Duplicity Theory of Vision: From Newton to the Present

116 chromatic rod vision: a historical account700600Wavelength (nm)500400400500600 700Wavelength (nm)Fig. 12.2 Scotopic contrast hues (○) together with additive opponenthues (● ). Abscissa represent wavelength of pre-stimulation while theordinate represents wavelength of scotopic contrast hues. The fieldsubtended 1 × 2° and was applied 6° temporally to the fovea.12.4 Scotopic hues explainedThe conclusion opposed the basic assumptions of the Young-Helmholtzcolour theory that the different receptor types functioned independentlyof each other, and that each receptor type mediated one colourquality only (see Helmholtz, 1896). The trichromatic colour theory,therefore, had little to offer as a theoretical basis of the scotopiccontrast colours.The question, then, arose of whether the conclusions couldbe explained more easily within the framework of Hering’s (1878)opponent colour theory.Hering had realized that colour vision must involve opponentcolour processing somewhere in the visual pathway, but his phenomenologicalapproach did not allow any conclusion as to the site of theantagonistic interactions. Three quarters of a century later, however,