Prediction of saccadic amplitude during smooth pursuit eye movements

If humans try to pursue a moving target, the nervous system uses predictions to overcome some of the nervous systems delays. It is therefore possible for the eyes to pursue a target with virtually no delay and to make accurate catch-up saccades to moving targets. Another example of a delay is the latency of a saccade made in response to a target step. Due to imperfect pursuit, the retinal error will change during this latency. The aim of the present study was to investigate whether step-induced saccades take into account this change. To vary this change in retinal error, the gain of the pursuit eye movement was manipulated successfully by adding a patterned background in one condition and a concomitant hand tracking in another. The increased gain of the pursuit eye movements in the hand tracking condition significantly modified the change in retinal error during the latency. However, no significant differences in saccadic amplitude were found between conditions. We conclude that these step-induced saccades are generated independently of the gain of the pursuit eye movement. (C) 2000 Elsevier Science B.V. All rights reserved. PsycINFO classification. 2300; 2323; 2330.