[3 parallel channels transmit visual information from the retina. Anatomic and physiologic arguments]

Two hypotheses applied to the information processing of visual messages from the primate retina toward cortical areas are tested against experimental data. The hierarchical theory is weakened by the existence of independent anatomical and physiological parallel channels from ganglion cells to the visual cortex, devoted to specific parameters of the message. X linear and Y nonlinear cells are classified according to the presence or absence of a linear summation process integrating the elementary responses from the subfields which constitute the receptive field. Other response properties might be more loosely correlated with response linearity: X cell responses are sustained, have a long latency and are sensitive to color contrasts. All cells in parvocellular layers of the Lateral Geniculate Body are X, and more than half the magnocellular layers as well. Y cells have brief, transient and short latency responses, very sensitive to monochromatic contrast and are exclusively found in magnocellular layers. Visual information is processed toward the cortex through anatomically and physiologically defined channels specialized in the transmission of different parameters of the visual stimulation.