Abstract
Ankle joint stiffness was measured while visual stimulation was applied to quietly standing ten healthy subjects using head-mounted display (HMD). The presented image consists of eight horizontal stripes moving up and down in 8 and 32 seconds cycle, with and without a fixed (non-moving) point display. The measured ankle joint stiffness during the visual stimulation with a fixed point showed the intermediate value between the eyes-open and the eyes-closed conditions, while the visual stimulation without a fixed point induced the larger stiffness as expected. The less stiffness due to the fixed point than eyes-closed condition was confirmed in other nine healthy subjects with the same visual stimulation protocol but at 4, 8, 16 and 32 seconds cycle. The trajectory length of the center-of-pressure was also measured on the same subjects. The better postural stability than eyes-closed condition was confirmed in the both methods. It was hypothesized that the position error between the actual gaze point and the presented fixed point was induced by vestibular reflex, and the subject detected the postural information from that error. The head position and electro-oculogram was measured in five subjects wearing HMD and vestibular reflex was observed. It was revealed that gazing a point improves the postural stability presumably by contribution of vestibular reflex, even in a case gazing point does not provide position information such as HMD environment.
