Kenneth Fuld

Sex Differences in Macular Pigment Optical Density:: Relation to Plasma Carotenoid Concentrations and Dietary Patterns

Sex differences in macular pigment (MP) optical density (measured psychophysically) were examined. Concentrations of lutein and zeaxanthin (L and Z) (non-separated) and beta-carotene (BC) in the blood were determined using reverse phase high-performance liquid chromatography. Dietary intake of L and Z, BC, fat, and iron were estimated by questionnaire. Males had 38% higher MP density than females (P < 0.001) despite similar plasma carotenoid concentrations and similar dietary intake (except for fat). Dietary intake of carotenoids, fat and iron, as well as plasma concentrations of L and Z were positively related to MP density in males. Conversely, only plasma L and Z was related to MP density for females, and dietary fat was negatively related to MP density. Sex differences in protection of the retina by MP and in the relationship between the retina, blood and diet could be a factor in the incidence of retinal diseases, especially age-related macular degeneration.

Macular pigment optical density and photophobia light threshold

Light absorption by macular pigment may attenuate visual discomfort, or photophobia, for targets composed of short-wavelength light. Macular pigment optical density (MPOD) and photophobia light thresholds were measured psychophysically in 10 subjects. The energy necessary to induce photophobia for a short-wavelength target relative to a long-wavelength target was linearly related to MPOD, as well as estimates of peak MPOD and integrated macular pigment. In four subjects who consumed lutein supplements, increases in MPOD corresponded to increases in photophobia light thresholds. Light absorption by macular pigment appears to influence the amount of short-wavelength light necessary to elicit photophobia.

Macular pigment optical density at four retinal loci during 120 days of lutein supplementation

Background:  Increased consumption of lutein and zeaxanthin has been shown to increase macular pigment optical density (MPOD) in some individuals. Most interventions either obtained infrequent measures of MPOD or measured MPOD at a single retinal locus.

Spectral responsivity of the white–black channel

Three subjects viewed, foveally and monocularly, a monochromatic test field of 0.6-deg diameter that was surrounded by a white annulus of 0.6-deg inner diameter and 4.5-deg outer diameter. The wavelength of the central test field was varied in steps of 10 nm from 440 to 640 nm, and its luminance was set to 100 Td. Center and surround were flashed together for 2 sec every 4 sec. The subjects adjusted the luminance of the surround so that the central field was perceived as having equal amounts of whiteness and blackness. The luminance of the surround required for this balance point varied with the wavelength of the test field in a manner that closely resembled a heterochromatic brightness matching function obtained under similar conditions. Control experiments ruled out the possibility that the subjects were making brightness matches between center and surround fields. Additional evidence was provided suggesting that the spectral responsivity of the putative white-black channel is best represented by a photopic spectral sensitivity curve based on equal brightness.

The elemental hues of short-wave and extraspectral lights

The continuous judgmental color-naming technique was used to assess the elemental nature of hue names descriptive of short-wave and extraspectral lights. Subjects were instructed to describe the hue of a 3-deg, 1-sec, 1,000-Td light by assigning percentages to each of three or four response categories available for use in a particular session. Response categories were chosen from the following group: red, green, blue, yellow, violet, and purple. Test stimuli consisted of monochromatic lights ranging from 510 to 420 nm and various proportions of 400-and 700-nm light. Results from eight subjects showed the color names blue, red, and green to be necessary and sufficient in describing these lights. On the basis of criteria established for the elementalness of hues, blue, red, and green were determined to be elemental, whereas purple and violet were found not to be elemental.

The prediction of hue and saturation for non-spectral lights

The Jameson and Hurvich opponent-colors model of hue and saturation was tested for spectral and non-spectral lights. Four observers described the color of lights by scaling hue and saturation. The lights ranged from 440 to 640 nm and consisted of five purities: 1.0, 0.80, 0.60, 0.40 and 0.20. Admixtures of monochromatic and a xenon-white light yielded the different colorimetric purities. For each subject, chromatic response functions were measured by the method of hue cancellation at each purity, and an achromatic response function was measured by the method of heterochromatic flicker photometry for spectral lights. Chromatic response functions measured for a particular purity and the achromatic response function were used to predict hue and saturation for that purity. The model successfully predicted hue at each level of purity, but failed to predict precisely the Abney effect. The model made relatively poor predictions of saturation, tending to overestimate short-wave lights and underestimate long-wave lights. An additional experiment found that stimulus parameters that favor rod contribution weaken the models predictions of saturation, while stimulus parameters that do not favor rod contribution improve the models predictions of saturation.

