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Kathy Mullen, Serge Dumoulin, Robert Hess; Color processing in the human LGN and cortex measured with fMRI. Journal of Vision 2007;7(15):4. doi: 10.1167/7.15.4.
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I will report on our results measuring the fMRI BOLD responses of the different cortical areas and the LGN to chromatic and achromatic stimuli. We used an fMRI (4T) experimental protocol that controls for attention and allows us to compare responses to L/M opponent (RG), S-cone (BY) and achromatic contrast within the same scan, using sinewave ring stimuli (0.5cpd). Our results cover three main areas. 1. In the cortex we support previous results that BOLD responses in V1 and VO are biased to color, whereas areas MT and V3a show a dominant achromatic response (e.g. Mullen, K.T. et al., European Journal of Neuroscience, 25, 491–502, 2007). 2. We find that the LGN responds best to red-green stimuli at 2 & 8 Hz, whereas blue-yellow responses are much more weakly driven at both temporal rates. This suggests that the color response of P-cells, which are red-green sensitive, dominates the fMRI response in human LGN, at least for the conditions used here. 3. When we compare the responses of the LGN and V1 we observe that a key change from the LGN to V1 is a significant relative boost in the blue-yellow response, occurring at the low temporal rate (2Hz). This robust cortical BY response is evident in all color responsive cortical areas.
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