The mechanism of neutralization of retinal induction was investigated by Motokawa's method of electrostimulation of the eye. By neutralization it is meant that an after-effect of a colored stimulus is extinguished by a second stimulus complementary to the former.
1. When two complementary stimluli are separated by a sufficiently great lateral distance, neutralization occurs at all values of the interval between both stimuli.
2. When the separation of both stimuli is small, no neutralization occurs for time intervals shorter than a certain limit. For example, the critical interval was found to be 500 msec. for a separation of 3mm. on a plane at 30cm. from the eye.
3. The mechanism of this phenomenon was investigated, and it was elucidated that for a certain period after establishment of retinal induction the latter remains “inert” and suffers from no neutralization. This period was designated an “inert period”.
4. Within the “inert period” the second stimulus is ineffective to neutralize the prestablished induction, but has the power to establish its own induction. Therefore the “inert period” cannot be a kind of refractoriness. In the “inert period” both kinds of induction can coexist without neutralizing one another.
5. The absence of “inert period” for a greater separation of both stimuli is only apparent, because the “inert period” is over before the neutralizing effect (spreading induction) caused by the second stimulus reaches the point at which neutralization is tested.