Suppression of color contrast and retinal induction by mechanical pressure applied to the eyeball.

Color and brightness contrasts are familiar visual phenomena, but their mechanisms have long remained obscure. Motokawa1)-4) found a phenomenon which is very likely to represent a retinal process underlying contrast and other similar visual phenomena, and termed it retinal in duction. This phenomenon can be found not only in the human eye, but also in mammalian retinas.5) Further it was shown that retinal in duction was caused not only by colored light, but also by intermittent white lights) and by alternating currents.7) Two kinds of retinal induction were distinguished by Motokawa ; the induction effect remaining within a pre-illuminated retinal area after exposure to colored light is called direct induction, and the one set up around the retinal area pre-illuminated is called indirect induction. Direct or indirect induction usually remains unchanged for about 20 seconds, but is extinguished by a second exposure of the retina to a stimulus of complementary color. This phenomenon is called neutralization of retinal induction Motokawa and Ebe8) showed that a pre-established retinal induction could not be abolished by antidromic stimulation of the optic nerve, and Nakagawa and Kohata9) found that a pre-established retinal induction could not be abolished by illumination with white light of very high intensity. In a previous paper10)11) we studied the effect of a mechanical pressure applied to the eyeball upon the excitability of the eye and upon the supernormal electrical excitability caused by colored light. The present in vestigation represents an extension of the preceding one and deals with the effect of mechanical pressure upon retinal induction, and color contrast.