Saling M, Stelmach G E, Mescheriakov S, Berger M
Motor Control Laboratory, Arizona State University, Tempe 85287-0404, USA.
Behav Brain Res. 1996 Oct;80(1-2):153-60. doi: 10.1016/0166-4328(96)00030-7.
For prehensile tasks, where objects are located beyond the normal reaching space, the trunk is bent forward to assist in the transport of the wrist to the object. Such task behaviors raise complex motor control issues such as how is the trunk movement incorporated into the motor plan. In this experiment, seated subjects were asked to reach and grasp a small and a large object placed on a table located beyond their maximal reach. Forward trunk bending was required to extend the reach distance. For such reaching movements, the wrist velocity consisted of a bell shape profile similar to those seen when the arm is the sole transport agent. In most trials, the trunk was the first to initiate movement, although there was no strict pattern of initiation order. The transport data showed that trunk and arm movement components were decoupled at the end of the reach. While the object was being grasped and lifted, the trunk continued moving for approximately 180 ms after the grasp. Wrist deceleration time expressed in absolute and relative values was sensitive to object size. The time from maximum peak aperture to the end of wrist movement also was significantly longer for grasping the small compared to the large object. No such relationships were observed for the trunk. Temporal coupling was only observed between the grip and wrist transport component. Time to maximum aperture was significantly correlated with time to peak wrist deceleration and only rarely with time to trunk deceleration peak. When the trunk participates in the transport of the wrist to an object, these findings suggest that only the wrist component is directly related to the achievement of the grasp. While the trunk assisted the arm to reach the object, the kinematic parameter recorded did not reveal any evidence of direct coupling. The presented data suggests that the planning takes place at the level of the hand and that endpoint is the primary variable controlled.
对于需要抓握的任务，当物体位于正常够取空间之外时，躯干会向前弯曲，以协助将手腕移动到物体处。此类任务行为引发了复杂的运动控制问题，比如躯干运动如何融入运动计划。在本实验中，要求就座的受试者够取并抓握放置在超出其最大够取范围的桌子上的一个小物体和一个大物体。需要向前弯曲躯干来延长够取距离。对于此类够取动作，手腕速度呈现出钟形曲线，类似于仅用手臂作为唯一移动器官时所观察到的情况。在大多数试验中，躯干是最先开始移动的，不过启动顺序并没有严格的模式。运动数据表明，在够取动作结束时，躯干和手臂的运动部分是解耦的。在抓握并提起物体时，抓握动作完成后躯干还会继续移动约180毫秒。以绝对值和相对值表示的手腕减速时间对物体大小很敏感。与抓握大物体相比，抓握小物体时从最大开口峰值到手腕运动结束的时间也显著更长。在躯干方面未观察到此类关系。仅在抓握和手腕移动部分之间观察到了时间耦合。达到最大开口的时间与手腕减速峰值时间显著相关，而与躯干减速峰值时间仅有很少的相关性。当躯干参与将手腕移动到物体处时，这些发现表明只有手腕部分与抓握的完成直接相关。虽然躯干协助手臂够到物体，但所记录的运动学参数并未显示出任何直接耦合的证据。所呈现的数据表明，计划是在手部层面进行的，并且终点是主要的受控变量。
