Spectral Sensitivity of the Retinal Receptors

Abstract

RECENT measurements by Granit¹ on the electrical response of individual receptors in the retinæ, of various animals—frog, rat, cat, snake, etc.—have shown that the spectral sensitivity of the cones may vary from red-sensitive receptors with their maximum response at a wave-length of 0.60µ to blue-sensitive elements with their maximum at 0.45 µ. Granit has found four main groups of cones, the largest group (dominators) having a maximum sensitivity at about 0.560 µ, and the three smaller groups (modulators) with maxima in the ranges 0.58–0.60 µ, 0.52–0.54 µ. and 0.45–0.47 µ. Without considering the pros and cons of Granit's dominator-modulator theory, the question arises why, if the cones in the human retina have similar properties, some evidence of their individual sensitivity curves is not obtained from measurements of the luminosity curve by human observers.