Figure 3.

Area summation curves for the different response components. Response amplitude for modulated spots (A) or annuli (B) for a representative MC cell. Luminance (30% contrast) or |M – L| chromatic modulation responses (30% RMS cone contrast, R/G ratio adjusted to each cell's 1^st harmonic null) are shown. 5 Hz modulation, 32 cycles. Amplitude and phase (not shown) were fitted as described in the text (solid lines). Free parameters of interest are achromatic center and surround sizes (σ_c, σ_s) and size of the chromatic field (σ_chr) generating the 2F response. (C, D) These parameters (σ_c, σ_s, σ_chr) are plotted against eccentricity in C for an MC cell sample and fitted with the linear relations shown. The 2F chromatic response field (σ_chr) is of intermediate size to achromatic center (σ_c) and surround (σ_s). (D) Size of achromatic surround (σ_s) and chromatic 2F field (σ_chr) plotted against achromatic center radius (σ_s), with linear regression lines. Data are again consistent with a mechanism larger than the achromatic center (σ_c) but smaller than the achromatic surround (σ_s).