Probing attention prioritization during dual-task step initiation: a novel method.

The present study investigated the attention allocation during reactive stepping using a continuous finger-tapping task. Ten healthy young subjects were recruited to participate in this study. Subjects were required to perform a rapid voluntary step with either left or right leg after hearing an auditory tone while tapping their right index finger on a handhold numeric keypad. Step initiation conditions included simple and choice reaction forward stepping with three variants of continuous tapping task that were: (1) single task--no concurrent finger-tapping task; (2) dual task easy--one-button tapping task; (3) dual task hard--four-button tapping task. Types of anticipatory postural adjustment (APA) were determined by the center of pressure trajectory. Reaction time, APA duration, and stepping latency were compared between APA types and various dual-task conditions. Wavelet analysis was performed on the stimulus-locked finger-tapping data to determine the frequency change of tapping speed related to reactive stepping. Results showed that postural performance was negatively affected only by the high-attention-demanding cognitive task. Significant reduction of finger-tapping speed post-stimulus presentation was observed across all test conditions, indicating attention shift during the execution of a step. In addition, the DTH condition induced early postural prioritization in choice reaction stepping when different motor programs needed to be planned and executed. Error APA also triggered larger deterioration of tapping performance compared to correct APA, indicating the perceived error and the remedial action require additional attentional resources.