Figure 5. Contrast gain of midget and parasol cells.

A, Contrast-response functions for simultaneously recorded OFF midget and OFF parasol RGCs. Data from two preparations are shown in separate rows. Peak firing rates are shown from responses to 250 ms steps of light of increasing contrast presented in single cone stimulation regions (see Fig. 2). Each trace represents responses of a single midget (solid lines with circles) or parasol (dashed lines with triangles) cell to stimulation of a single cone. B, Estimated contrast-response of cells in (A) to stimulation of the full receptive field center, obtained by scaling the contrast-response curve measured for a single cone by its fractional cone input strength, obtained from receptive field maps (see Experimental Procedures). Linear fits are plotted for the collection of midget (heavy solid line) and parasol (heavy dashed line) cells. C, Distribution of contrast gains in individual midget and parasol cells, estimated from the slopes of linear fits to each trace in (B). Inset replots the contrast gain distribution of putative midget and parasol cells in response to drifting sinusoidal gratings (Kaplan and Shapley, 1986).