IV

TRIPLE CONDUCTING PATHWAY IN THE VISUAL SYSTEM AND TRICHROMATIC VISION

by Hsiang-Tung Chang

Yale University School of Medicine, New Haven, Connecticut.

In 1930 Professor Piéron made a very significant observation on the minimum time required for the recognition of different colors. He found that the recognition time for red was the shortest, that for green the next and that for blue the longest. From the physiological point of view, the difference in time for the appreciation of the three fundamental colors would imply a difference in speed of conduction of nerve impulses carrying these chromatic qualities. During a study of action potentials of the visual cortex we have found evidences supporting the theory of trichromatic conduction as suggested by the remarkable observations by Professor Piéron more than twenty years ago. As a tribute to one of the great scientists of our time I would like to make, on this occasion, a brief summary of our study which has been inspired by his prescient revelation.

As we have demonstrated previously the primary response of the visual cortex of the cat to the stimulation of optic nerve with a single electric shock consists of a small initial deflection, three successive surface positive spike-like deflections and a broad wave sometimes followed by another prolonged negative wave as shown in Figure 1. An analysis of this compound potential revealed that the pattern of the response is made up of several algebraically summated components as shown in Figure 2 in which A is a small deflection produced by the electric field