Aging and saccade-stepping interactions in humans.

Saccade-stepping interactions were compared in older and young persons to determine if visual anchoring theory could be applied to stepping behavior in both groups. Subjects rapidly stepped onto a platform. In some trials, a translucent shield was used to prevent visual fixation. Both elderly and younger subjects initiated downward saccades prior to footlift, but saccade-step latency was significantly longer for the elderly. Regardless of age, working memory was not sufficient to guide stepping in the absence of visual fixation. The findings support visual anchoring theory by demonstrating that older and young persons generate anticipatory downward saccades which precede the stepping action. Changes in the latency of saccade-step coupling with aging were attributed to slowed processing of visual anchors for obstacle avoidance. The central nervous system appears to accommodate age-related processing delays by initiating the down saccade well in advance of platform footlift, independently from stepping velocity.