E. N. Sokolov
Lomonosov Moscow State University
Factor analysis of a matrix of probabilities of instrumental conditioned reflexes to color stimuli in rhesus monkeys revealed four principle components that correspond to red-green, blue- yellow, brightness and darkness vectors. The lengths of the four orthogonal vectors representing colors are of a constant magnitude. This suggests that color stimuli are located on a hypersphere in four-dimensional space. Three polar coordinates (angles) of the hypersphere correspond to hue, lightness and saturation similar to those found in humans. Local patches of the hypersphere that correspond to response areas of color selective neurons in V4 of the monkey are suggestive of a color map as a mechanism of colortopic projection analogous to retinotopic, tonotopic and somatotopic projection maps. Under reinforcement, as in the process of associative learning, the color selector map induces modifications in plastic synapses of command neurons such that synaptic weight vectors become collinear with an input excitation vector generated by the conditional stimulus on the color map.
The coding of information in neuronal nets is closely related to the process of mapping. The cortical maps of receptive surfaces revealed in somatotopic and retinotopic projections serve as examples. In so far as different sound frequencies are systematically positioned along the Organ of Corti, the tonotopic cortical projection can be regarded as a subtype of the somatotopic one. The shift of a stimulus along the receptive surface results in a corresponding dislocation of the excitation maximum with respect to the cortical map. A problem arises concerning neuronal representations of stimuli that, being modified, are not shifted along a receptive surface, such as color change by local stimulation of the retina. The main hypothesis under consideration in this paper states that local stationary stimuli are also represented topically on maps composed from feature-selective neurons. The realization of such a representation is achieved by the generation, at the receptor level, of a____________________
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Publication information: Book title: Origins:Brain and Self Organization. Contributors: Karl Pribram - Editor. Publisher: Lawrence Erlbaum Associates. Place of publication: Hillsdale, NJ. Publication year: 1994. Page number: 463.
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