Santello M, Soechting J F
Department of Physiology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Neurophysiol. 1998 Mar;79(3):1307-20. doi: 10.1152/jn.1998.79.3.1307.
Subjects were asked to reach to and to grasp 15 similarly sized objects with the four fingers opposed to the thumb. The objects' contours differed: some presented a concave surface to the fingers, others a flat one, and yet others a convex surface. Flexion/extension at the metacarpal-phalangeal and proximal interphalangeal joints of the fingers was recorded during the reaching movement. We used discriminant analysis, cluster analysis, and information theory to determine the extent to which the shape of the hand was affected by the objects' shapes along a convexity/concavity gradient. Maximum aperture of the hand was reached about midway in the reaching movement. At that time, the hand's posture was influenced by the shape of the object to be grasped but imperfectly. The information transmitted by hand posture about object shape increased gradually and monotonically as the hand approached the object, reaching a maximum at the time the object was in the grasp of the hand. We also asked subjects to shape the hand so as to grasp the object without moving the arm. Their performance was poorer on this task in the sense that hand shape discriminated among fewer objects and that trial-to-trial variability was greater than when the distal and proximal components of the motion were linked. The results indicate that the hand is molded only gradually to the contours of an object to be grasped. Because other parameters of the motion, such as movement direction, for example, already are specified fully early on in a movement, the results also suggest that the specification of diverse aspects of a movement does not evolve at a uniform rate.
受试者被要求用与拇指相对的四指去够取并抓握15个大小相似的物体。物体的轮廓各不相同：有些物体表面呈凹面，有些呈平面，还有些呈凸面。在伸手够取动作过程中，记录手指掌指关节和近端指间关节的屈伸情况。我们运用判别分析、聚类分析和信息论来确定手部形状在凸度/凹度梯度上受物体形状影响的程度。手部的最大张度大约在伸手够取动作的中途达到。此时，手部姿势受待抓握物体形状的影响，但并不完全。随着手部靠近物体，手部姿势传递的关于物体形状的信息逐渐且单调增加，在物体被手部抓握时达到最大值。我们还要求受试者在不移动手臂的情况下塑造手部形状以抓握物体。在这项任务中，他们的表现较差，因为手部形状能区分的物体较少，而且每次试验之间的变异性比运动的远端和近端部分相连时更大。结果表明，手部只是逐渐适应待抓握物体的轮廓。由于运动的其他参数，比如运动方向，在运动早期就已完全确定，结果还表明，运动不同方面的确定并非以统一速率发展。
