Humphrey G K, Goodale M A, Corbetta M, Aglioti S
Department of Psychology, University of Western Ontario, London, Canada.
Curr Biol. 1995 May 1;5(5):545-51. doi: 10.1016/s0960-9822(95)00107-2.
The McCollough effect is a colour after-effect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns--such as a red-and-black vertical grating and a green-and-black horizontal grating--are viewed alternatively for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else.
Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90 degrees differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns.
These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.
麦考勒效应是一种颜色后效，它取决于用于诱发该效应的图案的方向。为了产生这种效应，交替观看两种方向不同的光栅图案，比如红色和黑色的垂直光栅以及绿色和黑色的水平光栅，持续几分钟。在这段适应期之后，如果以与适应图案相同的方向观看黑白测试光栅，垂直光栅的白色部分会呈现淡绿色，水平光栅的白色部分会呈现粉红色。麦考勒效应表明，颜色编码和方向编码机制在视觉处理的某个阶段相互作用；但问题仍然是这种相互作用是发生在皮层视觉通路的早期还是晚期。为了回答这个问题，我们研究了一位大脑纹外视觉区域遭受广泛损伤的患者，他虽然还能看见颜色，但其他方面几乎看不见了。
神经心理学和知觉测试表明，患者P.B.在形状感知方面有严重缺陷，甚至无法区分光栅刺激方向90度的差异。他也无法利用方向信息来控制伸手或抓握动作。然而，P.B.能够可靠地说出并区分不同颜色，包括用于诱发麦考勒效应的颜色。在用红色和绿色光栅进行适应之后，P.B.能够正确报告方向依赖的后效颜色，尽管他仍然无法区分测试图案的方向。
这些结果表明，在P.B.的视觉系统的某个层面上，方向正在被编码，但这个层面是他在进行方向判断或视觉运动控制时无法利用的。鉴于P.B.的纹外皮层受到了严重损伤，麦考勒效应背后机制的解剖学位置很可能在初级视觉皮层内，甚至在视觉通路中更早的位置。
