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Insub Kim, Sang Wook Hong, Steven Shevell, Won Mok Shim; Reconstructing subjective color experiences across the human visual hierarchy. Journal of Vision 2018;18(10):890. doi: https://doi.org/10.1167/18.10.890.
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The colors we experience are mental percepts. Light of a certain wavelength enters the eye, resulting in a neural representation of the retinal stimulus, but the hues we see depend on higher-level neural signals that cause our visual percepts. Whether the neural representation of chromatic information at each stage of the human visual hierarchy reflects the light stimulus or hue percept remains unclear. To isolate the neural correlates of subjectively experienced colors, neural responses to perceptual color representations were measured with fMRI using chromatic interocular switch rivalry (Christiansen, D'Antona & Shevell, JOV, 2017). In the experiment, two equiluminant, binocularly rivalrous chromaticities were presented to the eyes, swapping between them at a rate of 4.25 Hz. This resulted in slow perceptual alternation between two colors, with each color typically persisting for one second or longer. The chromatic stimulation in each eye was identical over a trial lasting one minute, except that the chromaticities in the two eyes were out of phase and therefore rivalrous. Also, the retinal stimulation was identical regardless of which color was perceived. We constructed an inverted encoding model for color (Brouwer & Heeger, J Neurosci, 2009) from independent training runs in which subjects viewed eight different colors without rivalry. Then, population-level color-selective responses corresponding to each perceived hue during rivalry were reconstructed in the lateral geniculate nucleus (LGN), primary visual cortex (V1), and extrastriate areas (V2, V3, V3A, V4v, and VO1). The reconstructed color responses became progressively more selective for the perceived hue across the visual system. Specifically, subjects' moment-to-moment color experiences corresponded to reconstructed color representations in V3A, V4v, and VO1. This suggests that neural representations of subjective color experience evolve across the human visual hierarchy and may emerge at later stages of cortical visual processing.
Meeting abstract presented at VSS 2018
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