Ramith Ambati^1,2 (), William Narhi-Martinez^3,4, Angela Brown^1,2, Julie Golomb³, Delwin Lindsey^2,3; ¹The Ohio State University College of Optometry, ²Graduate Program in Vision Science, The Ohio State University, ³Department of Psychology, The Ohio State University, ⁴Department of Psychology, Yale University

Humans can perceive a rich set of colors, but the neural mechanisms underlying color appearance are not fully understood. One influential theory, Hering’s “color-opponent” theory, asserts that hue appearance is governed by neural responses signaling elemental redness, greenness, blueness, and yellowness sensations, which are organized into two color-opponent processes: redness-greenness and blueness-yellowness. Despite abundant behavioral evidence consistent with Hering’s theory, no one has found corresponding hard-wired neural processes in cerebral cortex. Inspired by these conflicting findings, we used multi-voxel pattern analysis and Representational Similarity Analysis (RSA) to investigate the neural representation of hue in human cortex. Ten participants performed a series of Hering-style hue-scaling tasks in the fMRI scanner. On each trial, they viewed a rotating spiral colored with one of 8 hues: their predetermined personal unique red, yellow, green, and blue hues, and their binary-composite hues: orange, lime, cyan, and purple. During each block of trials, participants performed one of four hue-scaling tasks (redness, yellowness, greenness, or blueness), where they rated with 4-alternative button press (“none”, “some”, “mostly”, “all”) the amount of the corresponding elemental sensation present in each colored spiral. Our analyses included whole-brain searchlight analysis using RSA to compare neural similarity patterns from cortical responses to hypothetical similarity patterns based on the hue-scaling task and/or spiral hue. These analyses revealed color-selective cortical areas in and around hV4, where color information was represented according to hue similarity, regardless of task. By comparison, dorsal regions of frontal (FEF) and parietal (IPS) cortex, which were non-color-selective under passive viewing, showed Hering-like representational patterns of hue-scaling that were shaped by both hue and task. Our results have interesting implications for Hering’s theory, and hue appearance more broadly, and also demonstrate the power of individualized hue stimuli and RSA analyses to dissociate task-dependent from task-invariant representations of hue in the brain.