Abstract
With changes in intensity and duration of light, the retinal potential undergoes slight changes in form, while the nerve discharges show transformations corresponding to the form of the stimulus.
The fore part of the rabbit's brain was removed under ether, exposing the optic nerves. Records were taken from one nerve and from across the corresponding retina. Light intensities used were high but within the physiological range, as indicated by reduction of response with reduction of intensity. Experiments were conducted in a dark room, flashes being delivered at about 1 per second from a 2-mm slit in the lamp housing, in front of which a sector disk was rotated. A lens projected an image of the slit on the rabbit's cornea, the eye thus focused an image of the lens on the retina. This image stimulus was compared with one from a diffusing screen close to the cornea illuminated with a 1 ¼-inch spot of light.
With flashes as short as 5 ms the retinal potential shows the usual a wave, a diphasic b wave, and no c. The “off” effect does not appear. With longer durations the b wave assumes its conventional monophasic form which does not return to the base line during illumination. (Fig. 1.) Between 5 and 200 ms duration, and between 18,000 and 200 candles per sq ft, the form of the retinal b wave changes surprisingly little.
On the contrary, the nerve discharge alters progressively over these ranges. The characteristic “on” response to a short bright flash occurs in two parts, the first consisting of a sharp initial spike followed usually by a decreasing series at 10-ms intervals, and the second, a rise which falls off during further illumination, its peak at about 30 ms after the first.
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