Fig. 6: The functional organization of DKL hue-direction map and its relationship with COFDs.

a–c COFDs contours (a), DKL hue-direction map (c), and spatial overlay (b). Second and third row panels are zoom-in views of selected regions. Both pinwheel (black arrows) and linear (white arrows) structures exist in DKL hue-direction map. Scale bars: a top 1 mm, a middle and bottom 0.5 mm; applies to a–c. Note that the first image in a is same as Fig. 4h. The cortical region in the first row of a–c is same region shown Fig. 4a–h. d, e Spatial relationship between DKL hue-direction domains and each type of COFD. Rows in d correspond to comparisons of hue maps with L (top), M (middle), and S (bottom) COFDs. DKL hue directions indicated at bottom of e also apply to columns in d and corresponding colors (and gray) are shown at the top of d. The bivariate histograms show systematic relationship between COFDs and DKL hue-direction domains. e The angles defined by the top 10% of pixel densities in each bivariate histogram for each cone type plotted in relation to each hue direction. Y-axis is the angle calculated from each bivariate histogram. f Hue tuning curves calculated from the means of ISI pixel values within each COFD region in response to each DKL hue direction. g Hue tuning curves calculated from the means of ISI pixel values within each COFD-intersection region in response to each DKL hue direction. Method of curve fitting used in f and g is described in Methods. Another case is shown in Supplementary Fig. 4e, f. h Cone-opponent signals mixing model based on COFDs. The spatial organization and overlap of COFDs follows Stage 3 mixing rules for color opponency and color appearance mechanisms, and creates hue tuning. The organization allows four intersections between L/M and S/(L+M) cone-opponent mechanisms at the four overlapping regions of COFDs, to generate color appearance mechanisms and encompasses the four “unique colors” (red—RG; green—GR; yellow—YB; blue—BY).