Reaching within a dynamic virtual environment

Background: Planning and execution of reaching requires a series of computational processes that involve localization of both the target and initial arm position, and the translation of this spatial information into appropriate motor commands that bring the hand to the target. We have investigated the effects of shifting the visual field on visuomotor control using a virtual visual environment in order to determine how changes in visuo-spatial relations alter motor planning during a reach. Methods: Five healthy subjects were seated in front of an immersive, stereo virtual scene while reaching for a visual target that remained stationary in space or unpredictably shifted to a second position ( either to the right or left of the first target) with different inter-stimulus intervals. Motion of the scene either matched the motion of their head or was rotated counter clockwise at 130 deg/ s in the roll plane. Results: Initial results suggested that both the temporal and spatial aspects of reaching were affected by a rolling visual field. Subjects were able to amend ongoing motion to match target position regardless of scene motion, but the presence of visual field motion produced significantly longer pauses during the reach movement when the target was shifted in space. In addition, terminal arm posture exhibited a drift in the direction opposite to the roll motion. Conclusion: These findings suggest that roll motion of the visual field of view interfered with the ability to imultaneously process two consecutive stimuli. Observed changes in arm position following the termination of the reach suggest that subjects were compensating for a perceived change in their visual reference frame.