Peripheral visual information influences head posture during gravitoinertial changes

International audienceThis study aimed at determining the effect of peripheral visual information on head posture during gravitoinertial changes induced by rotation. Subjects (N = 8), seated off-center on a rotating platform, were rotated in the frontal plane at 120degrees.s(-1) in the dark. Their trunk was fixed with respect to the chair but their head was free to move. Subjects were rotated in 7 conditions. In one (DARK condition), rotation occurred without any visual cues. In the six other conditions, subjects were facing three types of peripheral visual information: i) a fixed vertical frame, ii) a frame which orientation tilted with the gravitoinertial vector, and iii) a frame which orientation tilted opposite to the gravitoinertial vector. The visual frame was either switched on at the rotation onset or at constant velocity. Observations show that during the acceleration phase of the DARK condition, subjects' head progressively rotated toward the axis of rotation. Once at constant velocity, the head reached approximately 10degrees in roll and in yaw. Head was then not aligned with the gravitoinertial vector (17.3degrees) even after prolonged rotation in the dark. There is some evidence that head posture was the result of the counteraction of two antagonistic reflexes: the vestibulo-collic reflex which tends to align head with gravitoinertial forces and the cervico-collic reflex which tends to keep the head aligned with the trunk. When visual information was available, we observed a frame effect on head posture: subjects tended to reorientate their head towards the tilted visual frame. The frame affected head posture whatever its direction relative to the gravitoinertial vector. This postural response occurred when the frame appeared at the rotation onset or at constant velocity. It is concluded that visual information mediates the action of vestibulo-collic and cervico-collic reflexes on head posture