CHROMATIC DISCRIMINATION WITH VARIATION IN CHROMATICITY AND LUMINANCE- DATA AND THEORY

Boynton and Kambe developed a model of chromatic discrimination in whi ch thresholds are mediated by two independent mechanisms: the short-wa velength sensitive (S-) cones (S-cone axis), and the middle-wavelength sensitive (M-) and long-wavelength sensitive (L-) cones (M/L-cone axi s). In this study, we used a Maxwellian view optical system to investi gate fundamental properties of the model as a function of chromaticity and luminance. We confirmed that discriminations along the S-cone axi s were dependent on S-cone excitation level. However, changes in chrom aticity and changes in mean luminance were not described by a single t hreshold-vs-radiance (TVR) template. We developed a model to account f or the different effects of changing S-cone excitation by varying mean chromaticity and by varying mean luminance. M/L-cone discriminations showed a minimum at the L-cone excitation to white, indicating strong opponency. The thresholds increased with luminance approaching a Weber region and showing parallel functions for differing chromaticities. T hese data are fit by a model allowing retinal gain controls and spectr al opponency.