Axis of visual field rotation and order of presentation differentially affect postural responses in a virtual environment

We employed a virtual environment to examine the effect of a visual field rotating about the interaural or talo-crural axes on postural behaviors in 11 healthy young adults. Subjects stood quietly in the dark or while the virtual scene rotated in upward pitch on a platform that tilted the ankle into dorsiflexion. Three orders of visual axis rotation were presented. Greater body sway occurred with visual field rotations about the head than the ankle. Ankle muscle activity increased in all visual rotation orders, but the relative response to the head and ankle axis visual rotations depended upon the order of presentation. We conclude that visual field motion combined with a support surface disturbance increases system excitability, and that rotations of the visual field about the axis of the head are more disturbing to upright posture than rotations about the ankle.