Lutze Margaret, Pokorny Joel, Smith Vivianne C
Department of Ophthalmology and Visual Science, The University of Chicago, Chicago, Illinois 60637, USA.
Vis Neurosci. 2006 May-Aug;23(3-4):611-6. doi: 10.1017/S0952523806233078.
The PC pathway conveys both chromatic and achromatic information, with PC neurons being more responsive to chromatic (L-M) than to achromatic (L+M) stimuli. In considering the evolution of color vision, it has been suggested that the dynamic range of chromatic PC-pathway processing is tuned to the chromatic content of the natural environment. Anomalous trichromats, with reduced separation of their L- and M-cone spectral sensitivities, have diminished chromatic input to PC-pathway cells. Dichromats, with absent L or M cones, should have no chromatic input to PC-pathway cells. Therefore, the PC-pathway dynamic range of color defectives should be released from any constraint imposed by the chromatic environment. Here we ask whether this results in compensatory enhancement of achromatic PC-pathway processing in color defectives. This study employed a psychophysical method designed to isolate PC-pathway processing using achromatic stimuli. In a pulsed-pedestal condition, a four-square stimulus array appeared within a uniform surround. During a trial, one of the test squares differed from the other three, and the observer's task was to choose the square that was different. A four-alternative, forced-choice method was used to determine thresholds as a function of the contrast of the four-square array to the surround. Seven color defective and four normal observers participated. Results showed no systematic differences between normals and color defectives. There was no enhancement of achromatic processing as compensation for reduced chromatic processing in the PC-pathway system in color defectives. From physiological recordings, PC-pathway achromatic contrast gains of dichromatic and trichromatic New World primates and trichromatic Old World macaques have also been shown to be similar to each other. Our study and the animal studies imply that PC-pathway contrast gain parameters were regulated by factors other than the environmental chromaticity gamut, and may have arisen in a nontrichromatic common ancestor to both Old and New World primates.
PC通路传递颜色和非颜色信息，PC神经元对颜色（L-M）刺激的反应比对非颜色（L+M）刺激的反应更强烈。在考虑色觉的进化时，有人提出颜色PC通路处理的动态范围是根据自然环境的颜色内容进行调整的。异常三色视者的L和M视锥细胞光谱敏感性分离减少，其向PC通路细胞的颜色输入减少。二色视者没有L或M视锥细胞，应该不会向PC通路细胞输入颜色信息。因此，色觉缺陷者的PC通路颜色动态范围应该不受颜色环境施加的任何限制。在这里，我们要问这是否会导致色觉缺陷者非颜色PC通路处理的代偿性增强。本研究采用了一种心理物理学方法，旨在使用非颜色刺激来分离PC通路处理。在脉冲-基座条件下，一个四方刺激阵列出现在均匀的背景中。在一次试验中，其中一个测试方块与其他三个不同，观察者的任务是选择不同的方块。采用四选一的强制选择方法来确定阈值，该阈值是四方阵列与背景对比度的函数。七名色觉缺陷者和四名正常观察者参与了实验。结果显示正常人和色觉缺陷者之间没有系统性差异。在色觉缺陷者的PC通路系统中，没有因颜色处理减少而出现非颜色处理增强的代偿现象。从生理记录来看，新世界二色视和三色视灵长类动物以及旧世界三色视猕猴的PC通路非颜色对比度增益也已被证明彼此相似。我们的研究和动物研究表明，PC通路对比度增益参数受环境色度色域以外的因素调节，可能出现在新旧世界灵长类动物的非三色视共同祖先中。
