A Motion Illusion Reveals Mechanisms of Perceptual Stabilization
Figure 3
Role of eye movements (Exp. 2).
A) Perceived peripheral motion varied with central patterns in both fixation conditions. The central pattern had a stronger effect in ‘poor’ (blank circle) than in ‘good’ (cross) fixation trials. B) Representative eye trajectory during pattern presentation. Four seconds (250 Hz sampling rate) of eye movements (horizontal and vertical) following pattern onset are shown. Horizontal (x) and vertical (y) eye positions were converted into instantaneous velocity vectors (shifts between two samples) and filtered by a 20 ms unweighted box-car filter. Subsequently, velocity vectors were transformed into polar vectors (direction and amplitude). Saccade periods (bold) were detected as described elsewhere [22] (see also Materials and Methods). C) ‘Poor’ fixation resulted in larger fixation instability (s.d. of instantaneous velocities of saccade-free drift periods) than ‘good’ fixation. Pattern arrangement (incongruent, neutral, and congruent) had no effect on eye movements. D) Time course of drift micromovements (fixation instability). Fixation instability was calculated for each of four consecutive time intervals (each one second) starting with pattern onset. Drift micromovements decreased between the 1st and 2nd and increased between the 3rd and 4th interval. Error bars reflect within-subjects standard errors of the mean.