Effects of chromatic adaptation on opponent interactions in monkey increment-threshold spectral-sensitivity functions.
The effects of chromatic adaptation on the opponent interactions of cone mechanisms were investigated by using increment-threshold spectral-sensitivity (ITSS) functions and threshold-versus-radiance (TVR) curves in rhesus monkey subjects. The TVR curves showed shape- and field-sensitivity invariance for both 580- and 500-nm adapting backgrounds and indicated that three cone mechanisms were mediating detection over moderate adapting-field intensity levels. Differential adaptation between the long-wavelength-sensitive (L) and the middle-wavelength-sensitive (M) opponent (L - M) and nonopponent (L + M) channels and the short-wavelength-sensitive (S) channel caused changes in the shape of the ITSS function as the adapting-field intensity was increased without changes in the level of cone interaction. Chromatic adaptation also resulted in significant changes in the shape of the ITSS functions, but it still exhibited characteristic L-M opponent interactions. Converting ITSS data to cone-contrast coordinates for R-G adapting fields indicated that the relative contribution of the L and M cones at the second site was approximately equal (detection contour slope approximately 1). Consequently, most of the changes in the shape of ITSS functions under chromatic adaptation are explained by the von Kries adaptation principle. ITSS functions on a green background also exhibited opponent interactions between S cones and longer-wavelength cones. The cone-contrast coordinates, when expressed for S cones, showed that the inhibitory interactions occur because the S-cone signal subtracts from both M and L cones.