Dual-task performance in older adults during discrete gait perturbation.

The dual-task (motor and cognitive) performance of eight older adults (72.0 ± 6.4 years; 5 female; 3 male) was evaluated. Vocal choice reaction times (cognitive task) were measured at standstill as well as during unperturbed and perturbed gait (motor task). The perturbation was administered using customized shoes instrumented to lower a small (18.4 mm high) aluminum flap suddenly under the medial or lateral forefoot during a single swing phase of 12 of 30 gait trials. The ankle inverted or everted an average of 10 or 9 degrees, respectively, depending on the flap deployed. Medial and lateral perturbations were randomized between the left and right feet. The results show that vocal choice reaction time was significantly prolonged by gait, both perturbed (614.7 ± 80.2 ms) and unperturbed (529.9 ± 119.3 ms), compared to standstill (332.8 ± 76.5 ms; p = 0.0015). Further, the prolongation associated with gait perturbation was significant, compared to that with unperturbed gait (p = 0.016). The kinematics of the first post-perturbation (recovery) step, with or without concomitant vocal choice reaction task performance, was not significantly different from those of the average step during unperturbed gait. We conclude that in healthy older adults, the requirement to respond to a gait challenge resulted in deterioration in the performance of a concurrent cognitive task as indicated by significant prolongation of response time in the vocal choice reaction task. In contrast, performance of the motor task was not adversely affected.