Abstract
Self-motion perception typically involves inputs from the visual and vestibular systems. Usually these inputs are in agreement, but when illusory self-motion (vection) occurs, they often conflict. Environments that yield vection include vehicle simulators, virtual reality, and optokinetic drums. Under optokinetic drum conditions, a stationary observer views the patterned interior of a large rotating cylinder and vection is typically experienced within 30 seconds. Why the delay in vection onset? Consider that the vestibular system responds to changes in velocity and direction. Some investigators have suggested that the latency period represents the time it would take for the semi-circular canal fluid to settle. An experiment was conducted using an optokinetic drum containing six pairs of black and white vertical stripes that rotated at 5RPM. In the same direction condition, vection was measured as the drum rotated clockwise for 30 sec. After a 5-sec period of eyes closed, vection was measured for an additional 30 sec with the drum moving in the same direction. In the different direction condition the first 30 sec period was identical, but during the second 30 sec period the drum moved counterclockwise. Results: mean vection onset latencies were significantly faster during the second half of each trial in both the same and different direction conditions. That vection onset was faster in the second half of the same direction condition supports the “fluid settling” hypothesis. However, this hypothesis is at odds with the result that vection onset is also faster for the second half of the different direction condition. If rotation direction suddenly changed, one would expect a longer period for visual and vestibular inputs to become aligned. It seems that vision's influence on vection persists for a time even if the observer's eyes are closed. How these results relate to motion sickness and sensory conflict will be addressed.
Supported by National Science Foundation Grant BCS-0002620