Comparative neurobiology of color vision in humans and animals.

Discrimination of colors was studied using an instrumental learning paradigm in monkeys (Macaque rhesus) and fishes (Carpio cyprinus L.). The confusion matrices composed of probabilities of instrumental responses were treated by factor analysis. The spherical structure of perceptual color space revealed in both animals was similar to that in humans. The four eigenvectors constituting the four-dimensional Euclidean hypersphere correspond to "red-green," "blue-yellow," "brightness," and "darkness" neuronal channels.