University Archives

Asymmetries in pre saccadic fixation durations have been observed between vertical saccades, such that pre-saccadic f ixation durations for down-directed saccades are significantly longer compared to up-directed saccades. The present study was designed to test our theory that the release of saccades into the upper visual field (UpVF) is more weakly inhibited than the release of saccades into the lower visual f ield (LoVF). We predict flickering distractors in the UpVF will be most disruptive to up-directed saccades. 13 healthy adults wore an eye-tracker and completed 3 blocks containing 42 trials of a gaze contingent low contrast visual search task. For the distractor conditions, participants were instructed to ignore a 4 Hz steady-state flickering light strip positioned above or below the search plane. We replicated the vertical asymmetries observed in pre-saccadic fixations (p<.05). Fixations preceding up-directed saccades became significantly briefer when the flicker was in the UpVF compared to no distractor (p<.01). This asymmetry in pre-saccadic fixations for up- versus down-directed saccades adaptively allows irrelevant stimuli in the LoVF to be less distracting, and for potential threats in the UpVF to be attended to quicker.