Effects of hand termination and accuracy requirements on eye-hand coordination in older adults.

This study investigated how aging compromises the control of saccades and eye-hand coordination when accuracy constraints and termination requirements of hand movement are altered. Seventeen older adults and seventeen young controls performed two-segment aiming movements. The first segment had two target sizes to alter accuracy constraints. Two-segment eye movements were always made to first and second targets, whereas hand movements were varied across three hand-movement types with different termination requirements: (1) stop both at the first and second targets, (2) stop at the first target and discontinue, and (3) move through the first target and discontinue. Compared to the young adults, the older adults produced hypometric primary saccades and delayed gaze fixation to the first target. The older adults also modified eye movements less depending on the hand termination and accuracy requirements. After pointing completion to the first target, the older adults maintained their gaze fixation to that target for a longer duration than young adults. However, this prolonged gaze fixation was minimized when a hand termination was not required. Conversely, the prolongation of gaze fixation was magnified when the hand termination was required at the first target while the eye movement was continuing to the next target. Thus, older adults have difficulties in concurrent control of inhibiting hand movement and initiating eye movement at a target within a sequence. Taken together, it is suggested that aging reduces the ability to modify eye movements to meet various behavioral constraints imposed on manual aiming tasks.