first said to be responsible for the occurrence of a news event. New elements emerged from the investigation in progress and revealed that the original cause was incorrect. Inference response times indicated that older adults more than younger ones took advantage of an alternative cause mentioned in the text to put the outdated information in the background, whereas younger readers probably kept both causes activated. The research tested the concepts involved with age differences in updating situation model.

BackgroundTo investigate hedonic reactivity and the influence of unconscious emotional processes on the low sensitivity to positive reinforcement of food in anorexia nervosa (AN).MethodAN and healthy women were exposed to palatable food pictures just after a subliminal exposure to facial expressions (happy, disgust, fear and neutral faces), either while fasting or after a standardized meal (hungerversussatiety). Both implicit [facial electromyographic (EMG) activity from zygomatic and corrugator muscles, skin conductance, heart rate, and videotaped facial behavior] and explicit (self-reported pleasure and desire) measures of affective processes were recorded.ResultsIn contrast to healthy women, the AN patients did not display objective and subjective indices of pleasure to food pictures when they were in the hunger states. Pleasure to food cues (liking) was more affected than the desire to eat (wanting) in AN patients. Subliminal ‘fear faces’ increased corrugator muscle reactivity to food stimuli in fasting AN patients, as compared to controls.ConclusionsThe results suggest that unconscious fear cues increase the negative appraisal of alimentary stimuli in AN patients and thus contribute to decreased energy intake.

International audience; BACKGROUND: Previous findings revealed that the acquisition of new semantic concepts' labels was impaired in uncomplicated alcoholic patients. The use of errorless learning may therefore allow them to improve learning performance. However, the flexibility of the new knowledge and the memory processes involved in errorless learning remain unclear. METHOD: New concepts' labels acquisition was examined in 15 alcoholic patients and 15 control participants in an errorless learning condition compared with 19 alcoholic patients and 19 control subjects in a trial-and-error learning condition. The flexibility of the new information was evaluated using different photographs from those used in the learning sessions but representing the same concepts. All of the participants carried out an additional explicit memory task and an implicit memory task was also performed by subjects in the errorless learning condition. RESULTS: The alcoholic group in the errorless condition differed significantly from the alcoholic group in the trial-and-error condition but did not differ from the two control groups. There was no significant difference between results in the learning test and the flexibility task. Finally, in the alcoholic group, the naming score in the learning test was correlated with the explicit memory score but not with the implicit memory score. CONCLUSIONS: Using errorless learning, alcoholics improved their abilities to learn new concepts' labels. Moreover, new knowledge acquired with errorless learning was flexible. The errorless learning advantage may rely on explicit rather than implicit memory processes in these alcohol-dependent patients presenting only mild to moderate deficits of explicit memory capacities.

The human brain efficiently solves certain operations such as object recognition and categorization through a massively parallel network of dedicated processors. However, human cognition also relies on the ability to perform an arbitrarily large set of tasks by flexibly recombining different processors into a novel chain. This flexibility comes at the cost of a severe slowing down and a seriality of operations (100–500 ms per step). A limit on parallel processing is demonstrated in experimental setups such as the psychological refractory period (PRP) and the attentional blink (AB) in which the processing of an element either significantly delays (PRP) or impedes conscious access (AB) of a second, rapidly presented element. Here we present a spiking-neuron implementation of a cognitive architecture where a large number of local parallel processors assemble together to produce goal-driven behavior. The precise mapping of incoming sensory stimuli onto motor representations relies on a “router” network capable of flexibly interconnecting processors and rapidly changing its configuration from one task to another. Simulations show that, when presented with dual-task stimuli, the network exhibits parallel processing at peripheral sensory levels, a memory buffer capable of keeping the result of sensory processing on hold, and a slow serial performance at the router stage, resulting in a performance bottleneck. The network captures the detailed dynamics of human behavior during dual-task-performance, including both mean RTs and RT distributions, and establishes concrete predictions on neuronal dynamics during dual-task experiments in humans and non-human primates., Author Summary A ubiquitous aspect of brain function is its quasi-modular and massively parallel organization. The paradox is that this extraordinary parallel machine is incapable of performing a single large arithmetic calculation. How come it is so easy to recognize moving objects, but so difficult to multiply 357 times 289? And why, if we can simultaneously coordinate walking, group contours, segment surfaces, talk and listen to noisy speech, can we only make one decision at a time? Here we explored the emergence of serial processing in the primate brain. We developed a spiking-neuron implementation of a cognitive architecture in which the precise sensory-motor mapping relies on a network capable of flexibly interconnecting processors and rapidly changing its configuration from one task to another. Simulations show that, when presented with dual-task stimuli, the network exhibits parallel processing at peripheral sensory levels, a memory buffer capable of keeping the result of sensory processing on hold. However, control routing mechanisms result in serial performance at the router stage. Our results suggest that seriality in dual (or multiple) task performance results as a consequence of inhibition within the control networks needed for precise “routing” of information flow across a vast number of possible task configurations.

