Fig. S2.

Image statistics of (A) pixelwise luminance, (B) contrast, (C) histogram skew of the four conditions. Luminance was calculated by averaging the mean luminance of all pixels in each image then averaging across images. Contrast was calculated with pixelwise luminance's standard deviation divided by its mean for each image, averaged across images. Skew was calculated as the third standardised momentum of the luminance histogram of each image, averaged across images (Motoyoshi et al., 2007). (D) Difference in power spectra across the 15 images (3 objects × 5 levels) calculated for each image pair and then averaged across images.