Characteristics of the electroretinogram (ERG) produced by the essentially all rod eye of the rat are presented as functions of the number of quanta absorbed by each rod per stimulus flash. The ERG's were obtained with 1.5 msec. stimulus flashes and uniform illumination of the entire retina. Under these conditions, distortions in the ERG due to stray light are minimized, and the ERG more accurately reflects the activity of its retinal sources. The effects of background light and two forms of dark adaptation were studied and compared. The results, especially for the b-wave, permit an interpretation in terms of two distinct processes. One process appears to determine the b-wave latency. This process is almost independent of the state of adaptation of the retina. The other process does not affect the latency, but determines the b-wave threshold and amplitude. This process strongly depends upon the state of adaptation. Moreover, the effects of dark adaptation on this amplitude-determining process are almost identical with the effects of background light.

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