International audience; BACKGROUND: Previous findings revealed that the acquisition of new semantic concepts' labels was impaired in uncomplicated alcoholic patients. The use of errorless learning may therefore allow them to improve learning performance. However, the flexibility of the new knowledge and the memory processes involved in errorless learning remain unclear. METHOD: New concepts' labels acquisition was examined in 15 alcoholic patients and 15 control participants in an errorless learning condition compared with 19 alcoholic patients and 19 control subjects in a trial-and-error learning condition. The flexibility of the new information was evaluated using different photographs from those used in the learning sessions but representing the same concepts. All of the participants carried out an additional explicit memory task and an implicit memory task was also performed by subjects in the errorless learning condition. RESULTS: The alcoholic group in the errorless condition differed significantly from the alcoholic group in the trial-and-error condition but did not differ from the two control groups. There was no significant difference between results in the learning test and the flexibility task. Finally, in the alcoholic group, the naming score in the learning test was correlated with the explicit memory score but not with the implicit memory score. CONCLUSIONS: Using errorless learning, alcoholics improved their abilities to learn new concepts' labels. Moreover, new knowledge acquired with errorless learning was flexible. The errorless learning advantage may rely on explicit rather than implicit memory processes in these alcohol-dependent patients presenting only mild to moderate deficits of explicit memory capacities.

International audience; In three experiments, we examined lexical competition effects using the phonological priming paradigm in a shadowing task. Experiments 1A and 1B showed that an inhibitory priming effect occurred when the primes mismatched the targets on the last phoneme (/bagar/-/bagaj/). In contrast, a facilitatory priming effect was observed when the primes mismatched the targets on the medial phoneme (/viraj/-/vilaj/). Experiment 2 replicated these findings with primes presented visually rather than auditorily. The data thus indicate that the position of the mismatching phoneme is a critical factor in determining the competition effect between prime and target words.

International audience; OBJECTIVE: We combined event-related potential (ERP) and magnetoencephalography (MEG) acquisition and analysis to investigate the electrophysiological markers of the inhibitory processes involved in the number/length interference in a Piaget-like numerical task. METHODS: Eleven healthy subjects performed four gradually interfering conditions with the heuristic "length equals number" to be inhibited. Low resolution tomography reconstruction was performed on the combined grand averaged electromagnetic data at the early (N1, P1) and late (P2, N2, P3(early) and P3(late)) latencies. Every condition was analyzed at both scalp and regional brain levels. RESULTS: The inhibitory processes were visible on the late components of the electromagnetic brain activity. A right P2-related frontal orbital activation reflected the change of strategy in the inhibitory processes. N2-related SMA/cingulate activation revealed the first occurrence of the stimuli processing to be inhibited. Both P3 components revealed the working memory processes operating in a medial temporal complex and the mental imagery processes subtended by the precuneus. CONCLUSIONS: Simultaneous ERP and MEG signal acquisition and analysis allowed to describe the spatiotemporal patterns of neural networks involved in the inhibition of the "length equals number" interference. SIGNIFICANCE: Combining ERP and MEG ensured a sensitivity which could be reached previously only through invasive intracortical recordings.

