Two distinct cone-opponent processes in the L+M luminance pathway

We measured phase shifts between Long-wavelength cone (L-cone) and Middle-wavelength cone (M-cone) signals as well as sensitivity in the luminance pathway either following a cone-silent substitution of colored background or on a steady colored background. In background substitution, the phase shifts between L- and M-cone signals varied only slightly depending on the substituted color, whereas marked elevation of the threshold following the substitution of colored background was found. In contrast, the phase shifts, as well as threshold, varied largely, depending on the background color in the steady background. These facts suggest that suppression by the cone-opponent process for background color substitution is different from the one for a steady colored background.