Desmurget M, Prablanc C, Arzi M, Rossetti Y, Paulignan Y, Urquizar C
Institut National de la Santé et de la Recherche Médicale Unité 94, Bron, France.
Exp Brain Res. 1996 Jul;110(2):265-78. doi: 10.1007/BF00228557.
At a descriptive level, prehension movements can be partitioned into three components ensuring, respectively, the transport of the arm to the vicinity of the target, the orientation of the hand according to object tilt, and the grasp itself. Several authors have suggested that this analytic description may be an operational principle for the organization of the motor system. This hypothesis, called "visuomotor channels hypothesis," is in particular supported by experiments showing a parallelism between the reach and grasp components of prehension movements. The purpose of the present study was to determine whether or not the generalization of the visuomotor channels hypothesis, from its initial form, restricted to the grasp and transport components, to its actual form, including the reach orientation and grasp components, may be well founded. Six subjects were required to reach and grasp cylindrical objects presented at a given location, with different orientations. During the movements, object orientation was either kept constant (unperturbed trials) or modified at movement onset (perturbed trials). Results showed that both wrist path (sequence of positions that the hand follows in space), and wrist trajectory (time sequence of the successive positions of the hand) were strongly affected by object orientation and by the occurrence of perturbations. These observations suggested strongly that arm transport and hand orientation were neither planned nor controlled independently. The significant linear regressions observed, with respect to the time, between arm displacement (integral of the magnitude of the velocity vector) and forearm rotation also supported this view. Interestingly, hand orientation was not implemented at only the distal level, demonstrating that all the redundant degrees of freedom available were used by the motor system to achieve the task. The final configuration reached by the arm was very stable for a given final orientation of the object to grasp. In particular, when object tilt was suddenly modified at movement onset, the correction brought the upper limb into the same posture as that obtained when the object was initially presented along the final orientation reached after perturbation. Taken together, the results described in the present study suggest that arm transport and hand orientation do not constitute independent visuomotor channels. They also further suggest that prehension movements are programmed, from an initial configuration, to reach smoothly a final posture that corresponds to a given "location and orientation" as a whole.
在描述层面上，抓握动作可分为三个部分，分别确保手臂向目标附近移动、根据物体倾斜对手进行定向以及抓握动作本身。几位作者提出，这种分析性描述可能是运动系统组织的一种操作原则。这一假说，即“视觉运动通道假说”，尤其得到了一些实验的支持，这些实验表明抓握动作的伸展和抓握部分之间存在平行关系。本研究的目的是确定视觉运动通道假说从其最初形式（仅限于抓握和移动部分）推广到其实际形式（包括伸展定向和抓握部分）是否有充分依据。要求6名受试者伸手去抓握放置在给定位置、具有不同定向的圆柱形物体。在动作过程中，物体定向要么保持不变（未受干扰试验），要么在动作开始时改变（受干扰试验）。结果表明，手腕路径（手在空间中遵循的位置序列）和手腕轨迹（手连续位置的时间序列）都受到物体定向和干扰发生的强烈影响。这些观察结果有力地表明，手臂移动和手部定向并非独立规划或控制。观察到的手臂位移（速度矢量大小的积分）与前臂旋转之间关于时间的显著线性回归也支持这一观点。有趣的是，手部定向并非仅在远端层面实现，这表明运动系统利用了所有可用的冗余自由度来完成任务。对于要抓握的物体的给定最终定向，手臂最终达到的构型非常稳定。特别是，当在动作开始时物体倾斜突然改变时，校正使上肢进入与物体最初沿干扰后达到的最终定向呈现时相同的姿势。综上所述，本研究中描述的结果表明，手臂移动和手部定向并不构成独立的视觉运动通道。它们还进一步表明，抓握动作是从初始构型开始编程的，以便平稳地达到与给定的“位置和定向”整体相对应的最终姿势。
