Chromatic adaptation and π mechanisms

Adaptive hue shifts of the achromatic point were measured in conditions in which a test field was presented as a flashed increment on steady chromatic backgrounds. The variables investigated were background chromaticity, luminance, and stimulus contrast. The results could be accounted for quantitatively by a mechanistic model with the following properties: discounting of the (steady) background, or ac‐coupled signal processing; cone spectral sensitivities as estimated by Vos and Walraven; and receptor‐specific gain controls that have the same action spectra and gain characteristics as Stiles' π₅, π₄, and (modified) π₁ mechanisms.