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. (C) 1998 Elsevier Science Ltd. All rights reserved.