Backscroll illusion in far peripheral vision

The backscroll illusion refers to the apparent motion perceived in the background of a movie image that presents a locomotive object such as a person, an animal, or a vehicle. Here, we report that the backscroll illusion can occur in far peripheral visual fields at retinal eccentricity of more than 30 degrees. In psychological experiments, we presented a walking person in profile against an ambiguously moving background of vertical counterphase grating. This stimulus, which subtended 30 degrees of visual angle in width and height, was projected onto a hemispheric screen and positioned at horizontal eccentricity between 0 degrees and 50 degrees at intervals of 10 degrees. The eccentricity was changed randomly trial by trial, and stimulus duration was as short as 350 ms so that observers could not effectively move their eyes to the stimulus. Six observers viewed the stimulus either monocularly or binocularly and reported their perceptual impression for the grating in a three-alternative forced-choice procedure: drifting left, drifting right, or flickering. Results showed that the grating appeared to move in the opposite direction of walking at high probabilities even in the far periphery. Additional experiments confirmed that walking action could be recognized from the far peripheral stimulation. Our findings suggest that the visual system uses high-level object-centered motion signals to disambiguate retinal motion signals in the whole visual field.