The dependence of the rotation angle on the statistics of stimulus.

We have performed three sets of experiments with different light statistics and estimated the average rotation angle , of the CR-LN model, over the population. The experimental conditions were: A. Light intensities were drawn from a Gaussian distribution (Radiometric units); this is the data set we have used in the main text. B. Light intensities were drawn from a Gaussian distribution with the same marginals for each channel as in A, but with correlation of 0.84 between the red and blue channels. This was done in order to simulate conditions similar to the ones found in natural scenes, where strong correlations between the different colour channels were observed (main text). C. The light intensities were calibrated according to the photoreceptors absorption spectra and kept the same overall contrast in photometric units. Then photometrically calibrated light spectra were drawn from Gaussian distribution as in A. The confidence intervals were calculated using Wilcoxon's test in SPSS. N, SD and SE stand for number of analyzed ganglion cells, standard deviation and standard error respectively.