 His experimental work and mathematical models were primarily based on various forms of multidimensional scaling, and on amplitudes of evoked potentials in humans and electroretinogram in frogs in response to an abrupt change of one stimulus to another.Izmailov's model of color space represents both aperture and pigment colors as points on a four-dimensional sphere, such that the Euclidean distance (chord length rather than arc length) between two colors is nearly proportional to the estimates of their dissimilarity.Two axes of the sphere correspond to the color-opponent channels (red-green, blue-yellow), the other two axes represent the achromatic “whiteness” and “darkness” channels which Chingis Izmailov distinguished from brightness.