Effects of visual field on perceived speed of self-motion from optic flow

We investigated effects of visual field on perceived speed of self-motion from optic flow in two experiments. The optic flow patterns were produced as if an observer moved through a cylindrical volume (3m in radius) of which surface was filled with random dots. Observers compared perceived self-speed with the test stimulus to that with the stimulus presented on a full screen by twoalternative forced-choice staircase algorithm. In experiment 1 the test stimulus was curtailed radially to examine the effects of stimulus area. The results showed that the perceived self-speed increased with stimulus area. In experiment 2 the stimulus was curtailed concentrically to examine the interactions between stimulus area and retinal position. The results showed that the perceived self-speed increased with average of retinal image velocity. We suggest that perceived self-speed from optic flow is affected by 2-D factors, stimulus area and retinal distribution and that distance perception error may elicit different self-speed as a function of retinal eccentricity.