Khan Aarlenne Z, Pisella Laure, Rossetti Yves, Vighetto Alain, Crawford J Douglas
Centre for Vision Research, CIHR Group for Action and Perception and Department of Psychology, York University, Toronto, Ontario, Canada, M3J 1P3.
Cereb Cortex. 2005 Oct;15(10):1547-60. doi: 10.1093/cercor/bhi033. Epub 2005 Mar 2.
Recent studies have suggested that internal updating of visuospatial targets in humans occurs in gaze-centered coordinates and takes place in the parietal and extrastriate cortices. We explored how information for reaching is updated in two patients with bilateral lesions in these areas. Subjects performed two visuomotor tasks: (i) a fixation reaching task, which began with the appearance of one of five fixation positions (varying eye positions) followed by a central reaching target. Subjects reached to the target while fixating on the presented fixation position (relative to gaze the target was always presented in the periphery); and (ii) a saccade reaching task, in which subjects foveated on the central reaching target, then made a saccade to the presented fixation position before reaching to the central target. In both tasks, subjects reached to targets after a 500 or 5000 ms delay. Gaze-centered updating predicts similarities in reaching errors between fixation and saccade trials. Control subjects showed evidence for gaze-centered updating during both 500 and 5000 ms delay conditions. In contrast, patient AT, who had extensive occipital-parietal damage, only showed signs of gaze-centered representation after 5 s. Patient IG, with a more focal lesion in the parietal cortices, showed partial updating in gaze-centered coordinates when reaching with the small memory delay but recovered a complete gaze-centered representation after the longer delay. This suggests that patients with bilateral occipital-parietal lesions may rely on non-gaze-centered frames to store immediate target locations in reaching space but, given enough time, this information may be rerouted to access other gaze-centered motor cortical mechanisms.
最近的研究表明，人类视觉空间目标的内部更新是以注视为中心的坐标进行的，并且发生在顶叶和纹外皮层。我们探究了在这两个区域有双侧损伤的两名患者中，用于伸手够物的信息是如何更新的。受试者执行了两项视觉运动任务：（i）固定注视伸手任务，开始时会出现五个固定位置之一（不同的眼位），随后是一个中央伸手目标。受试者在注视呈现的固定位置时伸手够向目标（相对于注视，目标总是呈现在周边）；以及（ii）扫视伸手任务，受试者先注视中央伸手目标，然后在伸手够向中央目标之前扫视到呈现的固定位置。在这两项任务中，受试者在延迟500或5000毫秒后伸手够向目标。以注视为中心的更新预测了固定注视和扫视试验之间伸手误差的相似性。对照受试者在500和5000毫秒延迟条件下均显示出以注视为中心的更新证据。相比之下，患有广泛枕叶 - 顶叶损伤的患者AT，仅在5秒后才显示出以注视为中心的表征迹象。患有顶叶皮层更局灶性损伤的患者IG，在短记忆延迟伸手时在以注视为中心的坐标中显示出部分更新，但在更长延迟后恢复了完整的以注视为中心的表征。这表明双侧枕叶 - 顶叶损伤的患者可能依赖非以注视为中心的框架来存储伸手空间中即时目标位置，但给予足够时间后，该信息可能会重新路由以接入其他以注视为中心的运动皮层机制。
