Abstract

Color matches depend on the optical density and extinction spectrum of the cone photopigments. In addition it has been proposed that there is a physical effect of cone orientation on color matches (the Stiles-Crawford II effect). We have investigated this in ten observers by measuring (1) the retinal reflectance as a function of position in the pupil plan (the reflectometric version of the Stiles-Crawford I effect) and (2) Rayleigh color matches as a function of retinal illuminance. From the reflectometric data we calculate the position in the pupil and the spatial spread of the reflected light. From the color-matching data we calculate the optical density of the cone photopigments and the half-bleach illuminance. Both the optical density and half-bleach illuminance were significantly correlated with the spatial spread of the reflectance in the plane of the pupil. Observers with a smaller spread had higher densities (r = 0.82) and lower half-bleach illuminances (r = 0.67). Additional measurements of color matches for various pupil entry positions in two observers showed a strong dependence of the low illuminance match on pupil entry but not of the high illuminance (bleached) match. The half-bleach illuminance varied as expected due to the Stiles-Crawford I effect. These results are consistent with an optical density model of the Stiles-Crawford II effect. No additional wavelength dependent properties are required. The data also indicate that the variation in color matches in the normal population includes variation in the physical properties of the cones (e.g., the spread of cone orientations or cone apertures), as well as the optical density of individual cones and the extinction spectrum of the cones photopigments.

© 1991 Optical Society of America