Eye-hand coordination during visuomotor adaptation: effects of hemispace and joint coordination.

We previously examined adaptive changes of eye-hand coordination during learning of a visuomotor rotation. Gazes during reaching movements were initially directed to a feedback cursor in early practice, but were gradually shifted toward the target with more practice, indicating an emerging gaze anchoring behavior. This adaptive pattern reflected a functional change of gaze control from exploring the cursor-hand relation to guiding the hand to the task goal. The present study further examined the effects of hemispace and joint coordination associated with target directions on this behavior. Young adults performed center-out reaching movements to four targets with their right hand on a horizontal digitizer, while looking at a rotated visual feedback cursor on a computer monitor. To examine the effect of hemispace related to visual stimuli, two out of the four targets were located in the ipsilateral workspace relative to the hand used, the other two in the contralateral workspace. To examine the effect of hemispace related to manual actions, two among the four targets were related to reaches made in the ipsilateral workspace, the other two to reaches made in the contralateral workspace. Furthermore, to examine the effect of the complexity of joint coordination, two among the four targets were reaches involving a direct path from the start to the target involving elbow movements (simple), whereas the other two targets were reaches involving both shoulder and elbow movements (complex). The results showed that the gaze anchoring behavior gradually emerged during practice for reaches made in all target directions. The speed of this change was affected mainly by the hemispace related to manual actions, whereas the other two effects were minimal. The gaze anchoring occurred faster for the ipsilateral reaches than for the contralateral reaches; gazes prior to the gaze anchoring were also directed less at the cursor vicinity but more at the mid-area between the starting point and the target. These results suggest that ipsilateral reaches result in a better predictability of the cursor-hand relation under the visuomotor rotation, thereby prompting an earlier functional change of gaze control through practice from a reactive to a predictive control.