International audience; Cognitive procedural learning is characterised by three phases, each involving distinct processes. Considering the implication of episodic memory in the first cognitive stage, the impairment of this memory system might be responsible for a slowing down of the cognitive procedural learning dynamics in the course of ageing. Performances of massed cognitive procedural learning were evaluated in older and younger participants using the Tower of Toronto task. Nonverbal intelligence and psychomotor abilities were used to analyse procedural dynamics, while episodic memory and working memory were assessed to measure their respective contributions to learning strategies. This experiment showed that older participants did not spontaneously invoke episodic memory and presented a slowdown in the cognitive procedural learning associated with a late involvement of working memory. These findings suggest that the slowdown in the cognitive procedural learning may be linked with the implementation of different learning strategies less involving episodic memory in older participants.

International audience; This behavioral study aimed at assessing the effect of two variables on the degree of hemispheric specialization for language. One of them was the grapho-phonemic translation (transformation) (letter-sound mapping) and the other was the participants'gender. The experiment was conducted with healthy volunteers. A divided visual field procedure has been used to perform a phoneme detection task implying either regular (transparent) grapho-phonemic translation (letter-sound mapping consistency) or irregular (non-transparent) grapho-phonemic translation (letter-sound mapping inconsistency). Our results reveal a significant effect of grapho-phonemic translation on the degree of hemispheric dominance for language. The phoneme detection on items with transparent translation (TT) was performed faster than phoneme detection on items with non-transparent translation (NTT). This effect seems to be due to faster identification of TT than NTT when the items were presented in the left visual field (LVF)-right hemisphere (RH). There was no difference between TT and NTT for stimuli presented in the right visual field (RVF)-left hemisphere (LH). This result suggests that grapho-phonemic translation or the degree of transparency can affect the degree of hemispheric specialization, by modulating the right hemisphere activity. With respect to gender, male participants were significantly more lateralized than female participants but no interaction was observed between gender and degree of transparency.

Background and Purpose— To analyze the postural behavior of standing stroke patients: (1) To differentiate between postural impairment attributable to the neurological condition (deficits attributable to the cerebral lesion) and postural impairment attributable to new mechanical constraints caused by body weight asymmetry; (2) To assess the involvement of each limb in the postural impairment; (3) To better understand which clinical deficits underlie the postural impairment. Methods— The posturographic characteristics of each limb in 41 stroke patients (first hemispheric stroke: 16 left, 25 right cerebral lesions) required to stand in their preferred posture were compared to those in 40 matched healthy individuals required to stand asymmetrically. Results— Compared to normal individuals in a similar asymmetrical posture, stroke patients were more unstable. The weight bearing asymmetry and the lateral postural instability were mainly related to spatial neglect. The paretic limb was unable to bring into play a normal longitudinal pattern of the center of pressure, which reflects an impaired stabilization control. Overall postural instability occurred when the strong limb was unable to compensate for the postural impairment of the paretic limb. Conclusions— The weight bearing asymmetry of standing stroke patients is not the primary cause of their postural imbalance, which is rather the consequence of impaired control of postural stabilization involving both limbs. Weight bearing asymmetry may not be the principle target of rehabilitation programs aiming at restoring standing balance after stroke. Instead it is suggested that more account should be taken of the compensatory role of the strong limb.

Identifying the sequence of computations which constitute a cognitive task is a fundamental problem in neuroscience. Here we show, using functional magnetic resonance imaging (fMRI), that we can parse, at the time scale of about 100 ms, the different stages of brain activations which compose a complex sequential task. To identify timing information from the slow blood oxygen level-dependent (BOLD) signal response, we use a simple analytic method, based on periodic stimulation and an analysis of covariation of the spectral parameters (phase and power spectrum at the stimulation frequency) with the different experimental conditions. We implement this strategy in a sequential task, where the onset and duration of different stages are under experimental control. We are able to detect changes in onset latency and in the duration of the response, in an invariant fashion across different brain regions, and reconstruct the stream of activations consistent with five distinct stages of processing of the task. Sensory and motor clusters activate in the expected order and for the expected duration. The timing of sensory activations is more precise than the timing of motor activation. We also parse in time the reading-verbal network: visual extrastriate and phonological access regions (supramarginal gyrus) activate at the time of word presentation, while the inferior frontal gyrus, the anterior cingulate and the supplementary motor area are activated during the rehearsal period. © 2006 Elsevier Inc. All rights reserved. Fil: Sigman, Mariano. Inserm; Francia. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Jobert, A.. Inserm; Francia Fil: LeBihan, D.. Inserm; Francia Fil: Dehaene, Stanislas. Inserm; Francia

