Marotta J J, Medendorp W P, Crawford J D
Canadian Institutes of Health Research Group for Action and Perception, Department of Psychology, Centre for Vision Research, York University, Toronto, Ontario M3J-1P3, Canada.
J Neurophysiol. 2003 Dec;90(6):3816-27. doi: 10.1152/jn.00418.2003. Epub 2003 Aug 20.
The purpose of the current study was to investigate the contribution of upper and lower arm torsion to grasp orientation during a reaching and grasping movement. In particular, we examined how the visuomotor system deals with the conflicting demands of coordinating upper and lower arm torsion and maintaining Donders' Law of the upper arm (a behavioral restriction of the axes of arm rotation to a two-dimensional "surface"). In experiment 1, subjects reached out and grasped a target block that was presented in one of 19 orientations (5 degrees clockwise increments from horizontal to vertical) at one position in a vertical presentation board. In experiment 2, target blocks were presented in one of three orientations (horizontal, three-quarter, and vertical) at nine different positions in the presentation board. If reach and grasp commands control the proximal and distal arms separately, then one would only expect the lower arm to contribute to grasp orientations and that Donders' Law would hold for the upper arm-independent of grasp orientations. Instead, as the required grasp orientation increased from horizontal to vertical, there was a significant clockwise torsional rotation in the upper arm, which accounted for 9% of the final vertical grasp orientation, and the lower arm, which accounted for 42%. A linear relationship existed between the torsional rotations of the upper and lower arm, which indicates that the components of the arm rotate in coordination with one another. The location-dependent aspects of upper and lower arm torsion remained invariant, however, yielding consistently shaped Donders' "surfaces" (with different torsional offsets) for different grasp orientations. These observations suggest that the entire arm-hand system contributes to grasp orientation, and therefore, the reach/grasp distinction is not directly reflected in proximal-distal kinematics but is better reflected in the distinction between these coordinated orienting rules and the location-dependent kinematic rules for the upper arm that result in Donders' Law for one given grasp orientation.
本研究的目的是调查在伸手抓取动作过程中，上臂和下臂扭转对抓握方向的贡献。具体而言，我们研究了视觉运动系统如何应对协调上臂和下臂扭转以及维持上臂的东德斯定律（手臂旋转轴在二维“平面”上的行为限制）这两个相互冲突的需求。在实验1中，受试者伸手抓取一个目标方块，该目标方块以19种方向之一（从水平到垂直，顺时针每隔5度）呈现在垂直展示板的一个位置上。在实验2中，目标方块以三种方向之一（水平、四分之三、垂直）呈现在展示板的九个不同位置上。如果伸手和抓握指令分别控制近端和远端手臂，那么人们只会预期下臂对抓握方向有贡献，并且东德斯定律将适用于上臂——与抓握方向无关。相反，随着所需抓握方向从水平增加到垂直，上臂出现了显著的顺时针扭转旋转，占最终垂直抓握方向的9%，下臂占42%。上臂和下臂的扭转旋转之间存在线性关系，这表明手臂的各个部分相互协调旋转。然而，上臂和下臂扭转的位置相关方面保持不变，对于不同的抓握方向，产生了形状一致的东德斯“平面”（具有不同的扭转偏移）。这些观察结果表明，整个手臂 - 手部系统都对抓握方向有贡献，因此，伸手/抓握的区别并非直接反映在近端 - 远端运动学中，而是更好地反映在这些协调的定向规则与上臂的位置相关运动学规则之间的区别上，这些规则导致了针对一个给定抓握方向的东德斯定律。
