Vection increases the magnitude and accuracy of visually evoked postural responses

Movement of large visual scenes induces an illusion of self-motion (vection) and postural responses. We investigated if the conscious perception of self-motion influences the magnitude and directional accuracy of visually evoked postural responses. Five normal subjects fixated the centre of a large disk rotating in the roll (coronal) plane. The disk was placed either in front of the subjects or obliquely 30 deg to their right or left; in these oblique positions disk fixation was achieved by horizontal ocular deviation alone (i.e. no neck deviation). Subjects indicated their subjective perceptual status, either vection or object motion, with a push button. The results confirmed that the direction of the visually evoked postural response was reoriented according to the different eye-disk positions. In addition, both the magnitude of the postural response and the accuracy of its alignment with the disk rotational plane were significantly increased during vection periods. The results show that conscious perception of self-motion enhances visuopostural performance. Since conscious perception is likely to arise at cortical levels, the findings indicate that the cortex is one of the sites where gaze direction interacts with retinal motion signals to provide a self-motion signal in body-centric co-ordinates. Such interaction provides a substrate for spatial representation during motion in the environment.