The Role of the Caudal Superior Parietal Lobule in Updating Hand Location in Peripheral Vision: Further Evidence from Optic Ataxia

Patients with optic ataxia (OA), who are missing the caudal portion of their superior parietal lobule (SPL), have difficulty performing visually-guided reaches towards extra-foveal targets. Such gaze and hand decoupling also occurs in commonly performed non-standard visuomotor transformations such as the use of a computer mouse. In this study, we test two unilateral OA patients in conditions of 1) a change in the physical location of the visual stimulus relative to the plane of the limb movement, 2) a cue that signals a required limb movement 180° opposite to the cued visual target location, or 3) both of these situations combined. In these non-standard visuomotor transformations, the OA deficit is not observed as the well-documented field-dependent misreach. Instead, OA patients make additional eye movements to update hand and goal location during motor execution in order to complete these slow movements. Overall, the OA patients struggled when having to guide centrifugal movements in peripheral vision, even when they were instructed from visual stimuli that could be foveated. We propose that an intact caudal SPL is crucial for any visuomotor control that involves updating ongoing hand location in space without foveating it, i.e. from peripheral vision, proprioceptive or predictive information

Rise and fall of the two visual systems theory

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Visual perception is dependent on visuospatial working memory and thus on the posterior parietal cortex

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Optic ataxia: beyond the dorsal stream cliché

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L'ego Légo® : déconstruire et reconstruire le cerveau-esprit ?

The deconstruction or the reconstruction of the mind-brain ? Cognitive neurosciences have contributed a substantial set of data which demonstrate the existence of two or several distinct systems, implicit and explicit, which participate in a single function : the identification of an object or a face, the spatial localisation of a target, the production of an action, the memory of an event, or even the attribution of a thought to another person or the emotional reaction to an event. In particular, the study of perception shows a hiatus between a conscious representation and what is represented, in the sense that this representation is an interpretation of the world. But it is to be noted that this hiatus is not compatible with survival of the individual, which implies responses precisely adapted to the properties -both semantic and physical -of the environment. When it is a case of producing an immediate action, the hand must reach its goal and the fingers must conform to the real object which is to be grasped. The internal visual (re)presentations which enter into play in the course of a simple action must therefore conform strictly to physical space, which implies the existence of an "immaculate perception", quite distinct from the conscious representation. Particular characteristics, of a neuro-anatomical and physiological order, of a spatial or even temporal order, can thus be attributed respectively to each of these two modes of processing sensory information. By refining these distinctions, one can thus divide each functional system into a number of identifiable sub-systems. The question which is thus posed is to know how these various representations can interact or be integrated. Recent results show that interactions between two perceptive sub-systems (the cognitive and the sensory-motor sub-systems) are possible, even if they are strictly dependent on temporal constraints. At the present time it seems that the task of the integrative neurosciences converges with the task achieved each moment by the brain : in the same way that in order for consciousness to appear, biological matter must necessarily effect a synthesis (of a spatial or temporal order) of the operations which are carried out in a distributed fashion in time and space, scientists must somehow manage to achieve a synthesis of the fragmented (and divided) items of knowledge acquired by the brain, in order to succeed in presenting coherent hypotheses concerning the genesis of the phenomena of consciousness. The aim is thus to conceptualize brain functioning in the complexity of the interactions which exist between the different zones and sub-systems which have been identified, and to specify the limits and the constraints on these interactions, notably in the temporal domain. The current challenge to the neurosciences is not to divide ever further the matter of the brain in order to rule over the mind, but to try to reconstruct the entity which is the brain as a whole, or it may even be hoped, the mind-brain.Les neurosciences cognitives ont apporté un important ensemble de données démontrant l'existence de deux ou plusieurs systèmes distincts, implicites et explicites, participant d'une même fonction : identifier un objet ou un visage, localiser une cible dans l'espace, produire une action, mémoriser un événement, ou même attribuer une pensée à autrui ou réagir affectivement à un événement. En particulier, l'étude de la perception met en évidence un hiatus entre la représentation consciente et ce qu'elle représente, dans le sens où cette représentation est une interprétation du monde. Mais on peut remarquer que ce hiatus n'est pas compatible avec la survie individuelle, qui implique des réponses précisément adaptées aux propriétés non seulement sémantiques mais aussi physiques de l'environnement. Lorsqu'il s'agit de produire une action immédiate : la main doit atteindre son but, et les doigts se conformer à l'objet, bien réel, à saisir. Les (re)présentations visuelles internes mises en jeu lors d'une action simple se doivent donc d'être strictement conformes à l'espace physique, ce qui permet d'évoquer l'existence d'une " immaculée perception ", bien distincte de la représentation consciente. Des caractéristiques particulières, d'ordre neuro-anatomique et physiologique, d'ordre spatial ou même temporel, peuvent ainsi être attribuées respectivement à chacun de ces deux modes de traitement de l'information sensorielle. En affinant ces distinctions, on peut ainsi diviser chaque système fonctionnel en de nombreux sous-systèmes identifiés. La question se pose alors de savoir comment ces représentations peuvent interagir ou être intégrées. Des résultats récents montrent que des interactions entre deux sous-systèmes perceptifs (cognitif et sensori-moteur) sont possibles, même si elles sont étroitement dépendantes de contraintes temporelles. Il semble à l'heure actuelle que la tâche des neurosciences intégrées rejoigne celle réalisée à chaque instant par le cerveau : de la même façon que la matière biologique doit nécessairement opérer une synthèse (d'ordre spatial ou temporel) des opérations réalisées de façon distribuées dans le temps et l'espace cérébral pour faire apparaître la conscience, les chercheurs doivent s'efforcer de faire la synthèse des connaissances morcelées (et divisantes) acquises sur le cerveau pour arriver à présenter des hypothèses cohérentes sur la genèse des phénomènes de conscience. Il s'agit donc de concevoir le fonctionnement cérébral dans la complexité des interactions qui existent entre différentes aires et les différents sous-systèmes identifiés, et de préciser les limites et les contraintes de ces interactions, notamment dans le domaine temporel. Le défi actuel des neuroscientifiques n'est donc plus de diviser encore plus avant la matière cérébrale pour régner sur l'esprit, mais de tenter une reconstitution de cette entité que constitue le cerveau, ou même faut-il l'espérer, l'esprit-cerveau.Rossetti Yves, Pisella Laure. L'ego Légo® : déconstruire et reconstruire le cerveau-esprit ?. In: Intellectica. Revue de l'Association pour la Recherche Cognitive, n°31, 2000/2. Recherches sur la conscience en sciences cognitives. pp. 137-173

