Task prioritization is an important factor affecting attention allocation during dual-tasks (e.g. walking while completing a cognitive task) and determines the magnitude and direction of dual-task interference in older adults. Greater dual-task cost during walking may lead to falling, sometimes causing lasting effects to mobility. We investigated dual-task interference for walking and cognitive performance. Twenty-two healthy, older adults (71 5years) completed three cognitive tasks: letter fluency, category fluency, and serial subtraction during seated and walking conditions on a self-paced treadmill for three minutes each, in addition to a walking only trial. Walking speed, step width and length, were measured during walking and each dual-task condition. Percentage of correct answers was greater for letter fluency than the other two cognitive tasks (p=0.021) across single- and dual-tasks. Step width was significantly wider during dual-task letter fluency compared to walking alone (p=0.001), category fluency (p=0.001), and serial subtraction (p=0.007). During both fluency tasks, there was a cost for gait and cognition, with category showing a slightly higher cognitive cost compared to letter fluency. During letter fluency, to maintain cognitive performance, gait was sacrificed by increasing step width, which showed more sensitivity to dual task related changes than two other gait measures. Conversely, during serial subtraction, there was a cost for gait, yet a benefit for cognitive performance. As demonstrated in this study, all three cognitive tasks lead to different dual-task interference. It is critical to understand that the type of cognitive task may have a differential effect on both cognitive and motor dual-task costs.
