Control of steering in the presence of unexpected head yaw movements. Influence on sequencing of subtasks.
Control of the head during locomotion has been suggested as a means of facilitating overall postural control of the body. The control of online steering is challenging, as it requires the central nervous system (CNS) to simultaneously control body reorientation in a new direction while modifying the ongoing step cycle. Stable body posture during steering is maintained via appropriately organized postural responses to error signals detected by the visual, vestibular, and/or proprioceptive systems. Modifications to the gait cycle include step-width regulation and movement of body center of mass (COM) in the direction of travel, and may be preceded by independent control of head orientation to see where one is going. The purpose of this investigation was to examine how the ability to successfully steer is influenced by unexpected head perturbations and how various body segments are coordinated and controlled to successfully steer along different pathways. Body kinematics were monitored as participants changed their direction of travel by varying amounts when visually cued one stride before the turn. Perturbations to the head were applied to either assist or oppose the change in direction one step prior to initiation of the turn. Analyses focused on the timing of the changes in head yaw, trunk yaw, and COM trajectories in the mediolateral plane. Results indicate that the order of control over the body segments was head and trunk reorientation in the direction of travel and finally movement of the COM in the intended direction. Thus gaze, inferred from head movement, preceded changes in COM trajectory. This suggests that looking where you are going is critical for steering. When steering is potentially compromised by unexpected head movements, the CNS delays committing movement of the COM until it has a chance to look at the new travel path.
Vallis
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Gait and Posture Lab, Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
Patla
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Adkin
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D000328:Adult; D001696:Biomechanical Phenomena; D001921:Brain / Q000502:physiology*; D003463:Cues; D005260:Female; D005684:Gait / Q000502:physiology; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008027:Light; D008124:Locomotion / Q000502:physiology*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D009862:Online Systems; D009949:Orientation / Q000502:physiology*; D010775:Photic Stimulation; D011187:Posture; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time