Abstract
The hues of most wavelengths change when a desaturating light is added, a perceptual nonlinearity known as the Abney Effect. Mizokami et al (JOV 2006) proposed that these hue shifts reflect compensation for filtering effects imposed by the eye's spectral sensitivity so that constant hues are tied to constant inferred properties of the stimulus (e.g., the mean of inferred Gaussian spectra). We evaluate this hypothesis by testing whether individual differences in the size and form of the Abney Effect can be accounted for by individual differences in spectral sensitivity. Stimuli were uniform 2-deg fields presented in an integrating sphere and generated with an OL 490 Agile Light Source (Optronic Laboratories), which allows the spectrum of the light to be shaped in arbitrary ways. Conventional Abney Effects were assessed by varying the proportion of a flat spectrum added to fixed narrowband spectra, with peak wavelength adjusted in a 2AFC staircase to match hues across different purities. These settings are compared to results for Gaussian spectra that are matched in chromaticity to the Abney spectra. The observer's spectral sensitivity was measured in the same device with flicker photometry. Individual differences in spectral sensitivity (e.g., because of greater lens or macular pigment density) predict measurably different hue shifts to compensate color appearance in different observers. We model these predicted hue shifts for normal variations in observers and compare them to empirically determined constant-hue loci. Changes in the Abney Effect are also predicted between the fovea and periphery (e.g., because of changes in macular pigment density) and thus we also compare the hue shifts at different eccentricities. These analyses help to reveal the stimulus correlates of hue percepts and the extent to which these percepts can be corrected for the spectral filtering effects specific to an individual's eye.