Peng Xinmiao, Van Essen David C
Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA.
J Neurophysiol. 2005 Mar;93(3):1620-32. doi: 10.1152/jn.00793.2004. Epub 2004 Nov 3.
It is widely presumed that throughout the primate visual pathway neurons encode the relative luminance of objects (at a given light adaptation level) using two classes of monotonic function, one positively and the other negatively sloped. Based on computational considerations, we hypothesized that early visual cortex also contains neurons preferring intermediate relative luminance values. We tested this hypothesis by recording from single neurons in areas V1 and V2 of alert, fixating macaque monkeys during presentation of a large, spatially uniform patch oscillating slowly in luminance and surrounded by a static texture background. A substantial subset of neurons responsive to such low spatial frequency luminance stimuli in both areas exhibited prominent and statistically reliable response peaks to intermediate rather than minimal or maximal luminance values. When presented with static patches of different luminance but of the same spatial configuration, most neurons tested retained a preference for intermediate relative luminance. Control experiments using luminance modulation at multiple low temporal frequencies or reduced amplitude indicate that in the slow luminance-oscillating paradigm, responses were more strongly modulated by the luminance level than the rate of luminance change. These results strongly support our hypothesis and reveal a striking cortical transformation of luminance-related information that may contribute to the perception of surface brightness and lightness. In addition, we tested many luminance-sensitive neurons with large chromatic patches oscillating slowly in luminance. Many cells, including the gray-preferring neurons, exhibited strong color preferences, suggesting a role of luminance-sensitive cells in encoding information in three-dimensional color space.
人们普遍认为，在整个灵长类动物视觉通路中，神经元（在给定的光适应水平下）使用两类单调函数对物体的相对亮度进行编码，一类函数斜率为正，另一类斜率为负。基于计算方面的考虑，我们假设早期视觉皮层中也存在偏好中等相对亮度值的神经元。我们通过在清醒、注视的猕猴的V1和V2区域记录单个神经元的活动来检验这一假设，实验中呈现一个大的、空间均匀的斑块，其亮度缓慢振荡，并被静态纹理背景包围。在这两个区域中，对这种低空间频率亮度刺激有反应的相当一部分神经元，对中等亮度值而非最小或最大亮度值表现出显著且具有统计学可靠性的反应峰值。当呈现具有相同空间配置但不同亮度的静态斑块时，大多数测试神经元仍偏好中等相对亮度。使用多个低时间频率的亮度调制或降低幅度的对照实验表明，在缓慢亮度振荡范式中，亮度水平对反应的调制比对亮度变化速率的调制更强。这些结果有力地支持了我们的假设，并揭示了与亮度相关信息的显著皮层转换，这可能有助于表面亮度和明度的感知。此外，我们用亮度缓慢振荡的大色斑块测试了许多亮度敏感神经元。许多细胞，包括偏好灰色的神经元，都表现出强烈的颜色偏好，这表明亮度敏感细胞在三维颜色空间中编码信息方面发挥了作用。
