A General Spherical Model of the Discrimination of Color Signals

The problem of the metric relations between perceived suprathreshold differences in brightness and color is well known in the science of colors [1,2]. The basic difficulties in dealing with this problem arise in connection with the impossibility of making direct measurements of differences among stimuli that vary simultaneously both in intensity and in spectral composition. When such measurements are made, subjects involuntarily assess either only chromatic or only achromatic differences, depending on what type of difference is more marked in the stimulation.