Marotta J J, Behrmann M, Goodale M A
Department of Psychology, University of Western Ontario, London, Canada.
Exp Brain Res. 1997 Aug;116(1):113-21. doi: 10.1007/pl00005731.
The present study tested the idea that the visuomotor systems mediating prehension do not have independent access to pictorial cues processed by perceptual mechanisms. Individuals with visual form agnosia, whose perceptual systems are compromised but who have intact visuomotor control, were examined to determine whether they could use pictorial scene cues to calibrate manual prehension when binocular information was removed. The removal of binocular cues produced considerable disruptions in size-constancy of grip aperture, which, combined with earlier observations in normal subjects, suggests that binocular cues are of primary importance in calibration of grasping. In the absence of binocular vision, normal subjects can use pictorial information, information that is severely compromised in individuals with visual form agnosia, to compute the distance (and thus the size) of the goal object. Thus, individuals with visual form agnosia must rely on a retinal image that remains uncalibrated, leading to inaccurate calibrations of grip aperture. The fact that these individuals scaled their grasp much less accurately under the monocular viewing condition, despite showing normal binocular grasping, suggests that pictorial cues to depth, which are presumably processed by mechanisms mediating our perception of objects and events in the world, can be accessed by visuomotor mechanisms only indirectly. These results, together with others, suggest that the visuomotor system 'prefers' to use binocular information and uses pictorial cues only as a last resort.
本研究验证了这样一种观点，即介导抓握动作的视觉运动系统无法独立获取由感知机制处理的图像线索。研究人员对患有视觉形式失认症的个体进行了检查，这些个体的感知系统受损，但视觉运动控制功能完好，目的是确定在去除双眼信息后，他们是否能够利用图像场景线索来校准手动抓握动作。去除双眼线索后，抓握孔径的大小恒常性出现了相当大的干扰，这与之前对正常受试者的观察结果相结合，表明双眼线索在抓握校准中至关重要。在没有双眼视觉的情况下，正常受试者可以利用图像信息（而患有视觉形式失认症的个体严重缺乏这种信息）来计算目标物体的距离（进而计算其大小）。因此，患有视觉形式失认症的个体必须依赖未经校准的视网膜图像，这导致抓握孔径的校准不准确。尽管这些个体在双眼抓握时表现正常，但在单眼观察条件下抓握动作的缩放准确性要低得多，这一事实表明，深度的图像线索（大概是由介导我们对世界中物体和事件感知的机制处理的）只能被视觉运动系统间接获取。这些结果以及其他结果表明，视觉运动系统“更喜欢”使用双眼信息，只有在万不得已时才使用图像线索。
