Influence of heading perception in the control of posture.

The optic flow visual input directly influences the postural control. The aim of the present study was to examine the relationship between visually induced heading perception and postural stability, using optic flow stimulation. The dots were accelerated to simulate a heading direction to the left or to the right of the vertical midline. The participants were instructed to indicate the perceived optic flow direction by making a saccade to the simulated heading direction. We simultaneously acquired electromyographyc and center of pressure (COP) signals. We analysed the postural sway during three different epochs: (i) the first 500 ms after the stimulus onset, (ii) 500 ms before saccade onset, epoch in which the perception is achieved and, (iii) 500 ms after saccade onset. Participants exhibited a greater postural instability before the saccade, when the perception of heading was achieved, and the sway increased further after the saccade. These results indicate that the conscious representation of the self-motion affects the neural control of posture more than the mere visual motion, producing more instability when visual signals are contrasting with eye movements. It could be that part of these effects are due to the interactions between gaze shift and optic flow.