Department of Kinesiology, The Pennsylvania State University, Rec.Hall-267, University Park, PA 16802, USA.
Exp Brain Res. 2010 Apr;202(1):213-29. doi: 10.1007/s00221-009-2128-3. Epub 2009 Dec 23.
We used the framework of the equilibrium-point hypothesis (in its updated form based on the notion of referent configuration) to investigate the multi-digit synergies at two levels of a hypothetical hierarchy involved in prehensile actions. Synergies were analyzed at the thumb-virtual finger (VF) level (VF is an imaginary digit with the mechanical action equivalent to that of the four actual fingers) and at the individual finger level. The subjects performed very quick vertical movements of a handle into a target. A load could be attached off-center to provide a pronation or supination torque. In a few trials, the handle was unexpectedly fixed to the table and the digits slipped off the sensors. In such trials, the hand stopped at a higher vertical position and rotated into pronation or supination depending on the expected torque. The aperture showed non-monotonic changes with a large, fast decrease and further increase, ending up with a smaller distance between the thumb and the fingers as compared to unperturbed trials. Multi-digit synergies were quantified using indices of co-variation between digit forces and moments of force across unperturbed trials. Prior to the lifting action, high synergy indices were observed at the individual finger level while modest indices were observed at the thumb-VF level. During the lifting action, the synergies at the individual finger level disappeared while the synergy indices became higher at the thumb-VF level. The results support the basic premise that, within a given task, setting a referent configuration may be described with a few referent values of variables that influence the equilibrium state, to which the system is attracted. Moreover, the referent configuration hypothesis can help interpret the data related to the trade-off between synergies at different hierarchical levels.
我们使用平衡态假说（基于参考构型概念的更新形式）的框架来研究参与抓握动作的两个层次的多自由度协同作用。协同作用在拇指-虚拟手指（VF）水平（VF 是一个想象中的手指，其机械作用等效于四个实际手指的作用）和单个手指水平上进行分析。受试者进行非常快速的手柄垂直运动到目标中。可以在非中心位置附加负载以提供旋前或旋后扭矩。在少数试验中，手柄意外固定在桌子上，手指从传感器上滑下。在这种试验中，手会停在更高的垂直位置，并根据预期的扭矩旋转到旋前或旋后。开口度表现出非单调变化，快速大幅减小，然后进一步增加，与未受干扰的试验相比，拇指和手指之间的距离较小。多自由度协同作用使用未受干扰试验中手指力和力矩之间的变异系数指数来量化。在提升动作之前，单个手指水平上观察到高协同作用指数，而拇指-VF 水平上观察到适度的指数。在提升动作期间，单个手指水平上的协同作用消失，而拇指-VF 水平上的协同作用指数变得更高。结果支持了一个基本前提，即在给定任务中，设置参考构型可以用几个影响平衡状态的变量的参考值来描述，系统会被吸引到这个状态。此外，参考构型假说可以帮助解释与不同层次协同作用之间权衡相关的数据。