International audience; Sleepiness is considered to be the major cause of increased traffic accidents in patients with obstructive sleep apnoea syndrome (OSAS). Until now, OSAS patients' driving ability has been assessed using driving simulators, but no assessment in a more natural driving environment has been carried out to date. The aim of the present study was to evaluate driving parameters in OSAS and in controls on a road safety platform, and to compare them with attentional in-laboratory measures before and after continuous positive airway pressure treatment. The parameters measured were: reaction time; distance to stop and number of collisions on the platform; maintenance of wakefulness; and sustained, selective and divided attention in laboratory. Patients exhibited much longer reaction times than controls, leading to a lengthening of the vehicle's stopping distance of 8.8 m at 40 km.h(-1) and to twice the number of collisions. Patients did not demonstrate objective sleepiness or selective and sustained attention deficits. Divided attention deficits were found. However, they did not allow the prediction of real driving impairment. After CPAP treatment, there was no longer any difference between patients and controls regarding driving and attention performances. Driving abilities are significantly impaired in obstructive sleep apnoea syndrome. After continuous positive airway pressure treatment, deficits were normalised. This stresses the importance of evaluating attentional parameters in apnoeic patients and of offering continuous positive airway pressure treatment even to non-sleepy subjects.

The anterior cingulate cortex (ACC) is known to play a crucial role in the fast adaptations of behavior based on immediate reward values. What is less certain is whether the ACC is also involved in long-term adaptations to situations with uncertain outcomes. To study this issue, we placed macaque monkeys in a probabilistic context in which the appropriate strategy to maximize reward was to identify the stimulus with the highest reward value (optimal stimulus). Only knowledge of the theoretical average reward value associated with this stimulus--referred to as 'the task value'--was available. Remarkably, in each trial, ACC pre-reward activity correlated with the task value. Importantly, this neuronal activity was observed prior to the discovery of the optimal stimulus. We hypothesize that the received rewards and the task value, constructed a priori through learning, are used to guide behavior and identify the optimal stimulus. We tested this hypothesis by muscimol deactivation of the ACC. As predicted, this inactivation impaired the search for the optimal stimulus. We propose that ACC participates in long-term adaptation of voluntary reward-based behaviors by encoding general task values and received rewards.

International audience; Why is the human brain fundamentally limited when attempting to execute two tasks at the same time or in close succession? Two classical paradigms, psychological refractory period (PRP) and task switching, have independently approached this issue, making significant advances in our understanding of the architecture of cognition. Yet, there is an apparent contradiction between the conclusions derived from these two paradigms. The PRP paradigm, on the one hand, suggests that the simultaneous execution of two tasks is limited solely by a passive structural bottleneck in which the tasks are executed on a first-come, first-served basis. The task-switching paradigm, on the other hand, argues that switching back and forth between task configurations must be actively controlled by a central executive system (the system controlling voluntary, planned, and flexible action). Here we have explicitly designed an experiment mixing the essential ingredients of both paradigms: task uncertainty and task simultaneity. In addition to a central bottleneck, we obtain evidence for active processes of task setting (planning of the appropriate sequence of actions) and task disengaging (suppression of the plan set for the first task in order to proceed with the next one). Our results clarify the chronometric relations between these central components of dual-task processing, and in particular whether they operate serially or in parallel. On this basis, we propose a hierarchical model of cognitive architecture that provides a synthesis of task-switching and PRP paradigms.

International audience; The purpose of this experiment was to determine whether a faded knowledge of results (KR) frequency during observation of a model's performance enhanced error detection capabilities. During the observation phase, participants observed a model performing a timing task and received KR about the model's performance on each trial or on one of two trials. Delayed retention and transfer tests were used to assess the observer's ability to detect error in the model's performance and in the participant's performance while physically practicing the task. Results indicated a beneficial effect of a reduced KR frequency for performance stability and the ability to detect errors in both the model and the participant's own performance. The results suggest that aspects of the processing mechanism(s) developed in observational learning and related to KR are probably similar to those developed through physical practice.

