1988'1, p.137
Izmailova T. V. , Sokolov Ye. N. , Izmailov Tch. A. , Livshits G. Ya.
General spherical model of discrimination between coloured signals

156 colors (25 spectral and one neutral lights varying from 0,2 cd/m2 to 200 cd/m2) were classified according to a five categories (red, yellow, green, blue, white) color-naming technique. Experimental data were analyzed by means of a multidimensional scaling procedure. It turns out that minimal dimensionality of the Euclidian space providing a linear relationship between the interpoint distances and the estimated color differences is four. Color points do not fill completely the four-dimensional space but are located on a hypersphere. The phenomena of constant hue and color opponency of spectral stimuli were used to correlate the coordinates with the neurophysiological data. The first (X1) and the second (X2) cartesian axes correlate with red-green and blue-yellow opponent channels. The third (X3) and the fourth (X4) cartesian axes correlate with bright and dark nonopponent channels. At the same time three spherical coordinates are directly connected with three psychological color characteristics - hue, saturation, and brightness.