The photoreceptor membrane characteristics at different light adaptation levels. The photoreceptor impedance, Z, (f) calculated from the current injection and the resulting voltage responses, is reduced (A, gain), it is accelerated (B, 3-dB cut-off frequency) and it lags the stimulus less (C, phase) when it is shifted towards higher frequencies with increasing light adaptation. Regardless of the adapting background the membrane operates linearly over the studied frequency range (in D,γ_exp²(f) and in E,γ_SNR²(f); coherence close to unity). Both the normalized impedance (F) and the gain of the contrast-induced voltage responses (i.e., light response), (G) demonstrate a gradual shift of their bandwidth towards high frequencies. The cut-off frequency of the impedance is always much higher than that of the light responses in the same photoreceptor at the same adapting background; in this particular photoreceptor, 3.1, 1.9, 3.2, 5.1, and 4.2 times higher, when going from BG-4 to BG0.