Figure 2.

Pepperberg plots for WT rods in darkness and in the presence of background light. A, B, We show mean responses to five 20 ms flashes each for the same nine rods in darkness (A) and in the presence of a steady background intensity of 1350 photons μm⁻² s⁻¹ (B) for the same series of eight flash intensities of 453, 646, 863, 1120, 1870, 2430, 3250, and 4430 photons μm⁻². The interval between flashes was 7 s. The horizontal line marks the level of 75% of peak response amplitude. C, Plot of time in saturation as a function of flash intensity for the rods of A and B. For each rod at each flash intensity, we measured the time between the beginning of the flash and the recovery of the photocurrent to the value indicated by the horizontal lines in A and B; this is equivalent to the time necessary to reopen 25% of the channels. These values (T_sat) were plotted as a function of flash intensity in darkness (filled squares) and in the presence of the steady 1350 photons μm⁻² s⁻¹ background (open squares). Error bars are SE. The lines drawn through the data are the best linear fits and give estimates of the rate-limiting time constant τ_D; these are 231 ms in darkness and 170 ms in the background. D, Plot similar to C but for a different group of seven rods in darkness and at a background intensity of 4090 photons μm⁻² s⁻¹. Linear fits give estimated values for τ_D of 168 ms in darkness and 78 ms in the background.