Spectral tuning of dichromats to natural scenes

Multispectral images of natural scenes were collected from both forests and coral reefs. We varied the wavelength position of receptors in hypothetica l dichromatic visual systems and, for each receptor pair estimated the perc entage of discriminable points in natural scenes. The optimal spectral tuni ng predicted by this model results in photoreceptor pairs very like those o f forest dwelling, dichromatic mammals and of coral reef fishes. Variations of the natural illuminants in forests have little or no effect on optimal spectral tuning, but variations of depth in coral reefs have moderate effec ts on the spectral placement of S and L cones. The ratio of S and L cones t ypically found in dichromatic mammals reduces the discriminability of fores t scenes; in contrast, the typical ratio of S and L cones in coral reef fis hes achieves nearly the optimal discrimination in coral reef scenes. (C) 20 00 Elsevier Science Ltd. All rights reserved.