[The perceptual space of brightness in the monkey (the rhesus macaque)]

Brightness discrimination of black-white stimuli (1-37 Cd/m; CIE-31 chromatic coordinate X = 0.340, Y = 0.304) were studied using choice conditioning paradigm in two monkey (Macaque Rhesus). Confusion matrices were composed of probabilities of instrument responses to conditioned and differential stimuli in ten series in which one of the ten intensities was employed as a conditioned one. Confusion matrices were transformed into the correlation matrices between the vectors corresponding to the stimuli. Factor analysis of correlation matrices revealed two-dimensional circular structure of monkey's brightness perceptual space. This space was principally similar with that in humans, fishes, and rabbits. Two eigenvectors which constituted two-dimensional Euclidean space of brightness can be interpreted as bright and dark neuronal channels.