Moving your head reduces perisaccadic compression

Abstract

Stimuli that are presented briefly near the time of a saccadic gaze shift tend to be judged to have been closer to where the gaze ended than they really were. The resulting perisaccadic compression of perceived positions is probably related to uncertainty about the direction of gaze at the time of the flash. The larger the shift in gaze the stronger the compression, possibly because the uncertainty increases with the magnitude of the motor commands that give rise to the change in gaze. If so, then performing part of the gaze shift by moving one's head may decrease the compression, because the combined uncertainty of eye and head orientation in a combined eye-head gaze shift will be smaller than the uncertainty of the eye when it shifts gaze on its own. To test whether reducing eye-in-head movement by moving the head reduces perisaccadic compression for a given shift in gaze, we asked participants to shift their gaze between two positions, either without moving their head or with the head contributing to the change in gaze. We flashed targets around the time of the saccades and participants indicated where they saw these targets. Although allowing head movements did not affect the amplitude and velocity of the gaze shifts, the eye-in-head movements and their peak velocities were obviously larger when only the eyes moved, than when both the eyes and the head contributed to the change in gaze. There was also significantly more compression when only the eyes moved than when both the eyes and head moved. We conclude that moving one's head can reduce the magnitude of the systematic mislocalization that is observed near the time of rapid shifts of gaze. Meeting abstract presented at VSS 2014