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Dany V. D'Souza, Barry Lee, Jens Frahm; Do chromatic responses in V1 match retinal output or perceptual performance?. Journal of Vision 2007;7(15):60. doi: https://doi.org/10.1167/7.15.60.
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Chromatic responses of cone-opponent retinal ganglion cells are present up to higher temporal and spatial frequencies, and for red-green, to higher visual eccentricities, than in psychophysical measurements. Our goal is to track chromatic signals using fMRI through different cortical areas to ascertain the locus of the perceptual filtering. We describe here responses in VI to chromatic gratings as a function of spatial and temporal frequency and eccentricity. Subjects were imaged with a 2.9 T MR scanner (Siemens Tim Trio). Visual areas and eccentricities were mapped using blackwhite checked meridian and ring stimuli. BOLD fMRI responses were measured to sinewave counter-phase circular gratings (equal cone-contrast), either red-green, blue-yellow or luminance as a function of spatial and temporal frequency. Our results suggest that there is little loss of red-green or blue-yellow responsivity with eccentricity in V1. We observed an interaction with spatial frequency which may account for previous contrary reports (Vanni et al., EJN, 24,1821, 2006). Preliminary results indicate that V1 responds to higher spatial and temporal frequencies with chromatic gratings than is the case perceptually. These results suggest that responses in V1 are directly related to thalamic input; filtering of the chromatic signal must occur in later visual areas.
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