"mind the gap": The size-distance dissociation in visual neglect is a cueing effect

There is a growing body of evidence that the processes mediating the allocation of spatial attention within objects may be separable from those governing attentional distribution between objects. In the neglect literature, a related proposal has been made regarding the perception of (within-object) sizes and (between-object) distances. This proposal follows observations that, in size-matching and bisection tasks, neglect is more strongly expressed when patients are required to attend to the sizes of discrete objects than to the (unfilled) distances between objects. These findings are consistent with a partial dissociation between size and distance processing, but a simpler alternative must also be considered. Whilst a neglect patient may fail to explore the full extent of a solid stimulus, the estimation of an unfilled distance requires that both endpoints be inspected before the task can be attempted at all. The attentional cueing implicit in distance estimation tasks might thus account for their superior performance by neglect patients. We report two bisection studies that address this issue. The first confirmed, amongst patients with left visual neglect, a reliable reduction of rightward error for unfilled gap stimuli as compared with solid lines. The second study assessed the cause of this reduction, deconfounding the effects of stimulus type (lines vs. gaps) and attentional cueing, by applying an explicit cueing manipulation to line and gap bisection tasks. Under these matched cueing conditions, all patients performed similarly on line and gap bisection tasks, suggesting that the reduction of neglect typically observed for gap stimuli may be attributable entirely to cueing effects. We found no evidence that a spatial extent, once fully attended, is judged any differently according to whether it is filled or unfilled.

A spatial explanation for synchrony biases in perceptual grouping: Consequences for the temporal-binding hypothesis

If two images are shown in rapid sequential order, they are perceived as a single, fused image. Despite this, recent studies have revealed that fundamental perceptual processes are influenced by extremely brief temporal offsets in stimulus presentation. Some researchers have suggested that this is due to the action of a cortical temporal-binding mechanism, which would serve to keep multiple mental representations of one object distinct from those of other objects. There is now gathering evidence that these studies should be reassessed. This article describes evidence for sensitivity to fixational eye and head movements, which provides a purely spatial explanation for the earlier results. Taken in conjunction with other studies, the work serves to undermine the current body of behavioral evidence for a temporal-binding mechanism.

RECHERCHE TRANSLATIONNELLE EN NEUROSCIENCES PSYCHIATRIQUES: DE L'ANIMAL MODELE DE SCHIZOPHRENIE A LA DETECTION D'UNE DESORIENTATION SPATIALE, PRATIQUE OU SYMBOLIQUE CHEZ DES PATIENTS

La modélisation, chez l'animal, de maladies psychiatriques telles que la schizophrénie repose sur différentes démarches visant à induire des perturbations cérébrales similaires à celles observées dans la maladie. Nous avons cherché à étudier chez le rat les effets d'une diminution (50%) transitoire en glutathion (GSH) durant le développement (PND 5 à PND 16) à partir de l'implication, chez des adultes, des conséquences de cette perturbation dans des mécanismes fondamentaux de traitement de l'information sensorielle. Cette thèse évalue et documente les déficits de compétences de navigation spatiale dans ce modèle. Nous avons mis en évidence des effets comportementaux à partir de l'identification de différences particulières dans des tâches d'orientation: des difficultés, chez les rats ayant subi un déficit en GSH, à élaborer une représentation globale de l'environnement dans lequel ils se déplacent, difficultés compensées par une attention particulière aux détails visuels le composant. Cette stratégie réactive compensatoire est efficace lorsque les conditions permettent un ajustement continu aux repères visuels environnementaux. Elle ne permet cependant pas des prédictions et des attentes sur ce qui devrait être rencontré et perçu dans une certaine direction, dès qu'une partie des informations visuelles familières disparaît. Il faudrait pour cela une capacité fondée sur une représentation abstraite, à distance des modalités sensorielles qui en ont permis son élaboration. Notre thèse soutient que les déficits, supposés participer à l'émergence de certains symptômes de la maladie, auraient également des conséquences sur l'élaboration de la représentation spatiale nécessaire à des capacités d'orientation effectives et symboliques. - The study of a psychiatric disease such as schizophrenia in an animal model relies on different approaches attempting to replicate brain perturbations similar to those observed in the illness. In the present work, behavioural consequences of a functional deficit in brain connectivity and coordination were assessed in rats with a transitory glutathione (GSH) deficit induced during the postnatal development (PND 5-PND 16) with daily injections of BSO (1- buthionine-(S,R)- sulfoximine). We searched for a theoretical syndrome associating ecologically relevant behavioural adaptive deficits and resulting from the weakening of sensory integration processes. Our results revealed significant and specific deficit of BSO treated rats in spatial orientation tasks designed to test for cognitive mapping abilities. Treated rats behaved as if impaired in the proactive strategies supported by an abstract representation such as a cognitive map. In contrast their performances were preserved whenever the environmental conditions allowed for adaptative reactive strategies, an equivalent of the visual affordances described by Gibson (1958). This supports our thesis that BSO treated rats expressed difficulties in elaborating a global representation of the environment. This deficit was completely - or - partially compensated by the development of an increased attention to the environment's visual details. This compensatory reactive strategy requires a rich environment allowing for continuous adjustment to visual cues. However, such adjustment doesn't allow to predictions and expectancies about what should be met and perceived in a certain direction, when familiar visual spatial cues are missing. Such competencies require orientation based on the use of an abstract spatial representation, independent from the specific sensory modalities that have participated to its elaboration. The impairment of BSO rats such spatial representation could result from a deficit in the integration and organization of perceptual information. Our model leads to the hypothesis that these fundamental deficits might account for certain symptoms of schizophrenia. They would also interfere with in the capacity to elaborate spatial representation necessary for optimal orientation in natural, artificial or symbolic environment.

