Self-motion perception during conflicting visual-vestibular acceleration.

Self-motion is known to be falsely perceived during exposure to the movement of visual surroundings. This illusory perception of visually-induced self-motion is known as "vection." The present study was conducted to examine the relative strengths of vection versus whole-body angular acceleration as they determine perceived self-rotation under conditions in which they individually provide conflicting information. Each subject was rotated for 90 s about a vertical axis at a constant acceleration, and a large-field visual surround in front of the subject was simultaneously rotated at a constant acceleration in the same direction, but at a magnitude of acceleration twice that of the body. This stimulus condition creates a sensory conflict between information from the vestibular/somatosensory systems and information from the visual system with respect to the direction of self-rotation. The subject eventually perceived self-acceleration in the direction of circular vection (CV), even though he or she was actually being accelerated in the direction opposite to CV. When the magnitude of contradictory chair acceleration exceeded the vestibular perceptual threshold, the onset latency of CV was significantly delayed. Our results suggest that visual information contributes to the perception of self-acceleration, and that illusory self-motion could overwhelm the feeling of self-acceleration due to inertial motion. CV would thus be a significant factor in determining spatial orientation in certain operational environments and flight conditions.