The effects of distraction on smooth pursuit in normal subjects.

Smooth pursuit eye movements made in response to 5 and 20% targets were studied in young and old subjects. Tracking of a target was carried out both with no competing stimuli and while auditory and visual distractions were presented. Only tracking the target against a projected background significantly impaired pursuit. It did so in both age groups, by reducing pursuit gain and also by eliciting 'anticipatory saccades', which took the eyes ahead of the target to a new fixation point for 0.5 s or longer. Elderly subjects showed a significantly greater number of such interruptions, however, suggesting that continuous performance of the tracking task could be more readily disrupted in this group. These findings may arise from changes in the way in which elderly individuals process incoming sensory information.