Spatial reference and standing posture during high-speed Coriolis stimulation

BACKGROUND: In a previous study, we found that sensation, gaze, and posture during Coriolis stimulation differ considerably between vision and nonvision conditions during rotations at 60 degrees x s(-1). To determine the validity of these findings at higher velocities, we compared standing postures during Coriolis stimulation up to 150 degrees x s(-1) between vision and nonvision conditions. METHODS: The 19 subjects underwent 5-min rotation tests at 50 to 150 degrees x s(-1). While standing on a force platform attached to a rotating device, each subject tilted his or her head and then returned it to upright, first with the eyes covered, then with eyes open. Six subjects were re-examined 5 d later after 4 consecutive days of 20-min rotations with their eyes open. We assessed success and failure to stand and recorded the center of pressure during rotation. RESULTS: Although success rates (number of successes/19) differed between vision and nonvision conditions at 50 degrees x s(-1) (94.7% vs. 57.9%), they steeply decreased as rotation velocity increased and showed no difference at 70 degrees x s(-1) and faster velocities. After the 4-d exposure, however, subjects could stand at higher velocities particularly under the vision condition. A patient with bilateral labyrinthine loss, being examined for reference, could stand at 110 degrees x s(-1) even with the eyes covered. CONCLUSIONS: Untrained subjects frequently fell during high-speed Coriolis stimulation, apparently because vision was insufficient to provide a spatial reference frame from the stationary surroundings. Following rotation training with their eyes open, subjects appeared more able to use the visual reference frame and falls were reduced.