Speed Estimation of Vection Produced by Two Optical Flows at Different Speeds

Abstract

We investigated the vection (visually induced self-motion perception) that occurred when 2 optical flows expanded at different speeds in the same space. In the experiments, we set the difference in speed between 2 optical flows as the speed condition, and varied the ratio of the numbers of random dots composing the optical flows. Subjects estimated vection speed produced by 2 optical flows. The results showed that when the speed difference was small, the estimated vection speed varied linearly with the ratio of the random dots. When the speed difference was large and the 2 optical flows were perceived to be separate, the results were classified into 2 groups. In one group, vection speed tended to depend upon the slower optical flow, whereas in the other group, vection speed depended upon both optical flows. Even in the latter case, however, the slower optical flow contributed more to the vection speed. To explain these characteristics of vection speed, we developed a model in which vection speed was predicted by the summation of the speeds of 2 optical flows, weighted by the ratio of the random dots of each optical flow.