Adaptation to bimanual asymmetric weights in isometric force coordination.

This study examined how different weighting coefficients imposed on individual finger force regulate bimanual finger force coordination patterns under the influence of bilateral coupling and visual information of the force output. The weighted sum of the two forces was computed as the total force output to match two target force levels (10% and 35% MVC) in separate conditions, and visual feedback of the total force output was provided in the experiment. The results revealed higher performance error at 35% in comparison with 10% MVC with the greatest error at the unequal coefficient setting. The correlation between the individual forces and the force output ratios correlated nonlinearly with the weighting coefficient ratios; however, the extent of change was much smaller than the coefficient ratios. The results suggest that bilateral coupling and task constraints interact to determine the coordination strategy. The irregularity of the individual finger forces increased with the weighting coefficient while the irregularity of the total force remained the same. The results support the hypothesis that the organization of redundant motor coordination patterns emerges from the interactive effect of the constraints on movement.