Colors of monochromatic lights that vary in contrast-induced brightness

Using a color-naming procedure, two subjects described monochromatic lights, ranging from 450 to 630 nm, that were surrounded by perceptually unique-white fields of variable retinal illuminance. The test fields were 0.6 deg and 10, 100, or 1,000 Td. The surrounds, which were 4.5 deg in outer diameter, ranged from 0 to approximately 31,000 Td. From the resulting color-naming functions, equal-hue contours were derived, with surround intensity plotted against wavelength, for the spectral unique hues and the binary hues blue-green, green-yellow, and yellow-red. The wavelengths for unique blue, unique yellow, and blue-green were essentially invariant with changes in surround intensity. The spectral locus for unique green was also invariant at higher test-field intensities, but, at lower levels, it generally shifted toward shorter wavelengths as surround intensity increased. Nonmonotonic shifts were found for green-yellow and yellow-red. The contrast and the wavelength requirements for the color brown were nearly invariant with the changes of test-field intensity. Over the full range of surround intensities, subjects described the test fields as consisting of one or two hues plus white or black, depending on the surround level, but never (except for one subject at the lowest test-field intensity) white and black simultaneously and cospatially. This opponent aspect of black and white was compared with that associated with the chromatically opponent processes.

The contribution of chromatic and achromatic valence to spectral saturation.

The spectral efficiency of the achromatic and opponent chromatic channels was measured in three subjects by use of heterochromatic flicker photometry and hue cancellation, respectively. Heterochromatic brightness matching was also used for measuring achromatic spectral efficiency. These data were then used to predict spectral saturation based on Hurvich and Jamesons (1957; Psychological Review, 64, 384-404) opponent colors model. A standard color-naming procedure and a saturation matching technique were used for measures of spectral saturation. The ratio of saturation of short-wave to long-wave lights was found to be less than that predicted by the linear valence model. Allowing for nonlinearity at the opponent site of the yellow-blue channel plus a desaturating signal from the rods provided a good fit between data and theory.

A simple but powerful theory of the moon illusion

Modification of Restles theory (1970) explains the moon illusion and related phenomena on the basis of three principles: (1) The apparent sizes of objects are their perceived visual angles. (2) The apparent size of the moon is determined by the ratio of the angular extent of the moon relative to the extents subtended by objects composing the surrounding context, such as the sky and things on the ground. (3) The visual extents subtended by common objects of a constant physical size decrease systematically with increasing distance from the observer. Further development of this theory requires specification of both the components of the surrounding context and their relative importance in determining the apparent size and distance of the moon.

Black spectral responsivity.

Six subjects induced blackness within a circular broadband field by increasing the radiance of a surrounding monochromomatic annulus, which varied in wavelength. Between the central field and the annulus was a thin dark ring. Half of the subjects were instructed to increase the radiance of the annulus until the central field just turned black, and the other half were instructed to increase the radiance of the annulus until the contour between the central field and the dark ring disappeared. Spectral luminous efficiency functions measured by the methods of heterochromatic flicker photometry (HFP) and brightness matching (HBM) were determined for each subject and compared with the subjects blackness-induction functions. The hypothesis that the contour-disappearance instruction would yield blackness-induction curves best fitted by flicker photometric functions and that the absolute-blackness instruction would yield blackness-induction curves best fitted by HBM functions was not confirmed. There was only one subject for whom the spectral efficiency of blackness was represented better by HFP than by HBM. There was one subject for whom blackness spectral efficiency was fitted better by HBM than by HFP. For the remaining four subjects, there was no difference in fits.