Abstract
Observers viewed random-dot optical flow displays that simulated self-motion on a circular path and judged whether they would pass to the right or left of a target at 16 m. Two dots in 2 frames are theoretically sufficient to specify circular heading if the orientation of the rotation axis is known. Heading accuracies were better than 1.5° with a ground surface, wall surface, and 3-dimensional cloud of dots and were constant over densities down to 2 dots, consistent with the theory. However, there was an inverse relation between the radius of the observer's path and constant heading error, such that at small radii observers reported heading 3° to the outside of the actual path with the ground and to the inside with the wall and cloud. This may be an artifact of a small display screen.