Spectral sensitivity of single cones in the retina of Macaca fascicularis.

Colour vision depends on the wavelength-dependent absorptions of three different photolabile pigments each located in a particular type of retinal cone. The spectral absorption of primate cones has been examined by microspectrophotometry, but this method gives information only at wavelengths where the absorption is relatively strong. Here we have analysed the absorption of two of the cones over a wider range of wavelengths by recording their electrical responses to monochromatic light. The observations were made on the retina of the monkey Macaca fascicularis, an animal thought to have cone pigments like those of man. The measured spectral sensitivities of the red-sensitive ('red') and green-sensitive ('green') cones agreed well with estimates of the cone pigment absorptions derived from colour-matching experiments in humans. At long wavelengths the sensitivity of the red cones was found to decline more rapidly than that of the green. This behaviour, attributable to the cone pigment molecules themselves, explains the paradoxical hue shift, in which a light of very long wavelength is perceived to be identical to a light of shorter wavelength.