COLOR PROCESSING IN HUMAN CORTEX

这个项目的目标是促进对颜色如何在大脑皮层中表现的理解。虽然颜色感知的第一阶段被很好地理解，但对随后的处理却知之甚少。这项提议的总体目标是确定皮层中支持第二阶段处理的神经群，即对手颜色表征。知觉研究表明，这种表征将颜色编码为锥体信号的三种组合，编码红色和绿色、蓝色和黄色以及浅色和深色的相对数量。这些感知机制：1)信号特定的，锥体信号的线性组合；2)即使空间格局发生变化，也能保持其色彩特性；3)各自独立地改变响应性；4)对空间频率和方位具有选择性；5)将信号传递给其他非基数色机制。但是对立颜色机制的神经基础仍然未知。当外侧膝状核的旁细胞神经元接受相反的锥体输入时，这些细胞不能表现出上面列出的特性2和3。V2-V4区域的一些神经元被调整为非基本色，并且对空间频率有选择性，但将这些神经元与感知结果联系起来的关键实验尚未进行。这里提出的工作旨在确定可以解释对手颜色机制的神经种群。人类视觉区域和LGN对多种颜色刺激的反应性将使用功能性磁共振成像进行测量。一系列的实验将测试对手颜色机制的5个关键属性。首先，将测试颜色响应的线性度。接下来，将在几个空间频率和适应性刺激下测量颜色反应，测试属性2、3和5。最后，适应转移的测量将测试性质4。反应显示这些特性的视觉区域可能包含支持颜色感知的神经元群。显示不同属性的群体很可能在不同的视觉区域中被发现，这有助于揭示每个区域在颜色感知计算中的具体作用，并测试颜色感知的计算理论。

The goal of this project is to advance understanding of how color is represented in cortex. While the first stages of color perception are well understood, much less is known about subsequent processing. The general aim of this proposal is to identify neural populations in cortex that support a second stage of processing, the opponent colors representation. Perceptual studies reveal that this representation encodes color as three combinations of cone signals, encoding relative amounts of red and green, blue and yellow, and light and dark. These perceptual mechanisms: 1) signal specific, linear combinations of cone signals; 2) maintain their color properties even as spatial pattern changes; 3) change their responsiveness independently of each other; 4) are selective for spatial frequency and orientation; 5) pass signals to other, non-cardinal color mechanisms. But the neural bases of opponent colors mechanisms remain unkown. While parvocellular neurons in the lateral geniculate nucleus receive opposing cone inputs, these cells fail to show properties 2 and 3, listed above. Some neurons in areas V2-V4 are tuned for non-cardinal colors, and are selective for spatial frequency, but the crucial experiments linking these neurons to perceptual results have not been performed. The work proposed here is designed to identify neural populations that can account for the opponent colors mechanisms. The responsiveness of human visual areas and LGN to stimuli of many colors will be measured using functional magnetic resonance imaging. A series of experiments will test for the 5 key properties of opponent color mechanisms. First, the linearity of color responses will be tested. Next, color responses will be measured at several spatial frequencies and in the presence of adapting stimuli, testing for properties 2, 3, and 5. Finally, measurements of transfer of adaptation will test for property 4. Visual areas whose responses show these properties are likely to contain populations of neurons that support color perception. Populations showing the different properties will most likely be found in different visual areas, helping to reveal the specific role of each area in the computations that underly color perception, and testing computational theories of color perception.