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Biomedical subjects

K Fuld

Publications and source records attributed to K Fuld.

9 recordsLinked to original sources
PubMed1992

Interocular differences in macular pigment density.

Interocular differences in the optical density of macular pigment were examined. Foveal and parafoveal sensitivities to lights of 460 and 530 nm were measured by heterochromatic flicker photometry for both eyes of ten subjects. These two wavelengths represent the maximum and minimum absorbance for macular pigment. Taking the difference in log sensitivity to the 460 nm light for the fovea and parafovea, after normalizing with respect to 530 nm, yields a measurement of the optical density of the macular pigment. Consistent interocular differences in macular pigment density were found for only two subjects, and these differences were less than 0.1. Other subjects frequently showed significant interocular differences on a given day but showed no consistent differences over the course of many days. In general, the amount of macular pigment measured for one eye was found to be essentially the same as that for the other eye. When measurements were averaged for the two eyes of each subject, significant differences in macular pigment density among subjects were found.

Adult↗
PubMed1991

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 Jameson's (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.

Adult↗
PubMed1990

A simple but powerful theory of the moon illusion.

Modification of Restle's 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.

Distance Perception↗
PubMed1989

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 subject's 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.

Color Perception↗
PubMed1975

Photopic spectral sensitivity of the peripheral retina.

Photopic spectral sensitivity was determined in the mid- and far-peripheral retina by two methods. The first consisted of measuring increment thresholds on a background similar in spectral composition to CIE Source A. The resulting spectral-sensitivity functions displayed maxima at about 440 nm, in agreement with previous work. The second method consisted of measuring dark-adaptation curves following termination of the background. From these curves, spectral-sensitivity functions were derived for various times in the dark. The results showed that the 440 nm maximum quickly diminished. When photopic thresholds were estimated from the cone plateau of the dark-adaptation curves, the spectral-sensitivity functions peaked at about 550 nm and had much the same shape from the parafovea to the far periphery. We suggest that previous findings of maximum photopic sensitivity in the short-wave region of the spectrum resulted from chromatic adaptation induced by backgrounds (such as Source A) that were weighted towards middle and long waves.

Adult↗