Caractéristiques des corrections automatiques assurant la précision spatiale d’un mouvement d’atteinte manuelle

Manual aiming movements are probably the most common motor activities in humans. Researchers have long thought that the initial driving impulse of this type of movement was ballistic, that it could not be modified along the way. However, recent studies suggest that this is not the case and that this first movement impulse could be smoothly modulated on the basis of visual afferent information.  To study this phenomenon, several authors used a video pointing task in which a cursor, representing the hand of a participant, was moved to a visual target. To investigate possible movement execution correction mechanisms, the target or the cursor representing the participant's hand was sometimes moved laterally (for example 15 mm to the right) soon after movement initiation. In order to reach the target, the participant had to correct the movement he had initiated based on the new visual information available. In the present dissertation, we wanted to determine the characteristics of these online corrections. Our results indicate: - That two successive perturbations do not conflict with one another. Specifically, the presentation of a second perturbation does not interfere with the correction process set in motion by the first perturbation. These results confirm that visual afferent information is processed online during movement execution. In addition, these results underline the low attentional load associated with the processing of the visual information concerning the displacement of the cursor and the planning and initiation of an appropriate correction. - That to see the cursor displaced from its original trajectory for as little as 16 ms is enough to observe a correction of the initial movement trajectory. In addition, the magnitude of the correction observed increases when the period of cursor visibility increases following the perturbation. We used these results to demonstrate that the central nervous system evaluated the perceived position of the hand following the spatial integration of its position over the last 70 milliseconds. - That the latency of the correction is not dependent on the magnitude of the perturbation or where it occurs in the movement trajectory. However, the gain of this correction depends on the magnitude of the perturbation. These observations suggest that the planning of the correction is based on a comparison between the planned and the observed movement trajectories. The gain of the correction would rather depend on the perceived position of the hand and the characteristics of the target to reach (location and dimension). In conclusion, the results of this dissertation show an impressive efficiency of the visual system for the detection and correction of movement planning or execution errors. A fast and accurate system that requires minimal attentional demands. It does appear that manual aiming movements are under the continuous control of visual afferent information.

Keyphrases: vision, perturbation, Motor control, vision, online correction, online movement modulation, video aiming, perturbation, cursor jump, continuous processing