Kusunoki Makoto, Moutoussis Konstantinos, Zeki Semir
Wellcome Laboratory of Neurobiology, University College London, London WC1E 6BT, UK.
J Neurophysiol. 2006 May;95(5):3047-59. doi: 10.1152/jn.00597.2005.
When objects are viewed in different illuminants, their color does not change or changes little in spite of significant changes in the wavelength composition of the light reflected from them. In previous studies, we have addressed the physiology underlying this color constancy by recording from cells in areas V1, V2, and V4 of the anesthetized monkey. Truly color-coded cells, ones that respond to a patch of a given color irrespective of the wavelength composition of the light reflected from it, were only found in area V4. In the present study, we have used a different approach to test the responses of V4 cells in both anesthetized and awake behaving monkeys. Stimuli of different colors, embedded within a Mondrian-type multicolored background, were used to identify the chromatic selectivity of neurons. The illumination of the background was then varied, and the tuning of V4 neurons was tested again for each background illumination. With anesthetized monkeys, the psychophysical effect of changing background illumination was inferred from our own experience, whereas in the awake behaving animal, it was directly reported by the monkey. We found that the majority of V4 neurons shifted their color-tuning profile with each change in the background illumination: each time the color of the background on the computer screen was changed so as to simulate a change in illumination, cells shifted their color-tuning function in the direction of the chromaticity component that had been increased. A similar shift was also observed in colored match-to-sample psychometric functions of both human and monkey. The shift in monkey psychometric functions was quantitatively equivalent to the shift in the responses of the corresponding population of cells. We conclude that neurons in area V4 exhibit the property of color constancy and that their response properties are thus able to reflect color perception.
当在不同光源下观察物体时，尽管从物体反射的光的波长组成发生了显著变化，但其颜色不变或变化很小。在先前的研究中，我们通过记录麻醉猴子的V1、V2和V4区域的细胞，探讨了这种颜色恒常性的生理机制。真正的颜色编码细胞，即那些对给定颜色的色块做出反应而不管从其反射的光的波长组成如何的细胞，仅在V4区域被发现。在本研究中，我们采用了不同的方法来测试麻醉和清醒行为猴子中V4细胞的反应。将不同颜色的刺激物嵌入蒙德里安式的多色背景中，用于识别神经元的颜色选择性。然后改变背景的光照，并针对每种背景光照再次测试V4神经元的调谐。对于麻醉的猴子，通过我们自己的经验推断改变背景光照的心理物理学效应，而对于清醒行为的动物，则由猴子直接报告。我们发现，随着背景光照的每次变化，大多数V4神经元都会改变其颜色调谐曲线：每次改变计算机屏幕上背景的颜色以模拟光照变化时，细胞都会朝着色度分量增加的方向改变其颜色调谐功能。在人类和猴子的颜色匹配样本心理测量函数中也观察到了类似的变化。猴子心理测量函数的变化在数量上等同于相应细胞群体反应的变化。我们得出结论，V4区域的神经元表现出颜色恒常性，因此它们的反应特性能够反映颜色感知。
