General comparison of the transduction signal and noise and membrane bandwidth at different adapting backgrounds. (A–C) The dynamics of the corresponding light current, voltage response, and membrane impedance displayed as their normalized gain. (A) Under dim conditions, the light current is noisy and the low passing membrane removes the high frequency noise, producing slow voltage responses to light contrasts. When the mean light intensity is increased, both the transduction cascade and photoreceptor membrane allows faster signaling leading to accelerated voltage responses (B and C). The corresponding impulse responses (D), calculated from the same data, show how the light current and voltage responses quicken with increasing mean light intensity, but the light current is always peaking before its respective voltage response. Because of the large membrane impedance under dim conditions, the small light currents can charge relatively large voltage responses. The responses are normalized by the maximum value of each series. (E–G) The transduction bump noise, |ΓI˜(f)|, was calculated by deconvolving the photoreceptor membrane impedance, Z(f ), from the respective voltage bump noise, |ΓV˜(f)|. From dim light conditions (E and F) to the bright adapting backgrounds (G) |ΓI˜(f)| shows a considerable overlap with the corresponding membrane impedance.
