Robertson E M, Miall R C
University Laboratory of Physiology, Oxford, UK.
Exp Brain Res. 1997 Oct;117(1):148-52. doi: 10.1007/s002210050208.
The human arm is kinematically redundant, which may allow flexibility in the execution of reaching movements. We have compared reaching movements with and without kinematic redundancy to unpredictable double-step targets. Subjects sat in front of a digitising tablet and were able to view an arc of four targets reflected in the mirror as virtual images in the plane of the tablet. They were instructed to move, from a central starting point, in as straight a line as possible to a target. In one-third of trials, the target light switched to one of its neighbours during the movement. Subjects made 60 movements using shoulder, elbow and wrist and then another 60 movements in which only shoulder and elbow movement were allowed. By restraining the wrist, the limb was made non-redundant. The path length was calculated for each movement. In single-step trials, there was no significant difference between path lengths performed with and without wrist restraint. As expected there was a significant increase in path length during double-step trials. Moreover this increase was significantly greater when the wrist was restrained. The variability across both single- and double-step movements was significantly less while the wrist was restrained. Importantly the performance time of the movements did not alter significantly for single-step, double-step or restrained movements. These results suggest that the nervous system exploits the intrinsic redundancy of the limb when controlling voluntary movements and is therefore more effective at reprogramming movements to double-step targets.
人类手臂在运动学上是冗余的，这可能使伸手够物动作的执行具有灵活性。我们比较了对不可预测的双步目标进行伸手够物动作时，有和没有运动学冗余情况下的差异。受试者坐在数字化平板电脑前，能够在平板电脑平面上通过镜子将四个目标的弧线作为虚拟图像进行查看。他们被要求从中央起始点尽可能直线地移动到一个目标。在三分之一的试验中，目标光在运动过程中切换到其相邻目标之一。受试者先使用肩部、肘部和腕部进行60次动作，然后再进行60次动作，其中只允许肩部和肘部运动。通过限制腕部运动，使肢体变为非冗余状态。计算每次动作的路径长度。在单步试验中，有腕部限制和无腕部限制时执行的路径长度之间没有显著差异。正如预期的那样，在双步试验中路径长度显著增加。此外，当腕部受到限制时，这种增加更为显著。在腕部受到限制时，单步和双步动作的变异性均显著降低。重要的是，单步、双步或受限动作的执行时间没有显著改变。这些结果表明，神经系统在控制自主运动时利用了肢体固有的冗余性，因此在将动作重新编程以适应双步目标方面更有效。
