Vision: Does it really drive locomotor steering responses?
Turning on foot is controlled using a robust sequence of axial segment reorientation starting with the eyes and head, and followed by the trunk and feet. Recent evidence suggests that turning may represent a whole-body gaze shift which is driven by the oculomotor control system. We propose that the coordination of axial body segments during steering represents a robust preprogrammed postural synergy initiated by eye and head rotation in a new travel direction, and that release of the steering synergy is dependent on a horizontal eye saccade that redirects gaze to the new direction of travel. The purpose of this thesis was to test hypotheses related to whether vision is the driving force behind such orienting strategies as the steering synergy. Whole-body kinematics and gaze behaviour were recorded to study the effects of visually presented virtual turns on steering responses during a stepping in place task. In support of our hypothesis, anticipatory eye, head, and body redirection revealed a sequenced order and timing of segment rotation that is characteristic of steering behaviour in real world turning situations. In addition, we observed that gaze fixation on a stationary target resulted in suppression of anticipatory steering responses. These results indicate that gaze redirection ' is' a prerequisite for the initiation of steering behaviour and that the release of the steering synergy is intimately linked to an oculomotor component. These observations further support the hypothesis that a coordinated whole body response is driven by the visual control system. The information obtained through this dissertation expands our current knowledge of how vision is used in the control of locomotion.