Delay of gaze fixation during reaching movement with the non-dominant hand to a distant target.

The present study examined the effects of hand and task difficulty on eye-hand coordination related to gaze fixation behavior (i.e., fixating a gaze to the target until reach completion) in single reaching movements. Twenty right-handed young adults made reaches on a digitizer, while looking at a visual target and feedback of hand movements on a computer monitor. Task difficulty was altered by having three target distances. In a small portion of trials, visual feedback was randomly removed at the target presentation. The effect of a moderate amount of practice was also examined using a randomized trial schedule across target-distance and visual-feedback conditions in each hand. The results showed that the gaze distances covered during the early reaching phase were reduced, and the gaze fixation to the target was delayed when reaches were performed with the left hand and when the target distance increased. These results suggest that when the use of the non-dominant hand or an increased task difficulty reduces the predictability of hand movements and its sensory consequences, eye-hand coordination is modified to enhance visual monitoring of the reach progress prior to gaze fixation. The randomized practice facilitated this process. Nevertheless, variability of reach trajectory was more increased without visual feedback for right-hand reaches, indicating that control of the dominant arm integrates more visual feedback information during reaches. These results together suggest that the earlier gaze fixation and greater integration of visual feedback during right-hand reaches contribute to the faster and more accurate performance in the final reaching phase.