Calcium-dependent, background-induced acceleration of the dim-flash response kinetics. Mean (n = 4 retinas) normalized dim-flash responses (<20% of maximum response amplitude during each background) in darkness (black) and during different background lights (I_B 66 [dark cyan] and 664 [purple] R* s⁻¹ per rod) in normal (A and B) and low (C and D) Ca²⁺ solution. The dark-adapted response from C is also plotted in A (dashed red) for comparison. All traces in A–D have been digitally low-pass filtered with cutoff at 30 Hz, which did not affect dim-flash response waveforms. (E and F) t_p (mean ± SEM; n = 4) of dim-flash responses during background lights normalized to dark-adapted t_p,D of GCAP^−/− in normal Ca²⁺ as a function of background light intensity in normal (black) and low (red) Ca²⁺ for GCAP^−/− (E) and in normal (blue) and low (magenta) Ca²⁺ conditions for DKO (F) mice. Dashed lines plot the data from E for comparison. Error bars represent ± SEM.