Two Kinds of Scotopic Mechanisms in the Human Retina

Retinal processes were studied by the method of electrostimulation at 20° and 50° from the fovea.1. At the light-threshold there appear three processes of different time courses. The slowest one represents the excitation of rods. The other two processes correspond to the yellow and the blue process respectively, judging from their crest times. Therefore, they are denoted by Y and B.2. At the light-threshold and in the photochromatic interval, the two processes, Y and B appearing always hand in hand, are equal to each other in magnitude and remain constant irrespective of the wave-lengths of illuminating lights. Therefore, they are called “ a twin-process.” This process subserves scotopic colorless sensations in conjunction with the rod-process.3. At the color-threshold, either Y or B component of the twin-process is depressed according to whether the wave-length of illuminating light is shorter or longer than 505mμ, but the other component remains intact. This finding corresponds to the psychological fact that at the color-threshold spectral lights give rise to yellow or blue sensation.4. The twin-process is a scotopic process having some properties similar to those of photopic processes. It differs from the rod-process in the following points; i) it originates in ofd elements or on/off-elements, ii) it exists only below the color-threshold, iii) its spatial distribution corresponds to the density distribution of cones, iv) its time constantsare much shorter than that of the rod-process. 5. The important role played by inhibition in the formation of color sensations is discussed.