Heterochromatic additivity and the CFF response

The validity of the heterochromatic additivity principle (Abney's Law) was examined using bichromatic combinations of test wavelengths adjusted to equal luminance by a CFF technique. Additivity failures qualitatively similar but smaller than those resulting from foveal threshold, incremental threshold, or direct brightness matching techniques were evident for a number of bichromatic combinations. These results suggest that the CFF response is influenced, to a small degree, by the activity of opponent-color channels.