Interhemispheric coupling between the posterior sylvian regions impacts successful auditory temporal order judgment.

Accurate perception of the temporal order of sensory events is a prerequisite in numerous functions ranging from language comprehension to motor coordination. We investigated the spatio-temporal brain dynamics of auditory temporal order judgment (aTOJ) using electrical neuroimaging analyses of auditory evoked potentials (AEPs) recorded while participants completed a near-threshold task requiring spatial discrimination of left-right and right-left sound sequences. AEPs to sound pairs modulated topographically as a function of aTOJ accuracy over the 39-77ms post-stimulus period, indicating the engagement of distinct configurations of brain networks during early auditory processing stages. Source estimations revealed that accurate and inaccurate performance were linked to bilateral posterior sylvian regions activity (PSR). However, activity within left, but not right, PSR predicted behavioral performance suggesting that left PSR activity during early encoding phases of pairs of auditory spatial stimuli appears critical for the perception of their order of occurrence. Correlation analyses of source estimations further revealed that activity between left and right PSR was significantly correlated in the inaccurate but not accurate condition, indicating that aTOJ accuracy depends on the functional decoupling between homotopic PSR areas. These results support a model of temporal order processing wherein behaviorally relevant temporal information--i.e. a temporal 'stamp'--is extracted within the early stages of cortical processes within left PSR but critically modulated by inputs from right PSR. We discuss our results with regard to current models of temporal of temporal order processing, namely gating and latency mechanisms.

Working memory load improves early stages of independent visual processing.

Increasing evidence suggests that working memory and perceptual processes are dynamically interrelated due to modulating activity in overlapping brain networks. However, the direct influence of working memory on the spatio-temporal brain dynamics of behaviorally relevant intervening information remains unclear. To investigate this issue, subjects performed a visual proximity grid perception task under three different visual-spatial working memory (VSWM) load conditions. VSWM load was manipulated by asking subjects to memorize the spatial locations of 6 or 3 disks. The grid was always presented between the encoding and recognition of the disk pattern. As a baseline condition, grid stimuli were presented without a VSWM context. VSWM load altered both perceptual performance and neural networks active during intervening grid encoding. Participants performed faster and more accurately on a challenging perceptual task under high VSWM load as compared to the low load and the baseline condition. Visual evoked potential (VEP) analyses identified changes in the configuration of the underlying sources in one particular period occurring 160-190 ms post-stimulus onset. Source analyses further showed an occipito-parietal down-regulation concurrent to the increased involvement of temporal and frontal resources in the high VSWM context. Together, these data suggest that cognitive control mechanisms supporting working memory may selectively enhance concurrent visual processing related to an independent goal. More broadly, our findings are in line with theoretical models implicating the engagement of frontal regions in synchronizing and optimizing mnemonic and perceptual resources towards multiple goals.

