Execution of Complex Action Sequences Under Various Cognitive Demand With and Without Hand Biomechanics Alterations

Abstract

Many previous studies have investigated the effects of compromised limb biomechanics oncognitive-motor performance. However, many have focused on lower rather than upper extremities while disregarding problem-solving tasks achieved under various demands. Additionally, limited efforts have examined performance and mental workload concurrent to the completion of a complex sequential task utilizing upper extremities and particularly when their biomechanics are altered. However, the examination of cognitive-motor performance when upper limb biomechanics are compromised would inform the relationship between cognitive and sensorimotor control processes. This work aims to examine the effects of altered hand biomechanics on performance and mental workload as individuals solve a sequential task under two cognitive demands. In the current work, participants completed the Tower of Hanoi task under both low and high cognitive demand while the hand effector was biomechanically altered or not. Biomechanics alterations were achieved via a brace, in which degrees of freedom and effector sensorimotor capabilities were substantially diminished. The sequential task performance was examined via Levenshtein Distance (LD), which assesses the optimality of participant sequencing along with sequence completion time, which was subsequently segmented to measure time during which hand movement is being executed or paused, and the number of disk drops. Mental workload and physical demand were assessed via NASA-TLX survey, while visual analog scale surveys evaluated physical as well as cognitive effort and fatigue. Results revealed that compared to the unbraced condition, brace usage led to an increase of the hand motion time along with an elevation of both perceived mental workload as well as cognitive fatigue and effort without affecting the structure of the sequence (i.e., LD) nor the time during which movement was paused. The same findings were obtained in response to an elevation of cognitive task demands with the only difference being that of a deterioration of sequence structure (i.e., increased LD) and an elevation of the time during which movement was paused were also observed. Furthermore, enhanced cognitive task demand under the brace condition led to an elevation of the number of disk drops and perceived physical demand accompanied by an increase of physical effort and fatigue whereas this was not observed for the unbraced conditions. These findings suggest the alteration of the upper-extremity biomechanics, or an elevation of cognitive-task demand resulted in a decrement of performance along with an elevation of the engagement of cognitive-motor processing resources resulting in a greater mental workload and ultimately leading to a decrease of cognitive-motor efficiency. Further, an increase of cognitive task demand leading to greater errors of fine sensorimotor coordination (disk drops) while maintaining the action sequence structure when individuals performed with compromised but not normal limb biomechanics suggest that individuals may have prioritized the completion of the action sequencing at the expense of the accurate motor execution. In turn, these greater sensorimotor errors would have required further movement regulation leading to an increase of the perceived physical demand, effort and fatigue. This work provides further insight into the understanding of adaptive human behavior and has the potential to inform rehabilitation of individuals with compromised upper-extremity biomechanics.