ABSTRACT
Direct estimation of subjective differences between colours is the traditional method of investigation of colour vision in humans. Multidimensional scaling of subjective suprathreshold differences between perceived colours obtained by direct estimations reveals a spherical structure of perceptual colour space in normal subjects. Sokolov and Izmailov (1984) showed that different colour stimuli varying in hue and brightness were located on a spherical surface in a four-dimensional Euclidean space. The distances between points representing colours correlated closely with subjective differences. In the spherical model of colour discrimination, four Cartesian co-ordinates of each colourpoint represent excitations of neuronal channels for red-green, yellow-blue, brightness and darkness. Three spherical co-ordinates of the hypersphere correspond to subjective aspects of colours: hue, brightness and saturation (Sokolov and Izmailov, 1984).
