Abstract
Tilt of stimulus in the wide visual field causes the sensation of body tilt, indicating that visual information affects the perceived orientation of gravity in addition to vestibular and somatosensory information. However, the details of the multi-sensory integration process for perceiving the gravitational vertical are not fully illustrated. The purpose of this study is to investigate the properties of the integration process for the perception of gravitational vertical. In the experiment, we manipulated the orientations of visual stimuli and subject's body about the roll axis, and collected data of perceived gravitational vertical. To tilt subject's body, we used a seat, which could rotate with subject's body locked on it. A LCD monitor with 30cm diameter aperture was placed in front of subject's head to present the pictures of landscapes as visual stimuli. There was a black disc in the center of the pictures and a line segment was placed in the disc. The subject aligned the segment to the orientation of perceived gravitational vertical using keypad in his hand. Results showed that visual information affected the perception of gravitational vertical systematically. When the orientation indicated by visual stimuli was close to the real gravitational vertical, perceived gravitational vertical approached to the vertical of visual stimuli. On the other hand, when the orientation indicated by visual stimuli was very different from gravitational vertical, the effect of the visual stimuli was not observed. Neither the weighted liner summation model nor the vector summation model fits to these results. We propose a new model of multi-sensory integration for the perception of gravitational vertical.