Smooth pursuit initiation in young and elderly subjects.

Smooth pursuit initiation to step-ramp stimuli was investigated in normal subjects, young and elderly. Older subjects had significant reductions in initial pursuit acceleration before saccades, and in post-saccadic and peak pursuit velocities. Aging impairs the open-loop performance of the pursuit system, possibly by decreasing sensitivity to retinal image motion or by limiting the conversion of visual motion signals into commands for smooth pursuit. Lower open-loop pursuit gain degrades steady-state, closed-loop smooth pursuit in senescence. Our elderly subjects also made less accurate saccades to moving targets, implying defective use of visual motion information by the saccadic system.