International audience; We used behavioral and functional magnetic resonance imaging (fMRI) methods to probe the cerebral organization of a simple logical deduction process. Subjects were engaged in a motor trial-and-error learning task, in which they had to infer the identity of an unknown 4-key code. The design of the task allowed subjects to base their inferences not only on the feedback they received but also on the internal deductions that it afforded (autoevaluation). fMRI analysis revealed a large bilateral parietal, prefrontal, cingulate, and striatal network that activated suddenly during search periods and collapsed during ensuing periods of sequence repetition. Fine-grained analyses of the temporal dynamics of this search network indicated that it operates according to near-optimal rules that include 1) computation of the difference between expected and obtained rewards and 2) anticipatory deductions that predate the actual reception of positive reward. In summary, the dynamics of effortful mental deduction can be tracked with fMRI and relate to a distributed network engaging prefrontal cortex and its interconnected cortical and subcortical regions.

The aim of this study was to carry out a statistical analysis of the Banister model to verify how useful it is in monitoring the training programmes of elite swimmers. The accuracy, the ill-conditioning and the stability of this model were thus investigated. The training loads of nine elite swimmers, measured over one season, were related to performances with the Banister model. First, to assess accuracy, the 95% bootstrap confidence interval (95% CI) of parameter estimates and modelled performances were calculated. Second, to study ill-conditioning, the correlation matrix of parameter estimates was computed. Finally, to analyse stability, iterative computation was performed with the same data but minus one performance, chosen at random. Performances were related to training loads for all participants (R(2) = 0.79 +/- 0.13, P < 0.05) and the estimation procedure seemed to be stable. Nevertheless, the range of 95% CI values of the most useful parameters for monitoring training was wide: t(a) = 38 (17, 59), t(f) = 19 (6, 32), t(n) = 19 (7, 35), t(g) = 43 (25, 61). Furthermore, some parameters were highly correlated, making their interpretation worthless. We suggest possible ways to deal with these problems and review alternative methods to model the training-performance relationships.

Objective: The first aim of this study was to determine whether ordinary postural clinical performance varied with an additional cognitive task. The second purpose was to valid the predictive value for falling of two clinical tests. Methodology: The sample comprised ninety-five women with osteoporosis who lived independently in the community and aged over 70 years (mean 73.4 ± 1.7 years). Timed “Up & Go” test (TUG) and One leg balance (OLB) were realised. Tests were randomly assigned. Trials were realised with or without a cognitive additional task (math task involving subtraction by twos or fives or addition by threes). Results: For both tests (TUG and OLB), performance decreased in the dual-tasks condition (p

Background The kinetics and kinematics of the glenohumeral joints, and shoulder muscles activities during the initial phase of learning wheelchair propulsion by individuals with paraplegia have been partially described. But no studies carry out the kinematics of the upper-limb during the learning of non-constrained open field locomotion with a wheelchair. Methods Ten subjects with no manual wheelchair experience propelled themselves repetitively straight ahead along an 11 m linear path. Upper-limb segment orientations were measured with an electromagnetic system. Angular displacements of joints were determined using a standardized protocol [Wu, G., Van der Helm, F.C.T., Veeger, H.E.J., Makhsous, M., Van Roy, P., Anglin, C., Nagels, J., Karduna, A.R., McQuade, K., Wang, X., Wernerl, F.W., Buchholzm, B., 2005. ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion—Part II: shoulder, elbow, wrist and hand. J. Biomech. 38(5), 981–992] and a modeling method [Biryukova, E.V., Roby-Brami, A., Frolov, A.A., Mokhtari, M., 2000. Kinematics of human arm reconstructed from spatial tracking system recordings. J. Biomech. 33, 985–995]. Findings A full 3-D scapular motion description was obtained that allowed us to measure the mean amplitudes of rotation for the nine degrees of freedom of our model. The change in the propulsion pace and the repetition of trials induced a general increase of amplitudes of joint rotations that can explain the increase of velocity among trials. Interpretation We did not observe a freezing of any DOF as predicted by Bernstein’s theory of motor learning, but the increase in joint movement amplitudes could correspond to his “unfreezing of DOF” stage. This non-respect of Bernstein’s theory could originate in the relative simplicity of the task.

