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Aftab E. Patla and Anne Shumway-Cook

Mobility, the ability to move independently, is critical to maintaining independence and quality of life. Among older adults, mobility disability results when an individual cannot meet the demands of the environment. Current approaches to defining mobility rely on distance and time measures, or decompose mobility into subtasks (e.g., climbing, sit to stand), but provide limited understanding of mobility in the elderly. In this paper, a new conceptual framework identifies the critical environmental factors, or dimensions, that operationally define mobility within a given community, such as ambient conditions (light levels, weather conditions) and terrain characteristics (stairs, curbs). Our premise is that the environment and the individual conjointly determine mobility disability. Mobility in the elderly is defined not by the number of tasks a person can or cannot perform, but by the range of environmental contexts in which tasks can be safely carried out: the more disabled, the more restrictive the dimensions.

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Luiz C. Santos, Renato Moraes, and Aftab E. Patla

The purpose of the current study was to understand how visual information about an ongoing change in obstacle size is used during obstacle avoidance for both lead and trail limbs. Participants were required to walk in a dark room and to step over an obstacle edged with a special tape visible in the dark. The obstacle’s dimensions were manipulated one step before obstacle clearance by increasing or decreasing its size. Two increasing and two decreasing obstacle conditions were combined with seven control static conditions. Results showed that information about the obstacle’s size was acquired and used to modulate trail limb trajectory, but had no effect on lead limb trajectory. The adaptive step was influenced by the time available to acquire and process visual information. In conclusion, visual information about obstacle size acquired during lead limb crossing was used in a feedforward manner to modulate trail limb trajectory.