We investigated dual-task performance of cognitive (semantic fluency) and sensorimotor tasks (walking) in 120 children and adults from four age groups (9-year olds, M=9.52 years; 11-year olds, M=11.51 years; young adults, M=25.34 years; older adults, M=64.28 years; N=30 per group). Distances walked during 90 s and numbers of category exemplars generated in the semantic fluency task showed an inverted U-shape function with age. In line with general resource models proportional dual-task costs in walking also showed a U-shaped relation as a function of age with pronounced decrements in the youngest and oldest groups. Only 9-year olds showed significant costs in the cognitive task. Individual differences in single-task performance accounted for more than half of the variance in dual-task performance. Reliable age-related residual variance implicated additional factors particularly in children's developing multi-tasking performances.
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