Integration of Visual, Vestibular and Somatosensory Information for the Perception of Gravitational Vertical and Forward Self-Motion

We investigated how human perceives forward self-motion from the information produced by the vestibular, somatosensory and visual systems. In the experiments, we manipulated vestibular and somatosensory information by changing the direction of the subject's body. The subject sat in a drum which was tilted about the pitch axis of the subject. We also manipulated the visual information by presenting optic flow of dots on the display in front of the subject. In Exp.1, the pitch of subject was fixed at a certain angle for each trial. In Exp.2, the pitch angle was changed temporally, and the acceleration of the optic flow was synchronized with the angle to simulate the flow produced by the forward self-motion of the acceleration. During the trials, the subject continuously responded the gravitational vertical. In the condition of fixed pitch angle (Exp.1), subjects' responses of the gravitational vertical almost corresponded to the real direction and were not affected by the visual stimulus. In the condition of changing pitch angle (Exp.2), the responses were close to the direction of their foot. These results suggest that, the temporal correspondence between vestibular, somatosensory and visual information is important for the perception of forward self-motion