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Jonathan Matthis, Sean Barton, Brett Fajen; The critical period for the visual control of foot placement in complex terrain occurs in the preceding step. Journal of Vision 2014;14(10):3. doi: 10.1167/14.10.3.
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© ARVO (1962-2015); The Authors (2016-present)
Successful locomotion over complex terrain such as a rocky trail requires walkers to place each step on a safe foothold with high spatiotemporal precision while also taking the future terrain into account. Matthis & Fajen (2013) demonstrated that two step lengths of visual look ahead is sufficient for humans to walk over complex terrain while exploiting the inverted-pendulum-like structure of bipedal gait as efficiently as they do with unrestricted vision. In a follow-up study, we showed that the accuracy of stepping onto a target was unaffected when the target became invisible at any point during the step to that target, but sharply declined when the target disappeared during the preceding step. Taken together, these findings suggest that there is a critical period for the visual control of the placement of each step that occurs during the preceding step. Here we present a study that tests this critical period hypothesis by examining subjects as they walk over a series of irregularly spaced virtual targets projected onto the floor by a LCD projector. Targets were only visible during specific phases of the gait cycle leading up to each target. Indeed, we found that there was a narrow window during the stance phase preceding the step to each target during which the target needed to be visible in order for subjects to accurately place each foot. Even a brief presentation of a target during this critical period yielded better performance than a longer presentation at a different phase of gait. Interestingly, stepping was marginally more accurate when targets were visible for longer than the predicted critical period, regardless of whether they appeared slightly sooner or disappeared slightly later. Given the increased difficulty of the experimental task, this result suggests that subjects' performance was affected by attentional factors in addition to biomechanical constraints.
Meeting abstract presented at VSS 2014
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