Abstract
Spectral sensitivity varies markedly between the fovea and near periphery due to cone sampling density changes and the rapid fall off in macular pigment density with eccentricity. Neutral white settings show complete compensation for these sensitivity differences (Beer et al. JOV 2005), while perceived hues have instead been found to vary and have been attributed to a partial compensation for macular pigment along the blue-yellow dimension (BY) of color appearance (Hibino, Vision Research 1992) or to relative losses in signal strength along the red-green dimension (RG) (Parry et al JOSA 2006). We measured both achromatic points and unique and binary hue loci to explore the extent and form of color appearance changes in the periphery. Stimuli were 25 cd/m2 2-deg circles displayed on a black background or an isoluminant gray adapting background equivalent to equal-energy white. The stimuli were shown for 0.5 sec at 4 sec intervals and were viewed directly or at an eccentricity of 8 deg. White settings were measured with a method of adjustment and were similar and thus effectively compensated at the two locations. Hue loci were measured with a 2AFC staircase that adjusted the stimulus angle at a fixed contrast relative to the nominal white. Hue loci differed across location and observers but were not clearly more variable for RG than BY or for unique vs. binary hues. We compare the pattern of these hue changes to the variations predicted from measures of each observer's macular pigment density difference between locations, and also examine the role of the common gray adapting background in normalizing hue settings and how this influences interobserver variations in color perception. These results are important for understanding the ways and extent to which color percepts can be calibrated to reflect consistent properties of the stimulus or are limited by physiological constraints.