Classification of equiluminant color gratings in the human visual cortex with multi-voxel pattern analysis: A color space-free approach O F Gulban, A I Isik, H Boyaci |
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Dept. of Psychology & Nat. MR Research Center, Bilkent University, Turkey
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| While the early stages of color processing is well understood, how color perception is achieved in the cortex still remains unknown. In order to investigate the spatial organization of color tuned neurons in the cortex, we conducted an fMRI experiment and used Multi Voxel Pattern Analysis (MVPA) technique to analyze the data. Our main purpose was to test whether color information in the cortex can be decoded successfully using MVPA methods. In previous studies that explored this hypothesis (Brouwer & Heeger, 2009) researchers used colors from standard color spaces assuming perceptual equiluminance, and used specific hues instead of color-opponent stimuli. In the present study, we first conducted a psyhophysical experiment in order to obtain isoluminant colors per participant to use in the fMRI experiment. Then, we presented isoluminent red-green and blue-yellow grating patterns in a block design paradigm with a demanding attention task. GLM results and event related averaging showed no difference between the mean BOLD responses for the stimuli across all the runs. Within functional regions of interest that correspond to the visual position of the colored stimuli, successful classification results were observed across participants. We conclude that it is possible to classify color-opponency information in the occipital cortex. |
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