New insights on eye blindness and hand sight: Temporal constraints of visuo-motor networks

International audiencePioneer experiments on saccadic suppression have shown that this effect is not followed by motor disorientation: Conscious perception of a target displacement can be dissociated from correct manual target reaching. It has subsequently been demonstrated that movement corrections with the same latency and spatial characteristics can be produced in conditions allowing perceptual awareness of perturbation of a target as in condition inducing saccadic suppression. In addition to the qualitative dissociation between motor performance and conscious awareness , quantitative temporal dissociations in action can be observed by manipulating different features of the visual target. When the target of an ongoing simple action is perturbed, a temporal advantage is found for responses to perturbations of location relative to colour and shape. Furthermore, there seems to be a temporal advantage for automatic motor corrections made in response to a target displacement as compared to other responses (other ongoing movement adjustments , movement interruption, conditional motor response such as pressing a key, verbal response, delayed matching-to-sample tasks). Thus, this paper reviews evidence for the fact that the temporal characteristics of any given response to a stimulus are dependent both on the sensory processes and on the type of response generated. Accordingly, identification responses (such as verbal report) to a visual stimulus are much slower than motor corrections of an ongoing movement in response to a target location change because of different processing times of the stimulus features ("What" compared to "Where") and of the response itself ("What" compared to "How"). The existence of two continua (What/Where and What/How) is proposed between these two extreme stimulus-response combinations. This model may be a useful framework to better understand visuo-motor transformations and the network of connections between visual and motor areas

Causal evidence for posterior parietal cortex involvement in visual-to-motor transformations of reach targets

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Optic ataxia revisited:

International audienceOptic ataxia and visual agnosia have been proposed to constitute a double dissociation which provides the main argument for the assimilation of the anatomical distinction between a dorsal and a ventral visual stream to the functional distinction between perception and action. In the present review, we argue that insufficient evidence has been collected to argue for this double dissociation. Several criteria are reviewed: (1) exploration of the visuomotor behavior in central versus peripheral vision has not been matched for the two types of patients; (2) the temporal constraints of visual processes that are impaired in the two neurological conditions appear to play a crucial role in the apparent dissociation; (3) the necessary reductionism of experimental conditions used to study action has led to an overconsideration of optic ataxia as a global deficit for action. Altogether optic ataxia appears to result from a specific impairment of immediate visuomotor control rather than of visually guided action as a whole. These results are discussed in the light of recent research on optic ataxia and on motor control, and directions for future research are proposed

Using eye movements to explore mental representations of space

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The posterior parietal cortex processes visuo-spatial and extra-retinal information for saccadic remapping: A case study

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