Unique hue judgments as a function of test size in the fovea and at 20-deg temporal eccentricity

Abstract

Unique hue loci were measured for four observers in the fovea and at 20-deg temporal eccentricity as a function of test size. Eccentric measurements were made on the cone plateau following a rod bleach. The results indicate that unique yellow remains approximately invariant with respect to test size and retinal eccentricity, whereas unique blue and unique green shift to longer wavelengths with increasing test size. The locus of unique blue in the periphery reaches an asymptote at approximately the same wavelength as that from the foveal measurements, whereas unique green measured in the periphery is consistently at shorter wavelengths than in the fovea. In general, the data are best described by a model in which the short-wavelength-sensitive cone input to the two opponent-color channels decreases with decreasing test size and increasing retinal eccentricity.

Neurobiological hypothesis of color appearance and hue perception

“…This greatly increases the possible combinations of L- and M-cones in both the direct and indirect pathways. Accounting for all possible arrangements leads to a large shift in unique green towards shorter wavelengths similar in direction and magnitude to reports in the literature [62, 63] (Fig. 7).…”

L and M cone relative numerosity and red–green opponency from fovea to midperiphery in the human retina

“…However, a change in the relative number of L and M cones with eccentricity need not result in changes in red-green color appearance if compensating neural factors were to act to regulate color appearance across the retina. Experiment 1 was directed at the issue of whether, in the human eye, L and M cone relative numerosity varies with eccentricity from fovea to midperiphery, a region over which recent evidence [28][29][30][31][32][33] suggests that color vision is keen. Estimates were made of the relative number of L and M cones from fovea to midperiphery (Ϯ28 deg along the nasotemporal axis) in two color-normal observers.…”

“…However, recent psychophysical reports show that a full range of well-saturated hues can be observed in the extreme periphery, provided that the intensity and the size of the test stimuli are appropriately scaled with eccentricity. [28][29][30][31][32][33] In addition, the photopic luminous efficiency function does not vary with eccentricity if test fields are scaled according to the cortical magnification factor 24,34 ; this suggests stability in the relative number of L and M cones, because the foveal photopic luminous efficiency function is thought to be based on a linear combination of the L and M cone spectral sensitivities weighted by their relative number. [34][35][36] Estimates of the L-to-M cone ratio are stable from 28 deg nasal to 28 deg temporal eccentricity in two colornormal observers of this study.…”

Is discrimination enhanced at the boundaries of perceptual categories? A negative case

“…If the eye is adapted to daylight, then a line running obliquely in the diagram (from approx. 475 to 575 nm) divides chromaticities into reddish and greenish hues; and a second, superposed division into yellowish and bluish hues is made by a line that runs from approximately 520 nm to the white point and then nearly horizontally [4][5][6][7][8]. Chromaticities lying along the first of these boundaries comprise 'unique blues', 'unique yellows' and white (i.e.…”