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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

Is the binocular rivalry mechanism tritanopic?

Binocular rivalry for a series of colored targets was measured in three trichomats and two red-green dichromats by cumulating those times when ony one target or the other was perceived (exclusive visibility time). Targets were black and colored 3 c/deg square-wave gratings, 1 degree in diameter. For trichromats, exclusive visibility time increased as a function of color difference between the targets, but for dichromats there was no effect of color on binocular rivalry. Taken together, these data indicate that the binocular rivalry mechanism is tritanopic: it is responsive to color signals only from the medium- and long-wave-sensitive cones.

Color↗
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↗
PubMed1983

Densitometric measurement of human cone photopigment kinetics.

We measured the radiance response function for steady state bleaching lights and the regeneration of the cone visual photopigments using the continuous recording densitometer described by v. Norren and v.d. Kraats. Measurements made on 5 deuteranopes, 1 protanope and 2 color-normal observers were similar. The radiance response function was steeper than the function predicted by a simple first-order kinetic equation. For a measured density (ca 0.3) we evaluated whether high stray light (ca 47.5%) and high two-way optical density (ca 1.3) could account for the deviation from the prediction of a first-order equation. Such a model was rejected because these parameters predicted different estimates of the time course of regeneration for different test wavelengths (554 and 605 nm). Statistical analysis of the regeneration data revealed a highly significant non-linearity. A model in which the rate of regeneration increases as the proportion of bleached photopigment decreases is required to explain both the radiance function and the regeneration data.

Adult↗