Domkin Dmitry, Laczko Jozsef, Jaric Slobodan, Johansson Hakan, Latash Mark L
Centre for Musculo-Skeletal Research, National Institute for Working Life, Box 7654, 907 13 Umea, Sweden.
Exp Brain Res. 2002 Mar;143(1):11-23. doi: 10.1007/s00221-001-0944-1. Epub 2001 Dec 11.
Changes in the structure of motor variability during practicing a bimanual pointing task were investigated using the framework of the uncontrolled manifold (UCM) hypothesis. The subjects performed fast and accurate planar movements with both arms, one moving the pointer and the other moving the target. The UCM hypothesis predicts that joint kinematic variability will be structured to selectively stabilize important task variables. This prediction was tested with respect to selective stabilization of the trajectory of the endpoint of each arm (unimanual control hypotheses) and with respect to selective stabilization of the timecourse of the vectorial distance between the target and the pointer tip (bimanual control hypothesis). Components of joint position variance not affecting and affecting a mean value of a selected variable were computed at each 10% of normalized movement time. The ratio of these two components ( R(V)) served as a quantitative index of selective stabilization. Both unimanual control hypotheses and the bimanual control hypothesis were supported both prior to and after practice. However, the R(V) values for the bimanual control hypothesis were significantly higher than for either of the unimanual control hypothesis, suggesting that the bimanual synergy was not simply a simultaneous execution of two unimanual synergies. After practice, an improvement in both movement speed and accuracy was accompanied by counterintuitive changes in the structure of kinematic variability. Components of joint position variance affecting and not affecting a mean value of a selected variable decreased, but there was a significantly larger drop in the latter when applied on each of the three selected task variables corresponding to the three control hypotheses. We conclude that the UCM hypothesis allows quantitative assessment of the degree of stabilization of selected performance variables and provides information on changes in the structure of a multijoint synergy that may not be reflected in its overall performance.
运用非受控流形（UCM）假说框架，研究了在进行双手指向任务练习过程中运动变异性结构的变化。受试者用双臂进行快速且准确的平面运动，一只手臂移动指针，另一只手臂移动目标。UCM假说预测，关节运动学变异性将被构建以选择性地稳定重要任务变量。针对各手臂端点轨迹的选择性稳定（单臂控制假说）以及目标与指针尖端之间矢量距离的时间进程的选择性稳定（双臂控制假说），对这一预测进行了检验。在归一化运动时间的每10%处，计算不影响和影响所选变量平均值的关节位置方差分量。这两个分量的比值（R(V)）作为选择性稳定的定量指标。单臂控制假说和双臂控制假说在练习前后均得到了支持。然而，双臂控制假说的R(V)值显著高于任何一个单臂控制假说，这表明双臂协同并非简单地是两个单臂协同的同时执行。练习后，运动速度和准确性的提高伴随着运动学变异性结构的反直觉变化。影响和不影响所选变量平均值的关节位置方差分量均下降，但在应用于对应三个控制假说的三个所选任务变量中的每一个时，后者下降幅度明显更大。我们得出结论，UCM假说允许对所选性能变量的稳定程度进行定量评估，并提供关于多关节协同结构变化的信息，而这些变化可能不会在其整体性能中体现出来。
