Red-green and yellow-blue opponent-color responses as a function of retinal eccentricity

Using the hue cancellation technique, I measured the spectral sensitivities of red-green (r-g) and yellow-blue (y-b) opponent-color responses of two color-normal observers at 0 (fovea), 3.3, 10, 21, and 31 degrees along the horizontal meridian of the temporal retina. The stimulus size as a function of retinal eccentricity was varied according to the cortical magnification factor. I found that the net spectral sensitivity (i.e. corrected for macular pigment) of the r-g channel was approximately constant as a function of retinal eccentricity. On the other hand, the net spectral sensitivity of the y-b channel was not constant. For the y-b channel I found a constant spectral sensitivity as a function of eccentricity when no macular correction was made. This means that the y-b system changes its yellow and blue responses with eccentricity to counterbalance the effects of macular pigment.