Fig. 10. Potential functions of chromatically nonlinear cells.

a Schematic depiction of linear and nonlinear models of chromatic integration. b Examples of green (left) and UV (right) channels in natural images. The red circle shows the receptive field size used in both models. c Heatmap of response differences from the two models (nonlinear model minus linear model) for 10,000 randomly selected patches of the images in b. Gray points show locations where the modeled receptive field was partly outside the image range. d Contrast values for the UV and green channels along the three columns marked by the dashed lines in b. Arrows point towards regions of opposite contrast in the two color channels. e Comparison of the two model responses for low to moderate activation. The inset shows the same measurement over the entire activation range. f Comparison of midpoints for fitted sigmoids to the contrast values of the green and UV channels along with all columns in the images of b.