Figure 5. Linearity of macroscopic flash response.

A, the average flash (impulse) response to 5 brief (1 ms) flashes containing ca 75 photons (continuous line) is compared to the average response to 64 flashes each containing, on average, 0.9 photons (dotted trace) and scaled according to the difference in intensity (×83). The close overlap confirms the linearity of the response over this intensity range. B, peak responses to brief (10 ms) flashes of increasing intensity. Data from 3 different cells were all well fitted by a linear relationship (2.9 pA per effective photon). A simple linear correction was applied for the calculated series resistance (R_s) errors (R_s× total current; maximum error ca 10 mV) assuming a reversal potential of +12 mV. C, the latency dispersion measured directly from flash bumps recorded in the same cell (histogram) is compared to the latency dispersion predicted by deconvolving the average bump waveform from the impulse response (continuous curve, see Methods). Normalized time courses of the average bump (dotted trace) and impulse response (continuous trace) are shown below. Data are from a single WT photoreceptor under control conditions; similar analysis was performed in 7 cells.