Fig. 13.

Intensity dependence of background desensitization in a green cone. Points plot peak flash sensitivity to a 500 nm test flash (S_L), normalized to the dark-adapted sensitivity (S_D) as a function of the intensity of a 500 nm background light (I_B). Some of the responses used for these data are shown in Figure 12. S_L andS_D were compared in interleaved trials; no significant reduction in S_D was observed between trials. A, B, Points (•) plot normalized sensitivity at the peak of the response. The solid curve in A is the least-squares fit of the points to a Weber–Fechner function (Eq. 2) withI₀ = 10,600 photons μm⁻² sec⁻¹. The solid curve in B is the weighted sum of two Weber–Fechner functions given by Equation 3 with α = 0.75,I^R₀ = 70.8 photons μm⁻² sec⁻¹, andI^C₀ = 27,300 photons μm⁻² sec⁻¹. The putative rod and cone contributions that comprise the weighted function are plotted by the dashed and dotted curves, respectively. C, Points (○) plot normalized sensitivity measured at 300 msec. The solid curve is the least-squares fit of the points to a Weber–Fechner function (Eq. 2) withI₀ = 84 photons μm⁻²sec⁻¹.