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PubMed1981

Foveal tritanopia.

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Adaptation, Ocular↗
PubMed1982

In search of the elusive long-wave fundamental.

Action spectra for threshold detection of flicker (30 Hz) were obtained on 11 deuteranopes under carefully controlled adaptation conditions. Individual differences were large, so that each one of the long-wave fundamentals proposed by different theorists finds reasonable justification in the spectrum measured on at least one deuteranope. Some deuteranopes' spectra are not described by any one of these "fundamentals". To a first approximation at least, trichromats' spectra show the property of linear additivity. One such trichromat's spectrum agreed well with that of a deuteranope with whom he shares a common erythrolabe, and appears to be uninfluenced by his chlorolabe-filled cones.

Color Perception↗
PubMed1982

What causes trichromacy? A theoretical analysis using comb-filtered spectra.

For colour vision, the task of the eye is to discriminate different distributions of energy over the spectrum. This is usually treated as a problem in the wavelength domain, analogous to treating spatial resolution in terms of spatial positions in the image. What is attempted here is a treatment of colour vision in terms of the system's responses to spectral energy distributions that are sinusoidal functions of wavelength. These are called comb-filtered spectra, and the treatment is analogous to that of spatial vision in terms of spatial sinusoids. This gives some insight into the reasons for trichromacy, the advantages of oil droplets, and the narrow separation of the red and green mechanisms. It is also shown that the absorption spectra of photosensitive pigments are superimposable if plotted as a function of the fourth root of wavelength.

Color Perception↗
PubMed1982

Post-receptor chromatic mechanisms revealed by flickering vs fused adaptation.

For both normals and dichromats, adaptation to certain pairs of alternating monochromatic caused reduced sensitivity for detection of some test wavelengths when compared to sensitivity losses caused by adaptation to the fused (supra-CFF) sums of the same lights. Since the two adaptation conditions caused equivalent photopigment depletion, and since sensitivities to some wavelengths did not differ between conditions, the effects are ascribed to post-receptor adaptation. Such post-receptor effects were not obtained when adapting wavelengths did not straddle the presumed "crosspoints" of opponent-colors mechanisms, and, when only one opponent mechanism was adapted, effects were absent for test wavelengths at the crosspoint of that mechanism. For the red vs green system, increasing the intensities of adapting wavelengths from 2.2 to 5.5 log td did not appreciably increase the magnitudes of postreceptor effects. Quantitative accounts for the results are derived from a vector model for color vision. The results provide general support for opponent-colors interpretations of normal and dichromatic vision and suggest that the flicker/fused adaptation paradigm is a useful tool for probing postreceptor mechanisms of vision.

Adaptation, Ocular↗
PubMed1984

Color-vision mechanisms of the extrafoveal retina.

Wavelength discrimination, spectral sensitivity as well as color-matching performance were measured at the fovea and at different eccentricities in the peripheral retina. The results show that the underlying mechanisms of color vision in the normal peripheral retina are different from those of the classic forms of congenital color blindness. On the other hand, a close correspondence was found between color-vision characteristics obtained in the extrafoveal retina and in patients with acquired color-vision defects due to diseases of the optic nerve, suggesting that the loss of color discrimination with eccentricity and during progression of these diseases has a common underlying basis.

Color Perception↗
PubMed1984

The influence of cones on rod saturation with flashed backgrounds.

The increment threshold for a middle-wavelength test flash was measured at the onset of a concentric long-wavelength background flash under conditions that have previously been shown to result in rod system saturation. The influence of the cone system on rod saturation under these conditions was assessed using the Stiles-Crawford effect in normal subjects and by measuring rod thresholds in protanopes, who are deficient in long-wavelength cones. When the background flash is made less effective for cones through the Stiles-Crawford effect, the onset of rod saturation occurs at a higher luminance of background flash than normal. Similarly, protanopes do not show the characteristics of rod saturation until a much higher-than-normal luminance of background flash. The results suggest that rod system saturation with flashed backgrounds is strongly influenced by cones.

Adaptation, Ocular↗
PubMed1984

Temporal integration of the pi 1/pi 3 pathway in normal and dichromatic vision.

Stiles' pi 1 and pi 3 mechanisms are thought to reflect adaptation events at two sites in a single pathway, the first site controlled by the short-wavelength cones alone, the second site controlled by opposing signals from these cones vs the other cone classes. We examined this pathway's temporal integration under conditions that yield the full gamut of possible adaptation states at the two sites. Critical duration of the pi 1/pi 3 pathway was always about 200 msec. In addition, we examined the pi 1 and pi 3 mechanisms of dichromatic vision. Our results suggest that protanopic and deuteranopic vision are characterized by a pi 1/pi 3 pathway similar to that in normal color vision.

Color Perception↗
PubMed1985

Just noticeable inhomogeneity criterion for determining wavelength discrimination functions.

The visual criterion of just noticeable inhomogeneity is described for determining wavelength discrimination functions. It involved determining the wavelength differences between reference and test fields required to produce a just noticeable inhomogeneity which cannot be eliminated by a brightness adjustment. The fields formed a checkerboard pattern the element size of which variable. Tritanopic delta lambda functions were obtained by using the small field insensitivity of the fovea. Just noticeable border, data obtained from bipartite field studies, were replicated with this checkerboard field.

Color Perception↗
PubMed1985

Characterization of the color related receptor mosaic in the ground squirrel retina.

Light microscopic and histochemical studies reveal that the retina of the European ground squirrel (Citellus citellus L.) contains a mosaic pattern of two cone types and a small population of rods. A minority (7%) of the cones can be characterized by their ellipsoids having larger diameters and increased staining density over the majority population. Exposure to green light selectively elicited intense NBT-diformazan labeling in the major population of cones while the larger diameter cone type was labeled after blue illumination. The two cone subpopulations are probably the blue and green cone types of ground squirrel protanopic color vision.

Animals↗