Saccadic updating of object orientation for grasping movements.

Reach and grasp movements are a fundamental part of our daily interactions with the environment. This spatially-guided behavior is often directed to memorized objects because of intervening eye movements that caused them to disappear from sight. How does the brain store and maintain the spatial representations of objects for future reach and grasp movements? We had subjects (n=8) make reach and two-digit grasp movements to memorized objects, briefly presented before an intervening saccade. Grasp errors, characterizing the spatial representation of object orientation, depended on current gaze position, with and without intervening saccade. This suggests that the orientation information of the object is coded and updated relative to gaze during intervening saccades, and that the grasp errors arose after the updating stage, during the later transformations involved in grasping. The pattern of reach errors also revealed a gaze-centered updating of object location, consistent with previous literature on updating of single-point targets. Furthermore, grasp and reach errors correlated strongly, but their relationship had a non-unity slope, which may suggest that the gaze-centered spatial updates were made in separate channels. Finally, the errors of the two digits were strongly correlated, supporting the notion that these were not controlled independently to form the grip in these experimental conditions. Taken together, our results suggest that the visuomotor system dynamically represents the short-term memory of location and orientation information for reach-and-grasp movements.