Figure 3. Background light decreases rod sensitivity and accelerates response decay.

A, mean peak response amplitude (± SEM) as a function of flash intensity for the cells of Fig. 2; colours indicate background intensity (in Rh^* s⁻¹) as follows: black, 0 (no background); red, 12; green, 32; blue, 122; orange, 330; and purple, 1190. Data for each background have been fitted with eqn (2) with the following values of r _max (in pA) and a (in Rh^{* −1}), from dimmest to brightest background: 13.1, 0.038; 11.6, 0.034; 10.6, 0.029; 8.8, 0.017; 5.8, 0.0083; 3.6, 0.0051. B, superimposed responses from Fig. 2 to the same flash of 31 Rh^* in each of the background illuminations; same colour coding as for A. Note monotonic decrease in response amplitude with increasing background intensity. C, superimposed responses from B normalized cell by cell to the same peak amplitude to illustrate acceleration of rate of response decay with increasing background illumination. Best‐fitting single exponential decay time constants (τ_rec) averaged cell by cell were as follows, from dark to background of 1190 Rh^* s⁻¹ in ms: 922 ± 18, 925 ± 20, 765 ± 9, 564 ± 12, 435 ± 10 and 364 ± 16. [Color figure can be viewed at wileyonlinelibrary.com]