Abstract
The human retina was stimulated by a subthreshold electric shock, and the change in electrical excitability caused by this stimulus was investigated by another electrical stimulus delivered at varying intervals after cessation of the sensitizing stimulus. Stimulating electrodes were placed at the forehead and the occiput, the index of excitation being an electric phosphene.
1. The excitability-time curve shows a periodic course, the amplitude of oscillation decreasing exponentially.
2. The frequency of oscillation is 18 cycles per sec., and this agrees closely with the lowest optimum frequency of the retina as determined by stimulation with alternating currents.
3. More detailed study of this phenomenon revealed that some oscillations with higher frequencies are superimposed upon the fnndamental oscillation observed above. This finding corresponds to the fact that there appear three or more minima in the strength-frequency curve obtained in stimulation experiments with alternating currents.
4. Thus, the periodic excitability of the human retina can be demonstrated in the two ways, i. e. by the present method and by the method of resonance.
