Color vision processing in the primate visual system is initiated by absorption of light by three different spectral classes of cones. Consequently, color vision is described as being trivariant or trichromatic, and initial psychophysical studies demonstrated that colors could be matched by the use of three different primaries. In 1802, Thomas Young (1) proposed a model that perception of color can be coded by three principal color receptors rather than thousands of color receptors coding for individual colors.
Spectral sensitivity of cones can be determined through several methods. Two of these methods include isolating receptoral responses (2) using calculations from color matching function of normals and dichromats (a dichromat is a subject whose retina has one cone photopigment missing) (3), microspectrometry (4), or reflection densitometry (5, 6). The microspectrometer technique involves isolating a single cone and passing light through it. The change in transmission of different wavelengths can be used to calculate the spectral absorption of the cone or determine the change in electrical response. Reflection densitometry involves directing light in the retina and determining the change in absorption as a function of wavelength. These results are subsequently used to calculate spectral absorption.
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