(a) (b) (c) Rho value as a function of retinal eccentricity for single-entry measurements, ρs (filled circles); multiple-entry measurements, ρm (filled squares); and Stiles-Crawford effect measurements, from He et al. (1997)14, ρSCE (filled triangles). Subjects JH (a), SM (b) and SB (c). The variation of ρm and ρSCE with retinal eccentricity is similar; both increase more slowly with increasing retinal eccentricity than ρs. However SCE measurements are still broader than multiple-entry measurements. (d) Rho value as a function of wavelength for subject JH: ρs (open circles); multiple-entry measurements, ρm(open squares); and Stiles-Crawford effect measurements, ρSCE (open triangles). ρs decreases markedly with wavelength, whereas ρSCE and ρm do not change significantly. Error bars represent !1 standard error of the mean.