Probability summation model for heterochromatic luminance additivity failure at absolute visual threshold

Vos and Wabraven recently derived a new set of foveal primaries. These primaries, in conjunction with the revised zone fluctuation theory of color vision, account for more psychophysical color vision data than any other model to date. The new primaries depend heavily on Abney's law, and their success has been challenged by Guth's observations of additivity failure at absolute threshold. The present paper develops a probability summation model which accounts for threshold additivity failure within the framework of Vos's and Walraven's assumptions.