Dichromatic color vision at high light levels: red/green discrimination using the blue-sensitive mechanism

Three red/green blind observers (dichromats) performed a wavelength discrimination task over a wide range of intensity levels. As expected, discrimination failed in the entire red/green spectral range at the low intensities typically used in wavelength discrimination experiments, but at very high intensities (at or above 10,000 td) discrimination was well maintained into the red/green range. The following experiments demonstrate that dichromats are able to utilize signals from the blue-sensitive cones (S-cones) to mediate color discrimination throughout the spectrum at high intensities, and they provide an estimate of S-cone sensitivity throughout the visible spectrum.