Gaze strategies in peripheral motion detection: On the superiority of fixations over smooth pursuit eye movements (SPEM)

Peripheral-motion-change-detection performance was examined by contrasting a fixation with a SPEM condition. To that end, participants were confronted with a visual display consisting of 15 white squares and 1 red square circulating with 6°/s (tracking condition) and stopping in-between (fixation condition). The instruction was to visually follow the red square and to press a button as soon as a white square begins to move. The to-be-detected white square movements varied in eccentricity and speed. A Vicon-integrated eye-tracking system was used for controlling gaze behaviour. Response times (ms) and missed detections (%) were measured as dependent variables. Results in Experiment 1 show faster motion-change detection in fixation vs. tracking condition (401 ms vs. 809 ms) and increased response times as a function of eccentricity in the tracking condition only (4°: 570 ms; 8°: 737 ms; 16°: 1121 ms). Moreover, missed detections were revealed at 16° eccentricity in the tracking condition only. Experiment 2 controlled for foveal load as possible confounder by replacing the red square with a virtual centre evoked by 4 red squares. The same results were obtained as in Experiment 1. In sum, it could be shown that SPEM impair the ability to detect peripheral motion changes.