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Sang Wook Hong, Qing Yu, Won Mok Shim; Color representation in lateral geniculate nucleus: a human fMRI study. Journal of Vision 2015;15(12):21. doi: 10.1167/15.12.21.
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Studies in non-human primate visual system show a distinction between two cardinal chromatic channels, parvocelluar (L-M) and koniocellular (S-(L+M)), in neuronal responses of the lateral geniculate nucleus (LGN). Thus, it is believed that colors which vary on both cardinal channels cannot be represented in LGN but can only be encoded at the cortical level where a major transformation of chromatic signals occurs, known as the higher-order color mechanism (Krauskopf et al., 1986). However, color representations in human LGN are largely unknown. In the current study, we investigated color representations in LGN and the primary visual cortex (V1) in human visual system using functional Magnetic Resonance Imaging (fMRI) and a forward encoding model (Brouwer & Heeger, 2009). In each experimental run, observers viewed equi-luminant concentric ring patterns, composed of one of eight colors (four colors varying on only one channel, four colors varying on both channels) and equal-energy-spectrum white, which alternated drifting in expanding and contracting directions. In V1, we found clear population-level color tuning responses which peaked at each of the viewed colors, indicating that colors of both chromatic channels and combinations of them are encoded in V1. In contrast, in LGN, distinct tuning responses were found for colors varying along the koniocellular channel, whereas tuning responses for colors varying along the parvocellular channel were indistinguishable. These large-scale population-level color tuning responses may indicate the lack of an S-OFF mechanism in LGN. In sum, our results provide evidence for a major transformation of color representation from LGN to V1 in human visual system, consistent with findings in non-human primates.
Meeting abstract presented at VSS 2015
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