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Jonathan Matthis, Brett Fajen; Visual control of foot placement when walking over rough terrain. Journal of Vision 2011;11(11):915. doi: 10.1167/11.11.915.
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When people walk over rough terrain with obstacles to step over and irregularly spaced safe footholds, they must carefully choose their footsteps in a way that allows for forward progression while maintaining dynamic stability and minimizing energetic costs. The role of continuously available visual information when stepping over a single obstacle or onto a single target has been investigated in previous studies. When stepping over multiple obstacles, however, proper foot placement depends not only on the next obstacle but also on the size, position, and orientation of future obstacles. The goal of the present study was to investigate how far ahead along the future path visual information is needed to control foot placement. We developed a novel experimental paradigm in which subjects walked over an array of randomly distributed virtual obstacles that were projected onto the floor by a LCD projector while their movements were recorded using a full-body motion capture system. In the control condition, the entire array of obstacles was visible to subjects as they walked the length of the path. In other conditions, obstacles did not appear until they fell within a window of visibility centered on the subject's head. The size of the moving window was manipulated across blocks of trials. Walking behavior in each condition was compared to the control condition to estimate how far ahead along the upcoming path people need to see to avoid stepping on obstacles and to maintain forward progression and dynamic stability. Several measures of walking performance were computed, including walking speed, number of collisions, and the margin of dynamic stability. Data from three subjects show a strong effect of viewing distance on measures of walking performance, suggesting that visual information from several steps ahead is used to control foot placement when walking over rough terrain.
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