Spatial Summation of Optic Stimuli in the Human Retina as Revealed by Electrical Stimulation

Abstract

Spatial summation in the human retina was studied with increases of electrical excitability by illumination as the indes.
1. The maximum incrase in electrical excitability is reached in 2 seconds after an illumination. This amount was expressed in percentage of the electrical excitability in the dark and denoted by ζ. The value of ζ after an exposure to five circular patches 1° in diameter was always higher than the value for a single patch of the same size. The closer the five patches to one another, the greater the value of ζ.
2. Two semi-circles separated by an unstimulated region of 2° was used to study summation at various parts of the retina. The value of ζ was greater by a constant amount for both semi-circles together than for a single semi-circle irrespective of the location in the retina.
3. ζ-log area curves were sigmoid in shape and their slope was the same in the fovea and in the periphery. These findings suggest that there are little regional differences with regard to summation.
4. Two semi-circular patches in juxtaposition were employed to investigate the interaction between colored lights. Summation was most striking between same colored areas, and fairly marked between red and green fields or green and blue areas, but there was no indication of summation at all between red and blue areas. The result was explained on the basis of Young-Helmholtz's theory of color vision.