Kentridge R W, Heywood C A, Weiskrantz L
Department of Psychology, University of Durham, Durham DH1 3LE, United Kingdom.
Proc Natl Acad Sci U S A. 2007 Sep 18;104(38):15129-31. doi: 10.1073/pnas.0706603104. Epub 2007 Sep 6.
Color constancy refers to the unchanging nature of the perceived color of an object despite considerable variation in the wavelength composition of the light illuminating it. The color contrasts between objects and their backgrounds play a crucial role in color constancy. We tested a patient whose right striate cortex had been removed and demonstrated that he made no use of color contrast in judging color appearance but instead made judgments based simply on wavelength comparison. This was shown by presenting pairs of colored stimuli against a background color that gradually changed across space. When presented with such displays, both normal observers and those with cerebral achromatopsia (cortical color blindness) judge the color appearance of such stimuli on the basis of the chromatic contrast the stimuli make against their background rather than on the physical wavelengths of the light emitted from them. However, our patient made no such use of color contrast but, instead, made color discriminations simply on the basis of wavelength composition. This is consistent with recent findings from monkey electrophysiology that identify cells in early cortical visual areas that signal local contrast and so contribute to the likely mechanism for achieving color constancy.
颜色恒常性是指尽管照亮物体的光的波长组成有很大变化，但物体的感知颜色仍保持不变的特性。物体与其背景之间的颜色对比在颜色恒常性中起着至关重要的作用。我们测试了一位右侧纹状皮层已被切除的患者，结果表明他在判断颜色外观时并未利用颜色对比，而是仅仅基于波长比较来做出判断。这是通过在一个背景颜色在空间上逐渐变化的情况下呈现成对的彩色刺激来证明的。当呈现这样的显示时，正常观察者和患有脑性全色盲（皮质色盲）的人都是根据刺激与其背景形成的色相对比来判断此类刺激的颜色外观，而不是根据它们发出的光的物理波长。然而，我们的患者并未利用这种颜色对比，而是仅仅根据波长组成来进行颜色辨别。这与最近猴子电生理学的研究结果一致，该研究确定了早期皮质视觉区域中发出局部对比信号的细胞，这些细胞可能有助于实现颜色恒常性的机制。
