Figure 6.

Distributions of M and S weights differed between different retinal areas but were similar across cell types.A, Cone weights of horizontal cells estimated from flicker data. To estimate cone weights, we included rod input in the analysis, fixing the rod weights at the mean level measured in the flash experiments at the same background intensity and retinal region (green dots and circles in Fig. 3A). The resulting estimates are shown as green dots and circles in the present figure. We also estimated cone weights under different assumptions about rod input. Additional rod weights assumed were no rod input (gray) and ±1.5 SD away from the mean estimate (red and blue). In the fits, we constrained the cone weights to be positive, which, for some cells, altered the rod weight to a smaller value when derived M or S weights equaled 0. The rod weights shown in the insets are the mean values used in calculations, which are smaller than the nominal values because of the alteration procedure described in the previous sentence. Across the range of rod weights assumed, clear separation of the data from superior and inferior retina holds. The background produced 4.16 (M), 4.12 (S), and 4.76 (rod) log₁₀ Rh*/photoreceptor/s. All panels used the same background.B, Comparison of mean cone weights from A with those from the horizontal cell flash data and cone opsin ratio estimates from immunostaining. Both panels plot M and S weights as fractions of total cone input. Error bars (indicating SE) are plotted only for M cones. Bars marked with squares summarize data in A. For horizontal cells in superior retina, assuming higher rod weights leads to a higher fraction of M versus of S input and vice versa in inferior retina. The effect of varying assumed rod weight is small relative to the effect of retinal location. Bars labeled Flash H represent cone weights obtained for horizontal cells in the flash experiments. For superior retina, the bar labeled Immuno represents the fraction of M and S cones of all cones, which we also take as the opsin ratio. Inferior retina lacks this bar because immunostaining could not quantify the ratio of M- to S-opsin expression. Qualitatively, S-opsin expression greatly exceeds M-opsin expression in inferior retina.C, Cone weights of ganglion cells estimated from flicker. The same format as A is shown. Results from horizontal and ganglion cells are similar.D, Summary of cone weights in C. The same format as B is shown. For ganglion cells, in superior retina, assuming higher rod weights leads to a higher fraction of M input versus that of S and vice versa in inferior retina. The effect of varying rod weight is small relative to the effect of retinal location. Together with B, the plot establishes that the cone weights from the flicker are similar for horizontal and ganglion cells and are consistent with cone weights from the flash data for horizontal cells and the opsin ratio obtained from immunostaining.