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Sean Barton, Jonathan Matthis, Evelyn Hinojosa, Dylan Brion, Brett Fajen; Biomechanical and visual constraints on rapid adjustments to foot placement during continuous locomotion. Journal of Vision 2016;16(12):767. doi: https://doi.org/10.1167/16.12.767.
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To control precise stepping onto a target foothold, walkers use visual information prior to step initiation to modify the ballistic trajectory of the body (Matthis, Barton, & Fajen, 2015). This allows them to capitalize on the energetic efficiency and stability afforded by the pendular structure of the lower limbs. However, it is often necessary to respond to changes in the position of intended target footholds that occur around step initiation. If walkers use visual information to modify their ballistic trajectory in response to perturbations, changes in the trajectory of the center of mass (COM) should be apparent and should occur early in the step. Alternatively, if vision is used to actively guide the foot in a reach-like movement, responses should be localized to the foot and occur later. Twelve subjects walked over a path of lighted foot targets while their movements were recorded by a motion capture system. On some trials, the location of one target in the path was perturbed in one of four directions either before or after step initiation. Analyses of acceleration profiles of the feet and COM revealed that the response depended on both the time and direction of perturbation. When perturbations occurred along the direction of locomotion, changes in COM acceleration were observed early in the gait cycle if visual information was available during the preceding step or near toe-off. Perturbations orthogonal to the direction of locomotion elicited reach-like movements of the foot later in the step, regardless of whether the perturbation occurred before or after step initiation. Walkers use visual information to exploit their pendular structure even when responding to perturbations, but this is dependent on the timing of the perturbation relative to step initiation. Additionally, walkers make reach-like movements with the foot when adapting the ballistic trajectory is untenable.
Meeting abstract presented at VSS 2016
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