The dual task of memorizing word lists while walking was predicted to become more difficult with age because balance and gait are in greater need of "attentional resources." Forty-seven young (ages 20-30 years), 45 middle-aged (40-50), and 48 old (60-70) adults were trained to criterion in a mnemonic technique and instructed to walk quickly and accurately on 2 narrow tracks of different path complexity. Then, participants encoded the word lists while sitting, standing, or walking on either

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... ; likewise, speed and accuracy of walking performance were assessed with and without concurrent memory encoding. Dual-task costs increased with age in both domains; relative to young adults, the effect size of the overall increase was 0.98 standard deviation units for middle-aged and 1.47 standard deviation units for old adults. It is argued that sensory and motor aspects of behavior are increasingly in need of cognitive control with advancing age. The main purpose of this study was to test the prediction that the simultaneous execution of a challenging locomotion task-walking on a narrow track-and a memory task-memorizing a list of words-becomes increasingly difficult with advancing age. This prediction was motivated by the hypothesis that sensorimotor performance is increasingly in need of "attentional resources" ). As an illustration, imagine 20-yearold and 70-year-old pedestrians crossing a lively street corner. Because of losses in motor and sensory functioning, 70-year-old individuals will need, on average, to exert more attention to successfully perform this task than will 20-year-old individuals. As a consequence, one may hypothesize that they will be more likely than young adults to interrupt a conversation with another person while crossing the street. In addition, we thank Werner Scholtysik for his expert help in setting up the walking track; Matthias Stroux and Manfred Weilandt for programming assistance; Annette Rentz-Luhning, Daniela Jopp, Ulrike Bar, Mike Kortsch, Tania Singer, and Manfred Weilandt for data collection; and the research participants for their willingness to participate in a demanding study.