Neuropsychological dysfunction related to earlier occupational exposure to mercury vapor

We assessed the neuropsychological test performances of 26 patients (mean age = 41.5 ± 6.1 years; mean years of education = 9.8 ± 1.8; 20 males) diagnosed with chronic occupational mercurialism who were former workers at a fluorescent lamp factory. They had been exposed to elemental mercury for an average of 10.2 ± 3.8 years and had been away from this work for 6 ± 4.7 years. Mean urinary mercury concentrations 1 year after cessation of work were 1.8 ± 0.9 µg/g creatinine. Twenty control subjects matched for age, gender, and education (18 males) were used for comparison. Neuropsychological assessment included attention, inhibitory control, verbal and visual memory, verbal fluency, manual dexterity, visual-spatial function, executive function, and semantic knowledge tests. The Beck Depression Inventory and the State and Trait Inventory were used to assess depression and anxiety symptoms, respectively. The raw score for the group exposed to mercury indicated slower information processing speed, inferior performance in psychomotor speed, verbal spontaneous recall memory, and manual dexterity of the dominant hand and non-dominant hand (P < 0.05). In addition, the patients showed increased depression and anxiety symptoms (P < 0.001). A statistically significant correlation (Pearson) was demonstrable between mean urinary mercury and anxiety trait (r = 0.75, P = 0.03). The neuropsychological performances of the former workers suggest that occupational exposure to elemental mercury has long-term effects on information processing and psychomotor function, with increased depression and anxiety also possibly reflecting the psychosocial context.

Facteurs influencing haptic shape perception

Le but de cette étude était de déterminer la contribution de plusieurs facteurs (le design de la tâche, l’orientation d’angle, la position de la tête et du regard) sur la capacité des sujets à percevoir les différences de formes bidimensionnelles (2-D) en utilisant le toucher haptique. Deux séries d'expériences (n = 12 chacune) ont été effectuées. Dans tous les cas, les angles ont été explorés avec l'index du bras tendu. La première expérience a démontré que le seuil de discrimination des angles 2-D a été nettement plus élevé, 7,4°, que le seuil de catégorisation des angles 2-D, 3,9°. Ce résultat étend les travaux précédents, en montrant que la différence est présente dans les mêmes sujets testés dans des conditions identiques (connaissance des résultats, conditions d'essai visuel, l’orientation d’angle). Les résultats ont également montré que l'angle de catégorisation ne varie pas en fonction de l'orientation des angles dans l'espace (oblique, verticale). Étant donné que les angles présentés étaient tous distribués autour de 90°, ce qui peut être un cas particulier comme dans la vision, cette constatation doit être étendue à différentes gammes d'angles. Le seuil plus élevé dans la tâche de discrimination reflète probablement une exigence cognitive accrue de cette tâche en demandant aux sujets de mémoriser temporairement une représentation mentale du premier angle exploré et de la comparer avec le deuxième angle exploré. La deuxième expérience représente la suite logique d’une expérience antérieure dans laquelle on a constaté que le seuil de catégorisation est modifié avec la direction du regard, mais pas avec la position de la tête quand les angles (non visibles) sont explorés en position excentrique, 60° à la droite de la ligne médiane. Cette expérience a testé l'hypothèse que l'augmentation du seuil, quand le regard est dirigé vers l'extrême droite, pourrait refléter une action de l'attention spatiale. Les sujets ont exploré les angles situés à droite de la ligne médiane, variant systématiquement la direction du regard (loin ou vers l’angle) de même que l'emplacement d'angle (30° et 60° vers la droite). Les seuils de catégorisation n’ont démontré aucun changement parmi les conditions testées, bien que le biais (point d'égalité subjective) ait été modifié (décalage aux valeurs inférieurs à 90°). Puisque notre test avec le regard fixé à l’extrême droite (loin) n'a eu aucun effet sur le seuil, nous proposons que le facteur clé contribuant à l'augmentation du seuil vu précédemment (tête tout droit/regard à droite) doit être cette combinaison particulière de la tête/regard/angles et non l’attention spatiale.

