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Dorothy Cowie, Janette Atkinson, Oliver Braddick; Visual control representations in locomotion: stair descent in adults and children. Journal of Vision 2007;7(9):1020. doi: 10.1167/7.9.1020.
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© ARVO (1962-2015); The Authors (2016-present)
The use of visual information in controlling the detailed kinematics of manual actions has been extensively investigated. However, much less is known about the visual control of locomotor actions, in particular the demanding task of descending steps.
We have collected lower limb kinematic data during a ‘one-step’ task, in adults and 3–4 year old children. Using a single, variable-height step means that any dependence on step height must be mediated by visual information. Each participant was tested in three conditions: normal vision, blindfold, and ‘open-loop’. In ‘open-loop’, after a 2-second viewing period participants had an auditory cue to close their eyes and step down immediately. For each condition we collected data with three step heights, set as 8%, 16%, and 24% of the participant's leg length.
Adult data with normal vision showed that flexion of the lead leg, anticipating contact with the lower step, occurred at a depth which scaled with step height. When blindfold, flexion position was independent of step height, confirming that the scaling reflected the use of visual control information. 3–4 year olds showed a similar scaling, suggesting that the use of such information in stair descent is remarkably mature at this age.
In the open-loop condition, adults scaled their leg movements to step height almost as well as with normal vision. This implies that stair descent does not depend on continuous on-line control, but on a visual control representation which persists at least briefly after visual information is removed. Evidence for a similar capability in the 3–4 year olds' data will be discussed.
Our findings provide a paradigm for extending current theories of action-perception systems into the locomotor domain. They suggest, for example, that the distinction between ‘perception’, ‘planning’ and ‘control’ (Glover, 2004) may be a useful one to apply to locomotor development.
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