Velocity prediction in corrective saccades during smooth-pursuit eye movements in monkey

It has been noted in a variety of studies in both humans and monkeys that saccades made during smooth pursuit eye movements are usually quite accurate. Since saccades are known to be planned on the basis of neuronal information existing at some interval of time before the actual onset of the movement, it is generally accepted that some sort of prediction or use of visual motion velocity is combined with static position error in the execution of these saccades to moving targets. However, statistical treatment of this response in humans has provided evidence for alternative mechanisms, including a strategy of saccading ahead in the direction of target motion without any incorporation of actual speed information about target motion in the response. We reinvestigated this question quantitatively in the monkey on a large data base of saccades. We found evidence that supports the hypothesis that information about target speed per se is used in this species in the production of saccades to moving targets. Multiple linear regression analysis supported the hypothesis that information about the position error and the target velocity that exists at about 100 ms prior to the saccade onset are both required to provide a statistical explanation of saccade size during pursuit eye movements under the conditions of our experiments.