Attention! Prêt? On s’enTraine! Étude d’efficacité d’un programme d’entraînement intensif des processus attentionnels chez des jeunes ayant subi un traumatisme craniocérébral

Les dysfonctions attentionnelles suivant un traumatisme craniocérébral (TCC) compliquent souvent la reprise des activités de la vie quotidienne et influencent négativement le pronostic de réinsertion socio-académique et professionnelle. Or, les cliniciens de réadaptation disposent d’un nombre limité d’outils de remédiation cognitive dont l’efficacité est démontrée et qui sont adaptés à une population francophone. Cette étude vise à démontrer l’efficacité d’un protocole d’entrainement intensif des fonctions attentionnelles : « Attention! Prêt? On s’enTraine! » (Séguin, Lahaie & Beauchamp, 2012), basé sur une adaptation française de l’« Attention Process Training-I » (APT-I; Sohlberg & Mateer, 1987). Dix-sept participants ayant subi un TCC et présentant des déficits attentionnels ont reçu 15 séances d’entrainement attentionnel avec le programme « Attention! Prêt? On s’enTraine! » (n = 8) ou de l’aide aux devoirs (n = 9). Suite à l’intervention, les participants du groupe expérimental ont amélioré leur rendement dans plusieurs fonctions ciblées par l’intervention attentionnelle, notamment au niveau du balayage visuel, de l’attention sélective et de l’alternance attentionnelle. De plus, les gains se sont généralisés à des fonctions connexes, puisqu’une meilleure performance a été retrouvée dans des tâches de mémoire de travail, d’inhibition, de flexibilité cognitive et de planification visuoconstructive. La démonstration de l’effet positif d’un entrainement intensif sur le rendement attentionnel pourrait inciter les cliniciens et chercheurs à développer et à valider d’autres protocoles de remédiation cognitive francophones, pour les fonctions attentionnelles ou d’autres sphères de la cognition. Par le fait même, le pronostic fonctionnel de la clientèle pédiatrique en traumatologie en sera potentialisé.

Action preparation helps and hinders perception of action.

Several theories of the mechanisms linking perception and action require that the links are bidirectional, but there is a lack of consensus on the effects that action has on perception. We investigated this by measuring visual event-related brain potentials to observed hand actions while participants prepared responses that were spatially compatible (e.g., both were on the left side of the body) or incompatible and action type compatible (e.g., both were finger taps) or incompatible, with observed actions. An early enhanced processing of spatially compatible stimuli was observed, which is likely due to spatial attention. This was followed by an attenuation of processing for both spatially and action type compatible stimuli, likely to be driven by efference copy signals that attenuate processing of predicted sensory consequences of actions. Attenuation was not response-modality specific; it was found for manual stimuli when participants prepared manual and vocal responses, in line with the hypothesis that action control is hierarchically organized. These results indicate that spatial attention and forward model prediction mechanisms have opposite, but temporally distinct, effects on perception. This hypothesis can explain the inconsistency of recent findings on action-perception links and thereby supports the view that sensorimotor links are bidirectional. Such effects of action on perception are likely to be crucial, not only for the control of our own actions but also in sociocultural interaction, allowing us to predict the reactions of others to our own actions.

The multisensory attentional consequences of tool use: a functional magnetic resonance imaging study

Background: Tool use in humans requires that multisensory information is integrated across different locations, from objects seen to be distant from the hand, but felt indirectly at the hand via the tool. We tested the hypothesis that using a simple tool to perceive vibrotactile stimuli results in the enhanced processing of visual stimuli presented at the distal, functional part of the tool. Such a finding would be consistent with a shift of spatial attention to the location where the tool is used. Methodology/Principal Findings: We tested this hypothesis by scanning healthy human participants' brains using functional magnetic resonance imaging, while they used a simple tool to discriminate between target vibrations, accompanied by congruent or incongruent visual distractors, on the same or opposite side to the tool. The attentional hypothesis was supported: BOLD response in occipital cortex, particularly in the right hemisphere lingual gyrus, varied significantly as a function of tool position, increasing contralaterally, and decreasing ipsilaterally to the tool. Furthermore, these modulations occurred despite the fact that participants were repeatedly instructed to ignore the visual stimuli, to respond only to the vibrotactile stimuli, and to maintain visual fixation centrally. In addition, the magnitude of multisensory (visual-vibrotactile) interactions in participants' behavioural responses significantly predicted the BOLD response in occipital cortical areas that were also modulated as a function of both visual stimulus position and tool position. Conclusions/Significance: These results show that using a simple tool to locate and to perceive vibrotactile stimuli is accompanied by a shift of spatial attention to the location where the functional part of the tool is used, resulting in enhanced processing of visual stimuli at that location, and decreased processing at other locations. This was most clearly observed in the right hemisphere lingual gyrus. Such modulations of visual processing may reflect the functional importance of visuospatial information during human tool use

