Reflection of spreading induction in the human retina.

It was found by Motokawa1) that the indirect induction caused by a colored light at any retinal area disappears when a remote region of the retina is illuminated by another colored light complementary to the former. This phenomenon was attributed by Motokawa to a kind of intereaction between the indirect induction caused by the first colored light and a cer tain propagated process called " spreading induction " initiated by the second colored light. The intereaction is called " neutralization ", be cause this phenomenon occurs only when two colored stimuli are com plementary to each other. It was further shown that the propagation of spreading induction is blocked when there is a retinal image or an after-image of a white bar on the way of propagation. Motokawa et al.2 measured the propagation velocity of spreading induction in human and animal retinae, utilizing the phenomena of neutralization and blocking mentioned above. Kata yama and Aizawa3) used a quite different method of approach for measuring the velocity of spreading induction in the human retina, and obtained re sults consistent with those obtained by the previous authors. The question was raised as to the mechanism of the blocking action of a white light upon the spreading induction. In the present investiga tion it has been elucidated that the blocking action is due to reflection of spreading induction at the after-image of a white bar; as a mirror is to light, so the after-image of a white bar is to spreading induction. This relation will be demonstrated by various examples in the following.