We investigated the effect of performing a mental arithmetic task with two levels of difficulty on the regulation of centre of foot pressure (COP) displacements during bipedal quiet standing in young healthy individuals. There was also a control condition in which no concurrent task was required. A space-time-domain analysis showed decreased COP displacements, along the antero-posterior axis, when participants concurrently performed the most difficult mental arithmetic task. Frequency-domain and stabilogram-diffusion analyses further suggested these decreased COP displacements to be associated with an increased stiffness and a reduction of the exploratory behaviours in the short term, respectively.

International audience; This study aimed at supporting the specificity of learning hypothesis, when aiming was based on internal cues, as directing the hand toward a "self-defined" target location. Participants practiced modest (20 trials) or intensive (720 trials) training with visual and proprioceptive information or proprioceptive information only. Pretests and posttests were performed in sensory conditions that did or did not match the training condition. Results showed that dynamic visual cues played a dominant role at the beginning of the task, and an intensive practice resulted in increased accuracy of kinesthetic information and efferent mechanisms of motor responses. These results have implications with regard to motor learning conceptions and training as a function of the task constraints.

To help people with visual impairment, especially people with severely impaired vision, access graphic information on a computer screen, we have carried out fundamental research on the effect of increasing the number of detection fields. In general, application of the parallelism concept enables information to be accessed more precisely and easily when the number of sensors is high. We have developed a "Braille Box" by modifying Braille cells to form a tactile stimulator array which is compatible with the fingertip. Each pin can be controlled independently so that we can change the size and type of array in order to study the tactile perception of both simple and complex graphical forms. Our results show that by applying the parallelism concept to the detection field, people with visual impairment can increase the speed of exploration of geometric forms without decreasing the level of accuracy: thus, avoiding a speed-accuracy tradeoff. Further experiments need to be done with this Braille Box in order to improve the device and help people with visual impairment access graphic information.

International audience; The purpose of this study is to determine if increasing the potential risk of slipping on support surface materials decreases postural dynamics and task performance. Seated subjects were asked to exert maximum horizontal two-handed isometric pushes as quickly as possible on a dynamometric bar. Reaction forces exerted at seat (Rxs and Rzs) and footrest (Rxf and Rzf) were measured using force sensors. A dynamometric bar measured horizontal push force (Fx). Global adherence ratio (micro) was calculated. Three support surface materials, characterised by different coefficients of friction, were tested. The same surfaces were placed on the seat and the footrest during a series of pushes. It was shown that the different support surfaces significantly influence Fx, Rxs, Rzs, Rzf and micro maximum values obtained at the end of the push. Even when the instructions given to the subject are to produce a maximum push, the maximum horizontal force applied to the bar differs according to the support surface material. Dynamic postural adjustments are influenced by characteristics of slipperiness of support surfaces. The coefficient of friction contributes an essential element to the program of postural dynamics, which in turn modulates the task performance. During brief isometric pushes, seated subjects have the capacity to control the potential risk of slipping.

The training-performance relationship is particularly important for elite sports coaches who search for reproducible phenomena useful for organizing the athlete’s training program. Many authors have studied the relative influence of training (7, 22, 23, 27) and found that reactions to training depend on volume, intensity and frequency of the training sessions (7, 16, 23). Others have reported divergent results (4, 9), perhaps related to the fact that delayed effects and inter–individual differences were not taken into account. For individual swimmers, mathematical models have been developed to describe the dynamic aspect of training and the consequences of succession of training loads over time (2). The Banister model (2, 3, 4) and its modifications (5, 6) are based on two antagonistic functions, both calculated from the training impulse. Studies on cellular adaptability reactions to exercise (3) have demonstrated that the negative function can be assimilated to a fatiguing impulse. The positive function can be compared to a fitness impulse resulting from the organism’s adaptation to training. Expressed as an exponential, the functions account for the decreasing impact of the training effect. When iterative training sessions are considered, the time course of performance is described by: pt=p0+ka∑s=0t-1e-(t-s)/τaws-kf∑s=0t-1e-(t-s)/τfws where pt is the known performance at week (or day) t; ws is the known training load per week (or day) from the first week of training to the week (or day) preceding performance pt; ka, kf are the fitness and fatigue multiplying factors, respectively; τa, τf are the fitness and fatigue decay time constants, respectively; p0 corresponds to an initial basic level of performance. There is no clear consensus on just how many data points are needed per parameter to ensure a stable solution in a regression analysis. Proposals reported in the literature have ranged from 5 to 50. Stevens (26) recommends a nominal number of 15 observations per parameter (except the intercept parameter) for a multiple linear regression. But since the Banister model is a non-linear model, inference is based on asymptotic theory (10), which implies more data points per parameter than for a linear regression model. This means a large number of observations would be required to obtain precise results and enable pertinent statistical analysis. The Banister model also assumes the parameters remain constant over time, an assumption which is not consistent with observed time-dependent alterations in response to training (3, 4, 6, 22). When few repeated measurements are available for several subjects, mixed models provide an attractive solution (29). Instead of constructing a personal model for each subject, a model of popular behavior is constructed, allowing parameters to vary from one individual to another, to take into account the heterogeneity between subjects. Particular care in characterizing random variation in the data is required to recognize two levels of variability: random variation among measurements within a given individual (intra-individual variation) and random variation among individuals (inter-individual variation) (10). In addition, mixed models analyze responses corresponding to different dose inputs (10), a common situation in swimming since training loads differ with age, specialty, and/or competition level (7, 23). The aim of the present study was to investigate the effect of training on performance of 13 elite swimmers taking into account A) individual profiles; B) sub population profiles; and C) time effect over 3 seasons.