A psychophysical and computational analysis of the spatio-temporal mechanisms underlying the flash-lag effect

Several accounts put forth to explain the flash-lag effect (FLE) rely mainly on either spatial or temporal mechanisms. Here we investigated the relationship between these mechanisms by psychophysical and theoretical approaches. In a first experiment we assessed the magnitudes of the FLE and temporal-order judgments performed under identical visual stimulation. The results were interpreted by means of simulations of an artificial neural network, that wits also employed to make predictions concerning the F LE. The model predicted that a spatio-temporal mislocalisation would emerge from two, continuous and abrupt-onset, moving stimuli. Additionally, a straightforward prediction of the model revealed that the magnitude of this mislocalisation should be task-dependent, increasing when the use of the abrupt-onset moving stimulus switches from a temporal marker only to both temporal and spatial markers. Our findings confirmed the model`s predictions and point to an indissoluble interplay between spatial facilitation and processing delays in the FLE.

Percepção de tempo e outras funções cognitivas, funcionalidade motora e o nível de atividade física de idosos com Doença de Alzheimer no estágio leve

Pós-graduação em Ciências da Motricidade - IBRC

Negligência unilateral pós-acidente vascular encefálico: atuação da Terapia Ocupacional

Unilateral Neglect Syndrome is one of the consequences of cerebral vascular accident (CVA) generally following right parietal lobe lesion, leading to the impairment of perceptive visual, spatial and attention functions. The patient affected does not realize the environmental stimuli on the contralesional hemibody. Occupational therapy plays an important role in caring for this patient, seeking the recovery of perception, attention and social engagement. This study aimed to describe and evaluate the results of occupational therapy intervention and treatment in a single Unilateral Neglect Syndrome post CVA patient. Data were obtained from a survey of the patient’s medical records and interviews of his therapist and caretaker. The analysis of the patient’s medical records and his therapist’s report showed that the patient responded satisfactorily to treatment, presenting a decrease of the left unilateral neglect at the end of the study period. The favorable outcome of the patient outlined the relevance of evaluating the effects of Occupational Therapy interventions for clinical unilateral neglect syndrome.

Efficacy of a perceptual and visual-motor skill intervention program for students with dyslexia

Purpose: To verify the efficacy of a perceptual and visual-motor skill intervention program for students with dyslexia. Methods: The participants were 20 students from third to fifth grade of a public elementary school in Marília, São Paulo, aged from 8 years to 11 years and 11 months, distributed into the following groups: Group I (GI; 10 students with developmental dyslexia) and Group II (GII; 10 students with good academic performance). A perceptual and visual-motor intervention program was applied, which comprised exercises for visual-motor coordination, visual discrimination, visual memory, visual-spatial relationship, shape constancy, sequential memory, visual figure-ground coordination, and visual closure. In pre- and post-testing situations, both groups were submitted to the Test of Visual-Perceptual Skills (TVPS-3), and the quality of handwriting was analyzed using the Dysgraphia Scale. Results: The analyzed statistical results showed that both groups of students had dysgraphia in pretesting situation. In visual perceptual skills, GI presented a lower performance compared to GII, as well as in the quality of writing. After undergoing the intervention program, GI increased the average of correct answers in TVPS-3 and improved the quality of handwriting. Conclusion: The developed intervention program proved appropriate for being applied to students with dyslexia, and showed positive effects because it provided improved visual perception skills and quality of writing for students with developmental dyslexia.

Influência do gênero na demanda visual por mapas em escalas diferentes em sistema de navegação e guia de rota

This work investigates the gender effect on visual demand of drivers for dynamic maps at different cartographic scales presented In-Vehicle Route Guidance and Navigation System (RGNS). A group of 52 subjects (26 males and 26 females) took part in an experiment performed in a low-cost driving simulator. the driver's task consisted of navigating in an unknown route using a RGNS prototype which presents maps at two different cartographic scales. This paper replicates the known phenomenon of significant relationships between gender and performance at visual-spatial tasks issue. Our results show that drivers of different genders present distinct levels of visual demand both due to the cartographic scales and maneuver complexity variation. These discussed results are based upon individual differences in terms of spatial ability and spatial anxiety.