Mechanisms of Color Perception: Dependences on Color Contrast and Spatial Pattern

对大多数人来说，色彩感知是视觉体验的一个主要方面。本研究项目旨在解决人类色彩感知中的一个明显矛盾。当一个人类观察者被要求检测一个几乎不可见的彩色目标时，视觉系统将跨空间的颜色信号相加，以达到对弱刺激的最大灵敏度。然而，当一个人看到一个高度彩色的场景时，视觉系统会在不同的位置接收不同的颜色信号，从而导致高度依赖于颜色对比的颜色外观。加减法之间的明显矛盾可以通过假设来解决，即当颜色刺激几乎不可见时，颜色感知在阈值处增加颜色信号，但当颜色刺激远高于阈值时，颜色感知会减去颜色信号。这项研究通过研究颜色感知如何依赖于空间中颜色的模式来验证这一假设。如果视觉系统增加或减少颜色信号，间距对颜色感知的影响是不同的。更好地理解视觉系统如何处理颜色可能会在照明设计或彩色图形等领域带来进步。该项目包括培训年轻科学家通过测量行为和大脑活动来研究人类视觉的方法，以及向公立学校的学生进行科学宣传。实验将测量人类超阈值颜色感知的空间模式依赖性，并将超阈值结果与颜色阈值结果进行比较。使用了两种不同的技术来研究超阈值颜色感知：色调和饱和度缩放以及反应时间。该项目还包括测量人类cVEP（颜色-视觉诱发电位，早期视觉皮层颜色反应的脑电图测量）及其对不同颜色对比度水平的空间刺激变量的依赖。cVEP实验的目的是确定阈值附近和超阈值颜色感知基础的皮层机制。计算模型将用于拟合心理物理学和cVEP数据。

Color perception is a primary aspect of visual experience for most people. This research project aims to resolve an apparent contradiction in human color perception. When a human observer is asked to detect a colored target that is barely visible, the visual system sums color signals across space to achieve maximum sensitivity to the weak stimulus. However, when one views a highly-colored scene, the visual system takes the difference between color signals at different locations, leading to color appearance that is highly dependent on contrasts in color. The apparent contradiction between adding and subtracting can be resolved by the hypothesis that color perception adds color signals at threshold, when they are barely visible, but subtracts color signals when color stimuli are well above threshold. This research tests this hypothesis by studying how color perception depends on the pattern of the color in space. Spacing has different effects on color perception if the visual system is adding or subtracting color signals. Better understanding of how the visual system processes color may translate to advances in fields such as lighting design or color graphics. The project involves training of young scientists in methods of studying human vision through measuring behavior and brain activity, as well as science outreach to public school students.The experiments will measure the spatial pattern dependence of suprathreshold color perception in humans and compare suprathreshold results with those at color threshold. Two different techniques for studying suprathreshold color perception are used: hue and saturation scaling, and reaction times. The project also includes measurements of the human cVEP (color-Visual Evoked Potential, an EEG measure of color responses in early visual cortex) and its dependence on spatial stimulus variables at different levels of color contrast. The aim of the cVEP experiments is to determine the cortical mechanisms that are the basis of color perception near threshold and suprathreshold. A computational model will be used to fit the psychophysics and cVEP data.