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

颜色感知是大多数人视觉体验的主要方面。该研究项目旨在解决人类颜色感知中的一个明显矛盾。当人类观察者被要求检测一个几乎不可见的有色目标时，视觉系统会将空间中的颜色信号相加，以实现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，视觉系统会在不同位置的颜色信号之间产生差异，导致颜色外观高度依赖于颜色的对比度。加减之间的明显矛盾可以通过假设来解决，即颜色感知在阈值处添加颜色信号，当它们几乎不可见时，但是当颜色刺激远高于阈值时，减去颜色信号。本研究通过研究颜色感知如何依赖于空间中的颜色模式来验证这一假设。如果视觉系统增加或减少颜色信号，间距对颜色感知有不同的影响。更好地理解视觉系统如何处理颜色可能会转化为照明设计或彩色图形等领域的进步。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，以及向公立学校学生进行科学宣传。实验将测量人类阈上色觉的空间模式依赖性，并将阈上结果与色觉阈下的结果进行比较。使用两种不同的技术来研究阈上颜色感知：色调和饱和度缩放，和反应时间。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EEG测量）及其对不同颜色对比度下空间刺激变量的依赖性。cVEP实验的目的是确定作为阈值附近和阈上颜色感知的基础的皮层机制。将使用计算模型来拟合心理物理学和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.