Decrease in saccadic performance after many visually guided saccadic eye movements in monkeys.

PURPOSE

To investigate the influence of repeated saccades and of background illumination on the metrics and dynamics of visually guided targeting saccades.

METHODS

Eye movements were measured by magnetic search coil technique in seven trained monkeys (Macaca mulatta) while they performed many visually guided saccades in the dark or in dim background light.

RESULTS

After 2000 to 7000 saccades in the dark, peak eye velocity on the average decreased by 20%, saccadic gain decreased slightly by 4.5%, and saccadic latency increased by 15%. All parameters also showed increased variability. In contrast, when testing was done in dim light, there was little to no change in average saccadic metrics and latency.

CONCLUSIONS

The changes in saccadic metrics and dynamics in the dark do not reflect a change of the ocular plant but may reflect a change in the cortical or cerebellar influences on the brain stem burst generator linked to the monkeys attentional state. Background light mostly prevents this change.