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

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This research project concerns an apparent contradiction in human color perception. When a human observer is asked to detect a colored target that is barely visible (near threshold), her/his visual system adds color signals across space to achieve maximum sensitivity. But when one views a scene that contains highly colored objects at normal levels of visibility (suprathreshold), the visual system seems to subtract color signals. In this project, we will investigate how those two mechanisms (addition and subtraction) combine in the human visual cortex to produce perception. The project has important implications for all perceptual research. Our results indicate that perception at threshold can be very different from suprathreshold perception. The project's results will explain how these differences relate to color perception. These results will have potential applications across a wide range of areas including communication and industrial design.In our experiments, we will measure the spatial pattern dependence of color perception in humans over a range of cone contrasts from color threshold to highly saturated color, using the technique of hue and saturation scaling. In parallel, we will make measurements of the dependence on spatial stimulus variables of the human cVEP (color-Visual Evoked Potential, an EEG measure of color responses in early visual cortex) recorded with a dense array of electrodes on the scalp. The cVEP experiments have already proven that there are two cortical mechanisms that are the basis of color perception near threshold and suprathreshold: single-opponent and double-opponent neuron populations. The experiments in the continuation project are aimed at studying interactions between the two mechanisms and how interactions affect perceived color.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.