Abstract
Vection is the illusion of making observers feel as though they are in motion when they are not through the use of moving visual stimuli. We studied circular vection by situating stationary adults in an optokinetic drum (2m diameter) with black and white stripes each subtending an angle of approximately 20 degrees that rotated at a constant speed of 5 rpm. In all previous studies that we know about, the subjects were centered in such a drum and so the visual flow specified a simple rotation in place. And other studies investigated sensitivity to simple translations while subjects stood in place within a rectangular room that translated to and fro. In our three experiments subjects stood off-center in an optokinetic drum. In these situations the visual input specified self-movements that were simple rotations, or the translations combined with rotations that would occur when one walks around the perimeter of an optokinetic drum. Five viewing positions were used: the center and positions near the optokinetic drum's curtain located behind, in front of, left of, and right of center. This is one of the first studies to compare judgments of the perception of vection for simple rotations with vection for rotations combined with translations. The results showed highly significant effects of viewing position, indicating large differences in latencies for perceiving simple rotations compared with perceiving curved paths.