Reorganization and diversification of signals in vision

Extensive processing and reorganization of information are required as retinally generated signals flow centrally. Insight into some principles of the reorganization and transformations that occur in the early stages of the visual pathway, prior to the higher stages of pattern recognition, is provided through an analysis of receptive fields and cell counts. The rate of information flow is reduced approximately 100-fold by a retinal position-dependent (inhomogeneous) spatial sampling scheme. This principle of specialization, or nonuniform processing, is further elaborated in the retino-cortical mapping. In the central fovea, where the retinal spatial sampling rate is the highest and processing function is uniform, there are about 4000 striate cortical neurons receiving information from each cone. This number, which provides a measure of function multiplicity, drops to about 200 over the range of the near periphery. In the peripheral field beyond eight degrees, where information is compressed at the retina, the functional multiplicity stays approximately constant at 200. As it seems that no two cells perform exactly the same operation, it is concluded that the striate cortex performs many simultaneous functional mappings.