Scotopically equated stimuli versus photopically equated stimuli in unique hue judgments

Abstract

One of the quandaries when studying color perception in the peripheral retina is whether to equate stimuli photopically to the cones or scotopically to the rods. Both methods are prevalent in the literature and while many of their findings are similar, there are some notable differences. The purpose of this study is to determine whether the differences in results can be at least partially attributed to the methodology used to equate the stimuli. Unique hue loci (blue, green, yellow) were measured in the fovea and at 10° temporal retinal eccentricity under bleach and no-bleach conditions for stimuli equated either photopically (0.3 and 2.3 log phot td) or scotopically (1.0 and 3.0 log scot td). Resultant unique hue loci were then converted to a common intensity unit for ease of comparison. Results demonstrate clear differences between unique hue loci determined with scotopically equated stimuli versus photopically equated stimuli, (e.g. in locus, scalar invariance, and the pattern between bleach and no-bleach conditions) which may account for some of the discrepancies found in the literature. Thus, different laboratories may draw dissimilar conclusions regarding retinal mechanisms mediating peripheral color vision based partially on the manner in which the data were collected.