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Multitask performance in adaptive gait: structural and capacity interference
In community mobility, walking is commonly completed with other concurrent tasks, described as locomotor multitasks. Many locomotor multitasks rely on vision for both gait and concurrent tasks. When each of the individual tasks uses the same perceptual modality (e.g. vision), structural interference occurs. Structural interference is different from capacity interference, which refers to tasks competing for limited cognitive resources. While locomotor multitask studies have demonstrated that completing the locomotor multitask typically leads to performance impairment in gait and/or the concurrent task, the wide range of tasks has confounded the ability to fully understand how structural and capacity interference affect multitask performance. Thus, the purpose of this dissertation was to delineate how structural interference (Study 1) and capacity interference (Study 2) affect gait multitask performance. To facilitate comparison across studies, the two studies (Study 1 and Study 2) in this dissertation used the same gait task – obstacle crossing – and the same cognitive task – a visual discrete reaction time (RT) task. A discrete RT task was completed while approaching to an obstacle, where visual information regarding obstacle is being gathered to plan for the successful obstacle crossing. In Study 1, to determine if structural interference affects performance impairment in young and older adults, gaze diversion was manipulated by the RT task location (gaze diverted to the obstacle, and gaze diverted away from the obstacle). The RT task was also completed while standing to strengthen the interpretation that any performance impairments were due to structural interference. Study 1 results indicated that structural interference affects both gait and cognitive task performance. Structural interference demonstrated performance impairments in both young and older adults, but the strategies were different. Young adults were more likely adopt gait behavior that increased the risk of tripping when gaze was diverted away from the obstacle (high structural interference), but older adults demonstrated a strategy that decreased the risk of trip when gaze was diverted to the obstacle (low structural interference). This finding highlights the critical role of vision in adaptive gait. In study 2, to determine if capacity interference affects performance impairment in young adults, both gait and cognitive task were manipulated while structural interference was held constant; gait task was manipulated by obstacle height (level walking, 15% leg length height, and 30% leg length height obstacle), and cognitive tasks were three RT tasks (Simple RT, Choice RT, Simon RT). The baseline for each gait task (without RT task) and cognitive task (while seating) was also measured. Capacity interference demonstrated that task prioritization strategy was different for gait challenge versus cognitive challenge in young adults. As gait task difficulty increased, gait task was prioritized. Conversely, as cognitive task difficulty increased, cognitive task was prioritized. This finding highlights that young adults have the ability to flexibly allocate the resources to accomplish the multitask. Lastly, an interesting finding from two studies (Study 1 and Study 2) was when interference is applied during the planning phase – during the approach to the obstacle – structural interference has a greater effect on obstacle crossing performance than capacity interference.