Sudden movement of platform and postural stability

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When a bus begins to move, a standing person in the car continues upright posture using so-called postural response. What kind of information provokes this response? This question has not been answered yet. The purpose of this paper is to research the correlation between postural response and vestibular information. In this research, we developed the new device to stimulate a subject in forward-backward direction or right-left direction. A gist of possible stimulations by this device are as following.a) Velocity of platform : 50, 100, 200, 300 mm/seconds.b) Distance of platform movement : 10, 50, 100, 150 mmc) Time for constant velocity : 50, 200 millisecondsd) Two kinds of moving : one way, go and backThe subject stands on the stabilometry equipped on the platform of this apparatus and being attached sensor of the acceleration on left side of his head. Postural response and postural sway was evaluated by moving of center of foot pressure. These recorded data were taken into computer with 100 Hz of data sampling rate and analyzed. Eight subjects were examined. Each subject showed head acceleration just after the platform's starting. The latency of this head acceleration was constant instead of variability of directions and velocity of stimulations. On the other hands, the latency of postural responses was shortened in proportion to increase of acceleration of stimulation. From these results, this head acceleration observed in this stimulation seemed not to be a trigger of postural response.