The aim of this study was to examine the validity of a 2-choice audio-vocal reaction time (RT) probe task for measuring the changes in attentional demand during practice and learning of a discrete motor task. Twenty participants practiced the motor task across 3 days and were probed with the RT task during either the preparation or execution phase of the primary task. As practice progressed, participants improved in the primary task performance and shortened the RTs to the probe task. This indicated that less attention was required to plan and execute the movement and suggested that the RT probe task was a sensitive and valid tool to measure changes in attentional demands across practice. The authors implemented several additional experimental controls to address possible confounders including unintentional learning of the probe task, primary-secondary task trade-off effects, and compliance with task priority instructions. These experimental controls further ensured the validity of the probe paradigm and interpretability of the dual-task cost findings. Our experimental methods provided confirmatory evidence for the validity of the 2-choice RT task as a means to assess attentional demands during motor learning.
This study investigated the muscle activity and force variability in response to perturbation of assistive force during isometric elbow flexion. Sixteen healthy right-handed young men (age: 22.0 ± 1.1 years; height: 171.9 ± 4.8 cm; weight 68.4 ± 11.2 kg) were recruited and the muscle activity of biceps brachii and triceps brachii were assessed using surface electromyography. Workload force and assistive force applied on isometric elbow flexion significantly affected the changes in both biceps and triceps muscle activities. A higher assistive force was shown to result in reduced biceps muscle activity compared to the unassisted period. In contrast, the efficiency of the assistive force acting on the biceps decreased as the assistive force increased. In general, the force variability of the biceps muscle remained approximately the same at lower workload force conditions than that at higher workload force conditions. In conclusion, higher assistive force may not yield a higher performance efficiency in human-assistive force interaction.