The time-dependent variance of the single-photon responses in wild-type, Arr1+/−, GRK1+/− and GRK1+/−Arr1+/− rods. Left panels superimpose 10 isolated single-photon responses from a wild-type and a Arr1+/− rod (A), a GRK1+/− rod (B), and a GRK1+/−Arr1+/− rod (C). Right panels compare the squared mean (thin trace) and the time-dependent variance (thick trace) of wild-type rods (gray, n = 29) with Arr1+/− (red, n = 41) rods (A), GRK1+/− (blue, n = 30) rods (B), and GRK1+/−Arr1+/− (green, n = 40) rods (C). The responses in each cell were normalized by the amplitude and time-to-peak of the cell's average single-photon response to facilitate comparison of the time course of the variance.