Abstract
The effect of combined stimuli, black and white, upon the electrical excitability of the human retina was investigated under various conditions of light adaptation.
1. The electrical excitability of the resting retina increases in accordance with the degree of light adaptation when the intensity of adapting light is below 25 lux.
2. The effect of a circular bright stimulus to increase electrical excitability is enhanced when the patch is enclosed by a black ring (simultane-ous induction).
3. Dissipation of induction is facilitated by adapting light.
4. There is an optimum adaptation state for brightness induction. The optimum intensity is about one per cent of the intensity of the white light following a black stimulus.
5. A subnormal electrical excitability is seen for the first 7 sec. during presentation of a black patch in the light adapted eye. The electrical excitability returns then to the initial level spontaneously even when the black stimulus continues.
