Merigan W H, Pham H A
Department of Ophthalmology and Center for Visual Science, University of Rochester Medical Center, NY 14642, USA.
Vis Neurosci. 1998 Mar-Apr;15(2):359-67. doi: 10.1017/s0952523898152112.
The role of cortical area V4 in complex shape discriminations was studied by testing the effects of V4 lesions in macaques on the ability to visually discriminate between images of three-dimensional (3D) objects from different viewpoints. Stimuli were presented in pairs in the lower left or lower right visual field quadrants about 4 deg from the fovea, and the monkeys judged on each trial whether the two views were of the same or of different objects. Object similarity was varied to determine a threshold shape difference. V4 lesions caused profound, retinotopic, and apparently permanent disruptions of discrimination, regardless of whether the images represented single or multiple viewpoints. In V4 lesioned portions of the visual field, monkeys could discriminate objects only when they differed much more grossly in shape than was true in control locations. These effects of the lesion were virtually identical for discriminations that had been learned before lesions were placed and for those learned afterwards. As in previous studies, V4 lesions elevated contrast thresholds by approximately a factor of two, but control observations showed that this was not the basis of the disruption of shape discrimination. Manipulation of cues to shape showed that in control locations, monkeys maintained excellent shape discrimination despite a variety of stimulus alterations, whereas in V4 lesioned areas their performance was easily disrupted. This finding suggests that V4 may support visual shape discriminations by facilitating the use of multiple visual cues. However, the fact that single-viewpoint and multiple-viewpoint discriminations were similarly affected indicates that the disruption was not specific to 3D shape discrimination, but may apply to a variety of subtle discriminations.
通过测试猕猴V4区损伤对从不同视角视觉辨别三维（3D）物体图像能力的影响，研究了皮质V4区在复杂形状辨别中的作用。刺激物成对呈现在距中央凹约4度的左下或右下视野象限，猴子在每次试验中判断这两个视图是同一物体还是不同物体的视图。改变物体相似度以确定形状差异阈值。无论图像代表单视角还是多视角，V4区损伤都会导致辨别能力出现严重的、视网膜拓扑性的且显然是永久性的破坏。在视野的V4区损伤部分，猴子只有在物体形状差异比对照部位大得多时才能辨别物体。损伤对损伤前已学会的辨别和损伤后学会的辨别产生的影响几乎相同。与之前的研究一样，V4区损伤使对比度阈值提高了约两倍，但对照观察表明这不是形状辨别破坏的基础。对形状线索的操控表明，在对照部位，尽管刺激有多种变化，猴子仍能保持出色的形状辨别能力，而在V4区损伤区域，它们的表现很容易受到干扰。这一发现表明，V4区可能通过促进多种视觉线索的使用来支持视觉形状辨别。然而，单视角和多视角辨别受到类似影响这一事实表明，这种破坏并非3D形状辨别所特有，可能适用于各种细微的辨别。
