The involvement of rod photoreceptors in dark adaptation

From analysis of previously reported scotopic dark adaptation curves (Pugh, 1975b), evidence has been found for the existence following a bleach of three separate components in the decline of the "equivalent background intensity", with decay time constants of about 5 sec, 100 sec and 7 min. The results are consistent with the idea that the equivalent background is caused by photon-like events in the rods as a result of intermediates produced by the bleaching light, and a model of the removal of these intermediates provides a good description of the psychophysical results. The ideas are consistent with the recent demonstration of an increased rate of occurrence of quantal events in rods following a bleach (Lamb, 1980).