Motion perception during saccades.

Although the retinal image is displaced by each saccade performed we do not perceive the visual environment moving concordant with the saccades. In this study experiments were designed in which additional movement of most of the visual scene was applied during saccades. The subjects perceived the intrasaccadic movement after the saccade. The perceived speed of this movement was decreased and the threshold amplitude was increased compared to perception during fixation. The intrasaccadic movement perception was based on a novel aftereffect of motion perception. The velocity of retinal slip did not affect the threshold. If the retinal slip speed during saccades was temporally reduced by an intrasaccadic movement parallel to the saccade, the threshold amplitude was identical to the threshold amplitude obtained by intrasaccadic movement opposite to the saccade increasing retinal slip speed. Horizontal intrasaccadic movements were detected at lower thresholds than vertical movements independent of saccade direction. In addition, the thresholds were not effected by the saccade amplitude suggesting that neither speed, duration, nor direction of eye movement related retinal slip affects the amount of suppression. Our results suggest that saccadic suppression is related to delayed central processing of retinal information during saccades. This processing does not involve saccade parameters such as direction and amplitude.