Large-scale color biases in the retinotopic functional architecture are region specific and shared across human brains

Despite the functional specialization in visual cortex, there is growing evidence that the processing of chromatic and spatial visual features is intertwined. While past studies focused on visual field biases in retina and behavior, large-scale dependencies between coding of color and retinotopic space are largely unexplored in the cortex. Using a sample of male and female volunteers, we asked whether spatial color biases are shared across different human observers, and whether they are idiosyncratic for distinct areas. We tested this by predicting the color a person was seeing using a linear classifier that has never been trained on chromatic responses from that same brain, solely by taking into account: (1) the chromatic responses in other individuals’ brains and (2) commonalities between the spatial coding in brains used for training and the test brain. We were able to predict the color (and luminance) of stimuli seen by an observer based on other subjects’ activity patterns in areas V1-V3, hV4 and LO1. In addition, we found that different colors elicited systematic, large-scale retinotopic biases that were idiosyncratic for distinct areas and common across brains. The area-specific spatial color codes and their conservation across individuals suggest functional or evolutionary organization pressures that remain to be elucidated. Significance statement Does a given color elicit comparable neural activity in two different observers? Do colors elicit area-specific response patterns? To address these questions, we predicted what color someone is seeing based on their brain activity, using only knowledge of color responses from other observers' brains. Estimating the commonalities across brains in the way they respond to achromatic, spatial stimulation allowed us to retinotopically align different brain responses to each other in a common response space. In this space derived without any color responses we could decode across individuals what color an observer was seeing and found spatial color biases that differed between areas. Our results demonstrate systematic dependencies between chromatic and visual field representations that are area-specific and preserved across observers.