Sensitivities of color-normal observers to temporal variations in stimulus luminance and chromaticity were measured for sine-wave stimuli between 1.5 and 20 Hz. Clear differences were found in observers' sensitivities to isochromatic luminance variations and to isoluminous chromaticity variations for wavelength pairs selected to test temporal discriminability along the red-green and yellow-blue dimensions, respectively. Despite interobserver differences in individual red-green functions, a given observer's sensitivity could be described by a single curve shape specific to that observer. Overall sensitivity for yellow-blue was less than that for red-green for all observers. Differences in curve shape between red-green and yellow-blue functions are found for individual observers, but group averages reveal that the differences are not systematic. Red-green temporal sensitivity is largely unaffected by adapting backgrounds in red-green equilibrium but is attenuated at low frequencies by nonequilibrium backgrounds of the same luminance. Isochromatic luminance sensitivity is largely independent of our adapting backgrounds, but heterochromatic luminance modulation functions undergo expected changes in form.

Color↗

PubMed1982

Gunnar Svaetichin: man of vision.

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Animals↗

PubMed1979

Receptoral and postreceptoral visual processes in recovery from chromatic adaptation.

The time course of recovery from chromatic adaptation in human vision was tracked by determining the wavelength of light that appears uniquely yellow (neither red nor green) both before and after exposure to yellowish green and yellowish red adapting lights. Recovery is complete within 5 min after steady light exposure. After exposure to the alternating repeated sequence 10-sec light/10-sec dark, the initial magnitude of the aftereffect is reduced but recovery is retarded. The results are interpreted in terms of two processes located at different levels in the hierarchical organization of the visual system. One is a change in the balance of cone receptor sensitivities; the second is a shift in the equilibrium baseline between opposite-signed responses of the red/green channel at the opponent-process neural level. The baseline-shift mechanism is effective in the condition in which repeated input signals originating at the receptors are of sufficient strength to activate the system effectively. Hence, this process is revealed in the alternating adaptation condition when the receptors undergo partial recovery after each light exposure, but receptor adaptation during continued steady light exposure effectively protects the subsequent neural systems from continued strong activation.

Color↗

PubMed1978

Dichromatic color language: "reds" and "greens" don't look alike but their colors do.

When protanopes or deuteranopes arrange the Farnsworth Dichotomous Test colors in order of similarity, they reveal their lack of red/green hue discriminations by alternating chips that the normal trichromat sees as reddish and greenish test colors. The dichromatic orderings follow a systematic variation in saturation of blue hues through neutral and into yellow hues as described by theory for each of the two types. Some dichromats who show the typical test behavior nevertheless use reddish and greenish hue terms appropriately when instructed to name the same test colors. Lightness cues are probably used by these dichromats in the naming task but ignored in the perceptual similarity task. Thus, unlike normal trichromats, who use similar names for perceptually similar colors, dichromats may use dissimilar names for perceptually similar colors. In this way they can achieve concordance with the normative language system despite its discordance with their impoverished color perceptions.

Color Perception↗

PubMed1977