Cuijpers Raymond H, Smeets Jeroen B J, Brenner Eli
Department of Neuroscience, Erasmus MC, PO Box 1738, 3000 DR Rotterdam, The Netherlands.
J Neurophysiol. 2004 Jun;91(6):2598-606. doi: 10.1152/jn.00644.2003. Epub 2004 Jan 28.
Despite the many studies on the visual control of grasping, little is known about how and when small variations in shape affect grasping kinematics. In the present study we asked subjects to grasp elliptical cylinders that were placed 30 and 60 cm in front of them. The cylinders' aspect ratio was varied systematically between 0.4 and 1.6, and their orientation was varied in steps of 30 degrees. Subjects picked up all noncircular cylinders with a hand orientation that approximately coincided with one of the principal axes. The probability of selecting a given principal axis was the highest when its orientation was equal to the preferred orientation for picking up a circular cylinder at the same location. The maximum grip aperture was scaled to the length of the selected principal axis, but the maximum grip aperture was also larger when the length of the axis orthogonal to the grip axis was longer than that of the grip axis. The correlation between the grip aperture--or the hand orientation--at a given instant, and its final value, increased monotonically with the traversed distance. The final hand orientation could already be inferred from its value after 30% of the movement distance with a reliability that explains 50% of the variance. For the final grip aperture, this was only so after 80% of the movement distance. The results indicate that the perceived shape of the cylinder is used for selecting appropriate grasping locations before or early in the movement and that the grip aperture and orientation are gradually attuned to these locations during the movement.
尽管已有许多关于抓握视觉控制的研究，但对于形状的微小变化如何以及何时影响抓握运动学却知之甚少。在本研究中，我们要求受试者抓握放置在他们前方30厘米和60厘米处的椭圆圆柱体。圆柱体的纵横比在0.4至1.6之间系统地变化，其方向以30度为步长变化。受试者用大致与其中一个主轴重合的手部方向拿起所有非圆形圆柱体。当给定主轴的方向等于在同一位置拿起圆柱体的首选方向时，选择该主轴的概率最高。最大抓握孔径根据所选主轴的长度进行缩放，但当与抓握轴正交的轴的长度比抓握轴的长度更长时，最大抓握孔径也更大。在给定时刻的抓握孔径或手部方向与其最终值之间的相关性随着移动距离单调增加。在移动距离的30%之后，就可以从其值推断出最终的手部方向，其可靠性可以解释50%的方差。对于最终的抓握孔径，只有在移动距离的80%之后才可以这样推断。结果表明，圆柱体的感知形状用于在运动之前或运动早期选择合适的抓握位置，并且抓握孔径和方向在运动过程中逐渐调整到这些位置。
