Title: Oral presentation
Author: eggert
Last saved by: Robin Hill
Company: NEFO

The influence of retinal position error and target velocity on saccades in monkey.

T. Eggert, Y.-F. Guan, O. Bayer, U. Büttner
Department of Neurology, Ludwig-Maximilians University, Munich, Germany
eggert@nefo.med.uni-muenchen.de 

The retinal position error is the main factor determining amplitude, peak velocity and duration of saccades, made to stationary visual targets. We investigated whether the stereotypical relation between these saccade parameters is identical for moving and stationary targets and how this relation might be affected by target velocity.
After jumping to an initial position, the target either remained stationary at this position or moved forward or backward with constant velocity (10 deg/s). The pursuit component was eliminated from the data by subtracting the smooth pursuit component from eye velocity. 
When comparing saccades with the same amplitude (6.5 deg) to forward and backward moving targets, we found that the peak velocities differed. More specifically, saccades to backward-moving targets showed higher peak velocity (244 deg/s) and shorter duration (50.2 ms) than saccades to forward-moving targets (peak velocity: 204 deg/s; duration: 58.1 ms). The duration of saccades to moving targets decreased with increasing peak velocity whereas saccades to stationary targets typically show increasing duration with increasing peak velocity. This suggests that one single parameter, e.g. the retinal error, cannot explain all parameters of the saccade. The target velocity most probably also affects the saccade. Further analysis revealed that the peak velocity can be explained only by the retinal position error,  whereas the saccade amplitude depends on both position error and target velocity. This suggests that target velocity affects the saccade mainly after the peak velocity, i.e. during the deceleration phase of the saccade.