INSERM U405, Hopitaux Universitaires de Strasbourg, France.
Cogn Neuropsychol. 2000 Dec 1;17(8):731-59. doi: 10.1080/026432900750038317.
We examined whether an agnosic patient with a deficit in early visual processing, HJA, completed occluded contours. We used matching tasks with stimuli composed of three superimposed or occluded shapes. Experiments 2 and 6 required superimposed or occluded shapes to be discriminated from distractors in which the position of one shape was changed. HJA was selectively impaired with occluded relative to superimposed shapes. His performance was affected by the spatial separation of the occluded contours rather than the area of the occluded surface. Experiments 3 and 5 required HJA to discriminate the central shape. Making occluded contours easier to compute (by reducing their spatial separation) facilitated discrimination of a central occluded shape (in the background), although it impaired discrimination of a central occluding shape (in the foreground). Free-choice shape judgements made to the central shape (Experiment 2) showed that HJA used both real and completed contours to segment foreground shapes inappropriately. When asked to copy overlapping shapes (Experiment 4), HJA drew in the occluded parts as if real contours were present, at least on some occasions. These drawings and a task requiring discrimination between real and occluded contours (Experiment 7), showed a tendency to continue contours inappropriately, an insensitiviy to junctions, and impaired integration of contours into more global shapes. The results suggest that occluded contours can be computed early on in visual processing, probably at the level where long-range mechanisms group collinear contour segments together. Our control experiment shows that HJA is not impaired in collinear contour grouping. These mechanisms are prior to processes in which contours are bound to shapes and in which foregroundbackground relationships between shapes are resolved. In visual agnosia, occluded contours can be computed even when there is impairment of both binding of contours to shapes and the computation of foreground-background relations in overlapping shapes.
我们考察了一位在早期视觉加工方面存在缺陷的失认症患者 HJA 是否能完成对被遮挡轮廓的识别。我们使用匹配任务，其刺激由三个叠加或被遮挡的形状组成。实验 2 和 6 需要被叠加或被遮挡的形状与位置发生改变的干扰项区分开来。HJA 在被遮挡的形状相对于叠加的形状时表现出选择性损伤。他的表现受到被遮挡轮廓的空间分离的影响，而不是被遮挡表面的面积的影响。实验 3 和 5 需要 HJA 来识别中心形状。使被遮挡的轮廓更容易计算（通过减少它们的空间分离）有利于对中央被遮挡形状（在背景中）的识别，尽管它会损害对中央遮挡形状（在前景中）的识别。对中央形状进行的自由选择形状判断（实验 2）表明，HJA 使用真实和完成的轮廓来不恰当地分割前景形状。当被要求复制重叠的形状（实验 4）时，HJA 会在被遮挡的部分绘制轮廓，就好像真实的轮廓存在一样，至少在某些情况下是这样。这些图形和需要在真实轮廓和被遮挡轮廓之间进行区分的任务（实验 7）表明，HJA 存在不恰当地继续轮廓的倾向，对连接点不敏感，并且轮廓整合到更全局的形状的能力受损。这些结果表明，被遮挡的轮廓可以在视觉处理的早期阶段被计算出来，可能是在长程机制将共线轮廓段组合在一起的水平上。我们的对照实验表明，HJA 在共线轮廓分组方面没有受损。这些机制先于轮廓与形状绑定的过程，以及形状之间的前后关系得到解决的过程。在视觉失认症中，即使在轮廓与形状绑定和重叠形状中前背景关系的计算都受损的情况下，也可以计算被遮挡的轮廓。