International audience; Paradigms of Latent Inhibition (LI) are inter-species and derived from learning theories. They are considered as tools which allow the attentional processes to be studied. The absence of LI is interpreted as difficulty in discriminating relevant and irrelevant stimuli. Abolition of LI has been shown in acute schizophrenics. The objectives of our study were partly to validate an LI paradigm, based on a contingency detection between two stimuli, in healthy subjects, and partly to analyse LI in schizophrenics. The study included 105 subjects (65 patients and 40 controls). Patients fulfilled the DSM IV diagnosis of schizophrenia. 35 in the acute phase and 30 in the chronic phase. We observed a loss of LI for acute schizophrenics, and an enhancement of LI for chronic schizophrenics. The variations in LI are interpreted from the perspective of a disturbance in the attentional processes. The LI status in acute schizophrenics appears to correlate with the clinical criteria with a prognostic value (low intensity of the negative dimension, late age at the first hospitalization). Moreover, the enhancement of LI correlates with the negative dimension of schizophrenic disease. This correlation is found in acute and chronic schizophrenics. It suggests that the variations of LI may be an indicator of adaptive strategies to a cognitive dysfunction specific to schizophrenia.

International audience; BACKGROUND: The objective of this study was to analyze the sensory and cognitive functions associated with activated brain regions characterizing mental strategy relative to degree of expertise in aviation-related tasks. METHODS: We used echo-planar functional magnetic resonance imaging (fMRI) technique to examine brain activity in expert pilots (n = 6) compared with novice pilots (n = 6) during performance of a simulated aviation track-following task at 200 knots vs. 100 knots. RESULTS: Expert pilots showed reduced activity in visual and motor regions that contrasted with predominant activation within anterior structures including the frontal and prefrontal cortices; structures involved in visual working memory, planning, selective attention and decision making functions. Novice pilots showed widespread activation of anterior and posterior brain structures, with a rise in activity in the visual, parietal and motor cortices as task difficulty increased. CONCLUSIONS: A high level of performance in the track-following task related to a high degree of expertise in the aviation field. This corresponded to experts performing perceptual and mnemonic processing through a network of specialized functions from visual through multiple prefrontal areas. By contrast, the novice pilots predominantly show activity associated with non-specific perceptual processing and without subsequent representation of selective information in working memory.

International audience; Depression appears to interfere more with effortful processes than with automatic processes. This study aimed to examine attentional resources allocation by means of RT on effortful detection tasks. Ten depressed inpatients during illness and at recovery and ten healthy control subjects were given simple and choice reaction time tasks. Two types of effort demanding conditions were assessed (1) the combination of two concurrent tasks and (2) tasks involving decision making. Depressed patients improved from single to dual tasks whereas recovered and control worsened. Depressed patients showed a significant time and accuracy impairment when decision processes were involved. The decision making impairment co-occurred with a deficit in the orientation of the attention. The decline with decision making was not worsened when the choice task combined with a concurrent task and was reversible with recovery. This pattern of results exhibits differential sensitivity between two effortful tasks. Depressives may be able to mobilize resources to complete effortful tasks as far as decision processing is not required.

