Motor Control Hierarchy in Joint Action that Involves Bimanual Action

Abstract

The concept of hierarchical motor control has been viewed as a means of progressively decreasing the number of variables manipulated by each higher control level. We tested the hypothesis that turning an individual bimanual force production task into a joint (two-participant) force production task would lead to positive correlation between forces produced by the two hands of the individual participant (symmetric strategy) to enable negative correlation between forces produced by two participants (complementary strategy). This study consisted of individual and joint tasks that involved both unimanual and bimanual conditions. In the joint task, ten pairs of participants produced periodic isometric forces such that the sum of forces they produced matched a target force cycling between 5% and 10% of maximum voluntary contraction at 1 Hz. In the individual task, individuals attempted to match the same target force. In the joint bimanual condition, the two hands of each participant adopted a symmetric strategy of force whereas the two participants adopted a complementary strategy of force, highlighting that the bimanual action behaved as a low level of a hierarchy whereas the joint action behaved as an upper level. The complementary force production was greater interpersonally than intrapersonally. But, while the coherence was highest at 1 Hz in all conditions, the frequency synchrony was stronger intrapersonally than interpersonally. Moreover, while the bimanual action exhibited a smaller error and variability of force than the unimanual action, the joint action exhibited a less variable interval and force than the individual action.