Effect of Contradiction between Visual and Vestibular Information on the Human Postural Control Characteristics

The effect of contradiction between the visual and the vestibular information on the human postural control has been analyzed by means of the artificial alteration to the visual feedback information. To give the stereoscopic vision depending upon the motion of the test subject's head to his eyes, the three dimensional visor display system has been developed, This system can separate the visual information about the head motion into the rotational and the translational components and alter them independently of each other by changing the corresponding display gains. In the first experiment, the test subjects stood upright and carried out the tracking tasks by using their head rotation in different combinations of the display gain, The body sway increased more in amplitude in the case where the reversed component of the rotational head motion was displayed than in the case where the component was not displayed. This means that it is more important for the postural control system to maintain the consistent relationship between the visual and the vestibular information rather than to acquire the amount of the feedback information. In the second experiment, the increase in the display gain of the rotational component increased the body sway more in amplitude than that of the translational component. It can be guessed that this phenomenon is related to a psychological constancy that the display gain with respect to the rotational component of the head motion is primarily unchangeable.