International audience; We tested whether lorazepam (a benzodiazepine) affects perceptual processes involved in the computation of contour information. Subjects matched incomplete forms whose contour was composed of line segments varying in their spacing and in their alignment. An initial centrally displayed object (a reference) was followed by two laterally displayed pictures, a target and a distractor. The distractor was the mirror-reversed version of the target. In one condition, the reference was always an outline drawing of an object. In another condition, the reference was either an outline drawing or an incomplete form. All subjects were run in both conditions. Lorazepam 0.038 mg/kg induced a larger increase in RTs than the placebo and lorazepam 0.026 mg/kg when the spacing between local contour elements was larger than 10.8' arc and when the line segments were not aligned. Performance was improved in the 0.038 mg/kg lorazepam group when subjects started with the condition in which the reference was always an outline drawing. Performance was not correlated with sedation. These results show that lorazepam impairs visual perception. They are interpreted in terms of impaired binding processes, which can be compensated for by the use of stored object representations. This effect is consistent with electrophysiological studies showing that the neuromediator GABA is involved in perceptual processes.

International audience; Whether Ss can attend to physical dimensions of objects without access to semantic information about them was examined. Ss decided which of 2 laterally presented pictures, a target and a distractor, had the same orientation (Experiment 1), size (Experiment 2), luminance (Experiment 3), or color (Experiment 4) as a reference picture. In each experiment, the matching stimuli were either physically identical, semantically related, or semantically unrelated. The reference stimulus and the distractor were either semantically related or unrelated. When matching was based on orientation or on size, performance was facilitated when the matching stimuli were semantically related, and it was disrupted when the distractor was semantically related to the reference stimulus. Semantic effects were eliminated when matching was based on luminance or color. The results are discussed in terms of physiological data, form and surface information, and global and local processing.

International audience; The growth law for the development of top athletes performances remains unknown in quantifiable sport events. Here we present a growth model for 41351 best performers from 70 track and field (T&F) and swimming events and detail their characteristics over the modern Olympic era. We show that 64% of T&F events no longer improved since 1993, while 47% of swimming events stagnated after 1990, prior to a second progression step starting in 2000. Since then, 100% of swimming events continued to progress.We also provide a measurement of the atypicity for the 3919 best performances (BP) of each year in every event. The secular evolution of this parameter for T&F reveals four peaks; the most recent (1988) followed by a major stagnation. This last peak may correspond to the most recent successful attempt to push forward human physiological limits. No atypicity trend is detected in swimming. The upcoming rarefaction of new records in sport may be delayed by technological innovations, themselves depending upon economical constraints.

FORESTIER, N., N. TEASDALE, and V. NOUGIER. Alteration of the position sense at the ankle induced by muscular fatigue in humans. Med. Sci. Sports Exerc., Vol. 34, No. 1, 2002, pp. 117–122. Purpose: The purpose of this study was to investigate how an isometric exhaustion test affects the position sense at the ankle using an active matching task. Methods: Eight male subjects with a mean age 24.6 yr participated in the study. Subjects’ ability to match the right ankle with the position of the left reference ankle position— determined using signed and absolute errors and variability—was investigated. This task was realized for four ankle angular values (in degrees), two in dorsiflexion (P -20 ,P -10) and two in plantarflexion (P20 ,P 10) and for two experimental conditions: 1) normal and 2) fatigue. Muscular fatigue was induced in tibialis anterior (TA) of the right leg (ankle dorsiflexor) by using an isometric test. Subjects were instructed to maintain a workload of 70% of their maximal voluntary contraction in series of 40 s. Results: With fatigue, subjects produced ankle movements characterized by greater absolute errors for movements of large amplitude in dorsiflexion and for movements of small amplitude in plantarflexion. In addition, using a “worst-case scenario” analysis, results showed that errors were significantly greater than the normal functioning range for 20° dorsiflexion and 10° plantarflexion positioning. Conclusions: The acuity of the position sense at the ankle is reduced subsequent to a fatigue protocol. The influence and the potential deleterious effects of