DECREASE IN SACCADIC PERFORMANCE AFTER MANY VISUALLY GUIDED SACCADIC EYE-MOVEMENTS IN MONKEYS

Purpose. To investigate the influence of repeated saccades and of back ground illumination on the metrics and dynamics of visually guided tar geting saccades.Methods. Eye movements were measured by magnetic searc h coil technique in seven trained monkeys (Macaca mulatta) while they performed many visually guided saccades in the dark or in dim backgrou nd light. Results. After 2000 to 7000 saccades in the dark, peak eye v elocity on the average decreased by 20%, saccadic gain decreased sligh tly by 4.5%, and saccadic latency increased by 15%. All parameters als o showed increased variability. In contrast, when testing was done in dim light, there was little to no change in average saccadic metrics a nd latency. Conclusions. The changes in saccadic metrics and dynamics in the dark do not reflect a change of the ocular plant but may reflec t a change in the cortical or cerebellar influences on the brain stem burst generator linked to the monkeys' attentional state. Background l ight mostly prevents this change.