The locus of age-related movement slowing: sensory processing in continuous goal-directed aiming.

Prolonged movement times in elderly persons have been well documented; however, the locus of this slowing is uncertain. Kinematic analysis of discrete aiming has revealed deficits primarily in the target approach phase, suggesting inefficient feedback processing. This study investigated age-related movement slowing in a continuous aiming task, for which movements are mediated by feedforward and on-line sensory processes. Two-dimensional video-recordings were made of young and elderly adults performing reciprocal tapping using the right and left hands under three different accuracy conditions. The elderly subjects exhibited more discrete adjustments in the trajectories coupled with longer times in this period. Further, the elderly spent more time reversing direction between target hits, especially in the high accuracy condition. Longer time on target was seen in the left-hand performance of the elderly. Results suggest that the locus of age-related slowing in the performance of continuous aiming may reflect a greater dependence on slower feedback processes instead of rapid, on-line, and feedforward sensory processes. Age-related differences in hand performance may provide further insight into central processing deficits.