Rossetti Y, Meckler C, Prablanc C
Vision and Motricité, INSERM U. 94, Bron, France.
Exp Brain Res. 1994;99(1):131-6. doi: 10.1007/BF00241417.
Processing of joint redundancy is one of the most important problems in motor control. For instance, gaze orientation can be obtained with an infinite number of eye and head combinations. It has been proposed that a solution to this problem might be the minimization of eye and head position-signal errors. For arm movements, where the excess of degrees of freedom is even higher, cost function was proposed as a criterion for movement selection, reflecting some comfort variable evoked from the peripheral inputs, e.g. optimal muscular energy cost or glucose consumption. However, no biological implication of comfort on motor control has yet been demonstrated. We have further investigated this approach by hypothesizing that arm posture choice also relies on a minimization of position-signal errors arising from individual joints. The prediction is that accuracy of fingertip localization by pointing made by the contralateral hand would be enhanced for comfortable postures of the target arm and degraded for uncomfortable postures using extreme joint positions. Results show an increase in pointing variability when extreme joint postures are used (wrist flexion, shoulder elevation, or both). This increase in pointing variability is proportional to the increase in subjective discomfort rating. Individual joint effects can be added arithmetically into a whole arm value for both discomfort rating and pointing variable and constant error. These results suggest that the choice of comfortable postures for the arm corresponds to an optimization of arm position-signal reliability. This new constraint might be a useful tool for further investigation on posture or trajectory formation.
关节冗余度的处理是运动控制中最重要的问题之一。例如，通过无数种眼睛和头部的组合都可以获得注视方向。有人提出，解决这个问题的一个办法可能是使眼睛和头部位置信号误差最小化。对于手臂运动，其自由度冗余度更高，人们提出用代价函数作为运动选择的标准，该函数反映了从外周输入中引发的一些舒适度变量，例如最佳肌肉能量消耗或葡萄糖消耗。然而，舒适度对运动控制的生物学意义尚未得到证实。我们通过假设手臂姿势的选择也依赖于使各个关节产生的位置信号误差最小化，进一步研究了这种方法。预测结果是，对于目标手臂的舒适姿势，对侧手进行指向时指尖定位的准确性会提高，而对于使用极端关节位置的不舒适姿势，指尖定位的准确性会降低。结果表明，当使用极端关节姿势（手腕弯曲、肩部抬高或两者皆有）时，指向的变异性会增加。这种指向变异性的增加与主观不适感评分的增加成正比。对于不适感评分以及指向变量和恒定误差，各个关节的影响可以算术相加得到整个手臂的值。这些结果表明，选择手臂的舒适姿势对应于手臂位置信号可靠性的优化。这个新的约束条件可能是进一步研究姿势或轨迹形成的有用工具。
