Scotopic contrast hues displaced toward blue

Abstract.— Pre-stimulation with a neutral white light, in a dark-adapted state, produced a disposition for a scotopic hue of violet of about 463 nm. The observation may be explained on the basis of Helmholtz's theory of complementary negative afterimages, provided that (1) the assumption that neutral white is observed when the three types of cone receptors are activated to about the same degree, is rejected, and (2) the origin of the scotopic contrast hues is assumed to be located centrally to the photochemical systems of the receptors.