PLANIFICATION ET CONTROLE EN TEMPS REEL D'UN MOUVEMENT DE POINTAGE OU DE SAISIE D'UNE CIBLE VISUELLE (UNE APPROCHE PLURIDISCIPLINAIRE)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Integration of visual information for saccade production

International audienceTo foveate a visual target, subjects usually execute a primary hyp-ometric saccade (S1) bringing the target in perifoveal vision, followed by a corrective saccade (S2) or by more than one S2. It is still debated to what extent these S2 are pre-programmed or dependent only on post-saccadic retinal error. To answer this question , we used a visually-triggered saccade task in which target position and target visibility were manipulated. In one-third of the trials, the target was slightly displaced at S1 onset (so-called double step paradigm) and was maintained until the end of S1, until the start of the first S2 or until the end of the trial. Experiments took place in two visual environments: in the dark and in a dimly lit room with a visible random square background. The results showed that S2 were less accurate for shortest target durations. The duration of post-saccadic visual integration thus appears as the main factor responsible for corrective saccade accuracy. We also found that the visual context modulates primary saccade accuracy , especially for the most hypometric subjects. These findings suggest that the saccadic system is sensitive to the visual properties of the environment and uses different strategies to maintain final gaze accuracy

Effects of short-term adaptation of saccadic gaze amplitude on hand-pointing movements

International audienceWe investigated whether and how adaptive changes in saccadic amplitudes (short-term saccadic adaptation) modify hand movements when subjects are involved in a pointing task to visual targets without vision of the hand. An experiment consisted of the pre-adaptation test of hand pointing (placing the finger tip on a LED position), a period of adaptation, and a post-adaptation test of hand pointing. In a basic task (transfer paradigm A), the pre-and post-adaptation trials were performed without accompanying eye and head movements: in the double-step gaze adaptation task, subjects had to fixate a single, suddenly displaced visual target by moving eyes and head in a natural way. Two experimental sessions were run with the visual target jumping during the saccades, either backwards (from 30 to 20°, gaze sac-cade shortening) or onwards (30 to 40°, gaze saccade lengthening). Following gaze-shortening adaptation (level of adaptation 79±10%, mean and s.d.), we found a statistically significant shift (t-test, error level P<0.05) in the final hand-movement points, possibly due to adaptation transfer, representing 15.2% of the respective gaze adaptation. After gaze-lengthening adaptation (level of adaptation 92±17%), a non-significant shift occurred in the opposite direction to that expected from adaptation transfer. The applied computations were also performed on some data of an earlier transfer paradigm (B, three target displacements at a time) with gain shortening. They revealed a significant transfer relative to the amount of adaptation of 18.5±17.5% (P<0.05). In the coupling paradigm (C), we studied the influence of gaze saccade adaptation of hand-pointing movements with concomitant orienting gaze shifts. The adaptation levels achieved were 59±20% (shortening) and 61±27% (lengthening). Shifts in the final fingertip positions were congruent with internal coupling between gaze and hand, representing 53% of the respective gaze-amplitude changes in the shortening session and 6% in the lengthening session. With an adaptation transfer of less than 20% (paradigm A and B), we concluded that saccadic adaptation does not " automatically " produce a functionally meaningful change in the skeleto-motor system controlling hand-pointing movements. In tasks with concomitant gaze saccades (coupling paradigm C), the modification of hand pointing by the adapted gaze comes out more clearly, but only in the shortening session

Enhancing Visuomotor Adaptation by Reducing Error Signals: Single-step (Aware) versus Multiple-step (Unaware) Exposure to Wedge Prisms

International audienceNeglect patients exhibit both a lack of awareness for the spatial distortions imposed during visuomanual prism adaptation procedures, and exaggerated postadaptation negative after-effects. To better understand this unexpected adaptive capacity in brain-lesioned patients, we investigated the contribution of awareness for the optical shift to the development of prism adaptation. The lack of awareness found in neglect was simulated in a multiple-step group where healthy subjects remained unaware of the optical deviation because of its progressive stepwise increase from 2 degrees to 10 degrees . We contrasted this method with the classical single-step group in which subjects were aware of the visual shift because they were directly exposed to the full 10 degrees shift. Because the number of pointing trials was identical in the two groups, the total amount of deviation exposure was 50% larger in the single-step group. Negative after-effects were examined with an open-loop pointing task performed with the adapted hand, and generalization was tested with open-loop pointing with the nonexposed hand to visual and auditory targets. The robustness of adaptation was assessed by an open-loop pointing task after a simple de-adaptation procedure. The progressive, unaware condition was associated with larger negative after-effects, transfer to the non-exposed hand for the visual and auditory pointing tasks, and greater robustness. The amount of adaptation obtained remained, nevertheless, lower than the exaggerated adaptive capacity seen in patients with neglect. Implications for the functional mechanisms and the anatomical substrates of prism adaptation are discussed

Posture-movement co-ordination when reaching in immersive visual virtual environment

International audienceThe virtual reality is more and more applied in neurobehavioural experiment such as goal-directed hand movement and postural equilibrium. However, VE exposure often causes errors in the visual guidance of motor activities. Consequently, the development of the virtual environment must take into account the visuomotor transformation principles. The goal of this study was to identify how movement and balance motor commands are co-ordinated in order to integrate the unexpected modification of visual virtual scene

Evaluating on-line control of goal-directed arm movement while standing in virtual visual environment

International audienceThe control of visually guided movement has been showed to be optimised when motor programming quickly integrated the visual information to update on-going motor commands. The purpose of this study was to verify this proposition for movement executed in virtual visual environment (VE), by exploring the effect of immersion on the on-line visuomotor control of goal-directed arm movement. Six subjects participated in the experiment, in which hand reaching toward a stationary or a moving virtual visual target (double step paradigm) was executed in standing posture. The analysis of the hand kinematics and postural adjustment showed an accurate control of movement and balance in both reaching conditions. This indicates that the immersion do not affects the on-line control processes used by the CNS to adjust movement in interactive VE