Patrick Pe ruch

The effects of available visual information in the periphery (enlargement of the functional visual field) on performance in navigation were evaluated in an experimental setup searching for a "compromise" between desktop and head-immersion situations. A Fixed Vision condition (fixed display) and two Mobile Vision conditions (head-tracking with a visual field of variable width) were compared in six virtual environments of different complexity and in four successive sessions. First, a global improvement in performance throughout the sessions revealed a gradual integration of the properties of the simulation device. Second, performance was higher in the Mobile Vision conditions, as shown by the smoothness of the subjects' paths (sharp curves could be negotiated without stopping), indicating the importance of a wide functional visual field. In conclusion, the need to design realistic and functionaly efficient human-machine interfaces for navigation is discussed.

Unilateral vestibular loss impairs external space representation.

The vestibular system is responsible for a wide range of postural and oculomotor functions and maintains an internal, updated representation of the position and movement of the head in space. In this study, we assessed whether unilateral vestibular loss affects external space representation. Patients with Menière's disease and healthy participants were instructed to point to memorized targets in near (peripersonal) and far (extrapersonal) spaces in the absence or presence of a visual background. These individuals were also required to estimate their body pointing direction. Menière's disease patients were tested before unilateral vestibular neurotomy and during the recovery period (one week and one month after the operation), and healthy participants were tested at similar times. Unilateral vestibular loss impaired the representation of both the external space and the body pointing direction: in the dark, the configuration of perceived targets was shifted toward the lesioned side and compressed toward the contralesioned hemifield, with higher pointing error in the near space. Performance varied according to the time elapsed after neurotomy: deficits were stronger during the early stages, while gradual compensation occurred subsequently. These findings provide the first demonstration of the critical role of vestibular signals in the representation of external space and of body pointing direction in the early stages after unilateral vestibular loss

Vestibular information is necessary for maintaining metric properties of representational space: evidence from mental imagery

International audienceThe vestibular system contributes to a wide range of functions, from postural and oculomotor reflexes to spatial representation and cognition. Vestibular signals are important to maintain an internal, updated representation of the body position and movement in space. However, it is not clear to what extent they are also necessary to mentally simulate movement in situations that do not involve displacements of the body, as in mental imagery. The present study assessed how vestibular loss can affect object-based mental transformations (OMTs), i.e., imagined rotations or translations of objects relative to the environment. Participants performed one task of mental rotation of 3D-objects and two mental scanning tasks dealing with the ability to build and manipulate mental images that have metric properties. Meniere's disease patients were tested before unilateral vestibular neurotomy and during the recovery period (1 week and 1 month). They were compared to healthy participants tested at similar time intervals and to bilateral vestibular-defective patients tested after the recovery period. Vestibular loss impaired all mental imagery tasks. Performance varied according to the extent of vestibular loss (bilateral patients were frequently the most impaired) and according to the time elapsed after unilateral vestibular neurotomy (deficits were stronger at the early stage after neurotomy and then gradually compensated). These findings indicate that vestibular signals are necessary to perform OMTs and provide the first demonstration of the critical role of vestibular signals in processing metric properties of mental representations. They suggest that vestibular loss disorganizes brain structures commonly involved in mental imagery, and more generally in mental representation. (C) 2011 Elsevier Ltd. All rights reserved

Route and survey processing of topographical memory during navigation

International audienceWe investigated the characteristics of route and survey processing of a unique complex virtual environment both at the behavioral and brain levels. Prior to fMRI scanning, participants were trained to follow a route and to learn the spatial relationships between several places, acquiring both route and survey knowledge from a ground-level perspective. During scanning, snapshots of the environment were presented, and participants were required to either indicate the direction to take to follow the route (route task), or to locate unseen targets (survey task). Data suggest that route and survey processing are mainly supported by a common occipito-fronto-parieto-temporal neural network. Our results are consistent with those gathered in studies concerning the neural bases of route versus survey knowledge acquired either from different perspectives or in different environments. However, rather than arguing for a clear distinction between route and survey processing, “mixed” strategies are likely to be involved when both types of encoding take place in the same environment

Demographic and clinical data for the patients and controls.

<p>"-" indicates data not available.</p

Schematic representation of the experimental setup for the pointing tasks: sagittal view (top) and top-view (bottom).

<p>The participant was seated in front of the three spaces on which red dots were projected as target stimuli. When the target disappeared, the participant moved the laser pointer to the memorized location. From the observer's position, the horizontal near and far spaces correspond to a viewing angle of approximately 40×24 degrees and 35×12 degrees in the horizontal plane, respectively. The vertical space corresponds to a viewing angle of approximately 26×19 degrees in the vertical plane. At bottom, the top-view shows the two concentric rectangles and the angular distribution of the targets in the near and far spaces. In the experiment, the rectangles are formed with white stripes on a black backdrop and are visible only in the light condition.</p