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Jonathan Matthis, Mary Hayhoe; The functional coupling of gaze and gait when walking over real-world rough terrain. Journal of Vision 2016;16(12):766. doi: 10.1167/16.12.766.
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© 2017 Association for Research in Vision and Ophthalmology.
When walking over rough terrain, walkers must gather information about the layout of the upcoming path to support stable and efficient locomotion. In this context, the biomechanics of human gait define the task constraints that organize eye movements when traversing difficult terrain. However, very little is known about gaze patterns while walking outside a laboratory setting. It seems likely that a walker's gaze will be heavily biased towards regions of upcoming terrain around their biomechanically-preferred foothold location, with temporal coupling to the phase of the ongoing gait cycle in a manner shaped by the physical dynamics of bipedal walking. To test this hypothesis, we developed a novel experimental apparatus that records the eye movements and full-body kinematics of subjects walking over real-world terrain. For the first time, we can precisely record gaze and body movement data during natural behavior in unconstrained outdoor environments. Subjects walked over terrain of three increasing difficulties –obstacle-free packed earth paths, moderately rocky trails, and extremely rough dry creekbeds. In flat terrain, subjects spent most of the time looking far down the path and visually exploring their environment. Ground fixations were infrequent and not directed towards future footholds, consistent with the minimal visual information needed to guide foot placement in flat terrain. In contrast, subjects walking over rough terrain displayed strong spatiotemporal coupling between gaze patterns on upcoming terrain and their ongoing gait cycle. In difficult terrain, subjects performed rapid visual search on regions around 2-4 steps ahead, often fixating precisely on locations of upcoming footholds. Saccades between future footholds suggest that nearby steps are selected by balancing between the biomechanically-preferred, energetically optimal step location and the availability of footholds further down the path. Thus the demands of foot placement in real-world terrain leads to more active and flexible gaze patterns than predicted from laboratory-based experiments.
Meeting abstract presented at VSS 2016
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