role of cultural factors and language in the utilization of color vision. Another line of research led Chingis Izmailov to a spherical model of facial expressions of emotions. The sphere is four-dimensional, with interpoint Euclidean distances nearly proportional to numerical estimates of emotional differences. The axes of the sphere are interpreted as the opponent pleasant-unpleasant and active-passive channels, the remaining two being interpreted as “strength” and “calmness.” Chingis Izmailov hypothesized that spherical models and other metric structures may not be applicable to properties of categorizable perceptual objects. Thus, colors lose their metric arrangement when they are colors of differently categorized objects (such as “apple” and “banana”) rather than colors of objects that do not belong to different categories (e.g., apertures or pigment patches). Chingis Izmailov also hypothesized, based on the evoked potential experiments, that the system responsible for detection of changes in brightness is physiologically different from the system responsible for detecting spatial patterns. In the later period of his life Chingis Izmailov was working on a comprehensive theory of perception as having a formal structure of a language, with levels analogous to those of graphemes/phonemes, letters, and words. The “graphemes/phonemes” are represented by two-dimensional circular spaces (such as for line orientation or shades of gray), which are combined into higher-dimensional spherical stimulus spaces representing “letters” (such as the four-dimensional color space), which in turn are combined into “words,” categorized images of objects. Publications Monographs Измайлов Ч. А. (1980). Сферическая модель цветоразличения. М.: МГУ. [Izmailov Ch. A. (1980). Spherical model of color discrimination. Moscow: Lomonosov Moscow State University Press (in Russian)]. Соколов Е. Н., Измайлов Ч. А. (1984). Цветовое зрение. М.: МГУ,. [Sokolov E. N., Izmailov Ch. A. (1984). Color vision. Moscow: Lomonosov Moscow State University Press (in Russian)]. Измайлов Ч. А., Соколов Е. Н., Черноризов А. М. (1989). Психофизиология цветового зрения. М.: МГУ. [Izmailov Ch. A., Sokolov E. N., Chernorizov A. M. (1989). Psychophysiology of color vision. Moscow: Lomonosov Moscow State University Press (in Russian)]. Articles Izmailov Ch.A., Chernorizov A.M. A Geometrical Approach to Research into Signal Recognition in Visual Systems of Humans and Animals. // Psychology in Russia: State of the Art, Vol. 3, 2010, р. 301–332. Bimler D.L., Paramei G.V., Izmailov Ch.A. Hue and sturation shifts from spatially induced blackness. // J. Opt. Soc. of Am. 2009. 26. 1. 163–172. Izmailov Ch.A., Zimachev M.M. Detection of bimodal stimuli in the frog retina. // Neuroscience and Behavioral Physiology.