Dijkerman H C, Milner A D, Carey D P
School of Psychology, University of St. Andrews, St. Andrews, Scotland KY16 9JU.
Conscious Cogn. 1998 Sep;7(3):424-37. doi: 10.1006/ccog.1998.0365.
The cortical visual mechanisms involved in processing spatial relationships remain subject to debate. According to one current view, the "dorsal stream" of visual areas, emanating from primary visual cortex and culminating in the posterior parietal cortex, mediates this aspect of visual processing. More recently, others have argued that while the dorsal stream provides egocentric coding of visual location for motor control, the separate "ventral" stream is needed for allocentric spatial coding. We have assessed the visual form agnosic patient DF, whose lesion mainly affects the ventral stream, on a prehension task requiring allocentric spatial coding. She was presented with transparent circular disks. Each disk had circular holes cut in it. DF was asked to reach out and grasp the disk by placing her fingers through the holes. The disks either had three holes (for forefinger, middle finger, and thumb) or two holes (for forefinger and thumb). The distance between the forefinger and thumb holes, and the orientation of the line formed by them, were independently varied. DF was quite unable to adjust her grip aperture or her hand orientation in the three-hole task. Although she was able to orient her hand appropriately for the two-hole disks, she still remained unable to adjust her grip aperture to the distance between the holes. These findings are consistent with the idea that allocentric processing of spatial information requires a functioning ventral stream, even when the information is being used to guide a motor response.
参与处理空间关系的皮质视觉机制仍存在争议。根据目前的一种观点，从初级视觉皮层发出并在后顶叶皮层达到顶峰的视觉区域“背侧流”介导了视觉处理的这一方面。最近，其他人认为，虽然背侧流为运动控制提供视觉位置的自我中心编码，但异体中心空间编码需要单独的“腹侧”流。我们对视觉形式失认症患者DF进行了评估，她的损伤主要影响腹侧流，评估任务是一项需要异体中心空间编码的抓握任务。给她呈现透明圆盘。每个圆盘上都有圆形孔洞。要求DF伸出手，通过将手指穿过孔洞来抓住圆盘。圆盘要么有三个孔洞（用于食指、中指和拇指），要么有两个孔洞（用于食指和拇指）。食指和拇指孔洞之间的距离以及它们形成的线的方向是独立变化的。在三孔洞任务中，DF完全无法调整她的握力孔径或手部方向。尽管她能够将手正确地朝向双孔洞圆盘，但她仍然无法根据孔洞之间的距离调整握力孔径。这些发现与以下观点一致，即空间信息的异体中心处理需要一个正常运作的腹侧流，即使该信息用于指导运动反应。
