A new interaction of light and electricity in stimulating the human retina

Purkinje (1825, p. 34) observed that an electric current sent through the eye could affect the subjective brightness of a light seen at the same time. From his observations and those of later writers, especially Helmholtz (1896, p. 247) and Bogoslowski & Segal (1947), it has become clear that currant flowing from vitreous to sclera causes a brief apparent brightening when it is switched on and a brief apparent dimming when it is switched off. Current flowing from sclera to vitreous has the opposite effects. Extrapolating from these observations, one might well guess that if two lights of different colour were cast on the retina in regular alternation, and if alternating current at the same frequency were passed through the eye at the same time, the colour seen should vary with the phase-relation between the light and the electricity, being for some phase-relations more like one of the two lights alternated, and for other phase-relations more like the other. In the experiments described here, this guess is tested and found to be correct.