Cuijpers Raymond H, Brenner Eli, Smeets Jeroen B J
Erasmus MC, Rotterdam, The Netherlands.
Exp Brain Res. 2006 Oct;175(1):32-44. doi: 10.1007/s00221-006-0531-6. Epub 2006 May 30.
There are many conditions in which the visually perceived shape of an object differs from its true shape. We here show that one can reveal such errors by studying grasping. Nine subjects were asked to grasp and lift elliptical cylinders that were placed vertically at eye height. We varied the cylinder's aspect ratios, orientations about the vertical axis and distances from the subject. We found that the subjects' grip orientations deviated systematically from the orientations that would give the mechanically optimal grip. That this is largely due to misjudging the cylinder's shape (rather than to selecting a comfortable posture) follows from the fact that the grip aperture was initially more strongly correlated with the maximal grip aperture (which is related to the expected contact positions) than with the final grip aperture (which is determined by the real contact positions). The correlation with the maximal grip aperture drops from 0.8 to 0.6 in the last 1% of the traversed distance (11% of movement time), showing that the grip aperture was anticipated incorrectly (it is automatically "corrected" at contact). The grip orientation was already strongly correlated with the grip orientation at the time of maximal grip aperture, half way through the movement (R > or = 0.7), showing that the suboptimal grip orientations were planned that way. We conclude that subjects plan their grasps using information that is based on the misperceived shape.
在许多情况下，物体的视觉感知形状与其真实形状不同。我们在此表明，通过研究抓握动作可以揭示这种误差。九名受试者被要求抓握并提起垂直放置在眼睛高度的椭圆圆柱体。我们改变了圆柱体的纵横比、绕垂直轴的方向以及与受试者的距离。我们发现，受试者的抓握方向系统地偏离了能给出机械最优抓握的方向。这很大程度上是由于对圆柱体形状的误判（而非选择舒适姿势），这一结论源于以下事实：抓握孔径最初与最大抓握孔径（与预期接触位置相关）的相关性比与最终抓握孔径（由实际接触位置决定）更强。在移动距离的最后1%（移动时间的11%）内，与最大抓握孔径的相关性从0.8降至0.6，这表明抓握孔径被错误预估（在接触时会自动“校正”）。抓握方向在移动到一半、达到最大抓握孔径时就已经与当时的抓握方向高度相关（R≥0.7），这表明次优抓握方向就是这样被规划的。我们得出结论，受试者基于误判的形状信息来规划他们的抓握动作。
