Simulated bipolar cells in fovea of human retina

Abstract

Effects of chromatic adaptation on C-type bipolar cells (BC) in human retinal fovea are studied. Adaptation of the r-g channel is linear for both central fovea and parafovea. Adaptation of the parafovea bl-y channel, on the other hand, is nonlinear, which is accounted for by the slower adaptation rate of blue-sensitive cones with white light intensity as compared to rates of red- and green-sensitive cones. Achromatic adaptation of red- and green-center BCs produces uniform response decreases but without unique yellow loci shifts. Achromatic adaptation of blue-center BCs, on the other hand, does cause shifts of the unique green locus. Shifts of the crossover points for the BC response spectra occur with chromatic adaptation; the unique yellow loci shifts to shorter wavelengths with adapting wavelengths shorter than 550 nm and longer wave-lengths with longer adapting wavelengths than 550 nm. Chromatic adaptation is sufficient to explain the Bezold-Brüke effects; but to fully account for these shifts a novel hypothesis is proposed. For the green and red spectrum regions Bezold-Brücke shifts are due to r-g channel chromatic adaptation, while for the blue spectrum region bl-y channel chromatic adaptation accounts for Bezold-Brücke shifts. The two channels function independently in an either/or manner. The bl-y channel, besides having a unique green locus at 517.7 nm, has a crossover point at about 670 nm. Chromatic adaptation of the bl-y channel produces shifts of the unique red locus, which may account for extraspectral hue shifts.

Color Perception of Aperture Colors Using a Computational Model of the Human Visual System

“…As discussed previously [1], the ratio of L-to M-cones can vary widely from 2.1 to 0.6. The most commonly accepted ratio of L-to M-cones based on psychophysical data is 2 [11].…”

“…The foveola is free of S-cones [1] and may be as low as 3-6% in the remaining fovea increasing to as high as 20% in the parafovea. Procion yellow stained cells (S-cones) form an approximately rectangular array with an intercone distance of 6 min of visual angle or 12 cones [16].…”

“…The most commonly accepted ratio of L-to M-cones based on psychophysical data is 2 [11]. However, initially seven types of L-and Mcone matrices were studied [1], which included fixed geometry types with L-to M-cone ratios of 1, 2, and 3. Also included were randomly organized matrices with L-to M-cone ratios of 1, 2, and 3.…”

“…Also included were randomly organized matrices with L-to M-cone ratios of 1, 2, and 3. Based on resolution studies [4,5] and preliminary studies with color coding, it was decided that a L-to M-cone ratio of 1 gave the best results in terms of resolution and color coding.…”

“…Details of the human fovea model as well as ancillary functions including stimuli, light sources and use of Fourier analysis have been described elsewhere [1][2][3][4][5][6][7][8]. Nevertheless the model has been sufficiently modified and new features added that it seems justified to describe the present model for color perception.…”