The polychromatic theory

The effects on colour vision of adaptation to very bright lights

“…Since they do not, we must conclude either that the form of the sensitivity curve of at least one of the three kinds is altered by the adaptation, or that more than three kinds are active. Hartridge (1949), having reached the latter conclusion on other grounds, has used Wright's (1936) observation that colour matches can be upset by adaptation to support it. But the findings of the present detailed examination of the manner in which they are upset are much more easily explained on a basis of changes in sensitivity curves than on a polychromatic hypothesis.…”

“…A polychromatic theory such as that of Hartridge (1949), which denies the existence of a 3-class level and leaves the experimental fact of trichromacy unexplained, appears to require one of the same four ad hoc additional hypotheses, though the vagueness of Hartridge's theory concerning colour matching makes the argument (on the same lines as before, but replacing ' spectral sensitivity curves at the 3-class level' by 'the three functions of the receptor activities which determine whether two lights shall match') more abstract and less certainly exclusive of alternatives.…”

An opponent-process theory of color vision.

“…Why should the red and green hues in the spectrum predominate at low stimulus levels, and the yellow and blue hue components increase concomitantly as the spectrum is increased in luminance (43)? Why, as stimulus size is greatly decreased, should discrimination between yellow and blue hues become progressively worse than that between red and green (4,10)? Why should the hues drop out in pairs in instances of congential color defect, or when the visual system is impaired by disease (29,31)?…”