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PubMed1997

Influence of boundary information on the perception of color.

The integration of color and form to produce a unified percept is a central problem in vision research. We know that the spatial arrangement of colored stimuli influences their detectability. In the gap effect, for example, a small gap between two colored fields enhances their discriminability [Opt. Acta 24, 159 (1977)]. Chromatic thresholds are also reduced when test fields are spatially demarcated. To explore the mechanisms underlying these types of effect, the influence of spatial structure on chromatic sensitivity for gratings was measured. For sine-wave and square-wave gratings modulated in different directions in color space, contrast sensitivity was measured by using a two-alternative forced-choice procedure with a QUEST staircase. Thin lines, of the same orientation as that of the grating, were superimposed on it at half-cycle intervals. The phase of the superimposed lines was varied. For S-cone modulated gratings, dark lines placed at the midpoints between peaks and troughs (90 degrees) increased sensitivity. As the phase of the lines moved toward the peaks (0 degree), their effect on sensitivity declined to zero. A similar but smaller effect was seen for isoluminant L- and M-cone modulated gratings. The superimposed lines always impaired contrast sensitivity for achromatic gratings, especially at a phase of 0 degree. Spatial structure superimposed on gratings can both facilitate and impair contrast sensitivity. In the presence of sharp boundaries, chromatic sensitivity is increased. This effect may depend more on the salience of boundaries, since isoluminant lines superimposed on S-cone modulated gratings and gray lines of similar cone contrast can facilitate detection if they are of sufficient contrast. Achromatic contrast sensitivity is reduced when the boundaries are present. The additional luminance information at the boundaries masks the grating. A simple model in which spatial integration is arrested at the positions of the superimposed lines fits only the isoluminant conditions. For both luminance and chromatic contrast the change in sensitivity depends on phase.

Color Perception↗
PubMed1985

A central spectrum model for the perception of coloration in filtered Gaussian noise.

In this paper we describe a monaural auditory signal-processing model for the perception of coloration. The model gives a central spectrum display of a stationary input signal. The central spectrum level for a nerve fiber tuned to a given frequency is computed as a combination of the average firing rate and the firing synchronized to the center frequency of the nerve. The model incorporates a critical-band filter bank, steady-state representations of the average and synchronized firing rates, and temporal integration. The central spectrum model, when used to process simulated data, accurately predicts the perception of coloration in filtered Gaussian noise.

Auditory Perception↗
PubMed1998

Reversible color vision loss in occupational exposure to metallic mercury.

Color vision was evaluated in twenty-one mercury exposed workers and referents matched for sex, age, tobacco smoking, and alcohol habits. The Lanthony 15 Hue desaturated panel (D-15 d) was applied. In the workers, mean urinary Hg (HgU) was 115+/-61.5 microg/g creatinine; in all but one the values exceeded the biological limit (BEI) proposed by the American Conference of Governmental Industrial Hygienists. A dose-related subclinical color vision impairment was observed in Hg-exposed workers compared to the referents. Just after the survey, working conditions were improved. Twelve months later the workers were reexamined. Mean HgU was 10.0 microg/g creatinine and in no subjects was the BEI exceeded. Color perception was significantly improved compared to the first examination and, furthermore, no differences were observed between exposed workers and referents. The results add evidence that the color vision loss observed during the first part of the study was related to Hg exposure and, moreover, show that this effect is reversible. These data indicate that metallic Hg can induce a reversible impairment in color perception. This suggests that color vision testing should be included in studies on the early effects of Hg. The possibility of applying the D-15 d as an early effect index in the biological monitoring of Hg exposed workers should also be entertained.

Adult↗
PubMed1984

The effect of glaucoma on central visual function.

Glaucoma has traditionally been thought to affect peripheral visual function in its early stages and to spare central visual function until late in the disease process. The basis for this assumption has been the reliance on Goldmann-type perimetry, a rather sensitive method for assessing the peripheral visual function, and on Snellen-type visual acuity measurements, a rather insensitive method of assessing central visual function. This belief has persisted despite frequent complaints from patients with glaucoma that their central vision is disturbed. Over the past two decades, several investigations of central visual functions and their anatomic substrate have challenged this assumption. Histologic studies of the nerve fiber layer in eyes with glaucoma suggest that the number of ganglion cells subserving macular function is decreased even in early stages of the disease. In addition, afferent pupillary defects (a gross measurement of macular nerve fiber function) may also be present in eyes with early glaucoma. Several studies have demonstrated that color perception (largely mediated by the fovea) is defective in glaucoma. Furthermore, defects in color perception may even precede the development of visual field abnormalities. Seventy-eight percent of patients with early glaucomatous visual field defects were found to have a defect in color perception when tested with a desaturated D-15 color panel that tests only the central 1.5 degrees. In addition, both chromatic and achromatic foveal perception channels are defective in eyes with glaucoma and even in some eyes of those with suspected glaucoma. Contrast sensitivity has become recognized as an important component of visual function. Partial loss of contrast sensitivity may cause a degradation in the quality of perception even though the Snellen visual acuity remains normal. Although contrast sensitivity is not entirely a macular function, it has been shown that as little as 3 degrees of disturbance of the macula (eg, with macular degeneration or with an artificial central scotoma) will reduce the contrast sensitivity, suggesting that this modality is indeed mediated to a significant extent by this portion of the retina. Spatial contrast sensitivity appears to be reduced in patients with glaucoma. However, because of overlap and lack of a sharp cutoff measurement, present testing procedures fail to allow a clear distinction between the glaucomatous and normal populations. Although reduced temporal contrast sensitivity has been demonstrated in glaucomatous eyes by others, I undertook a systematic investigation of this function in a large group of patients with glaucoma and with suspected glaucoma.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMedDate not supplied

A model of color vision based on cortical reentry.

It is known that the perceived color of an object depends on the context in which it is viewed, its reflectance properties and the spectral distribution of the illuminating light. What is not known, however, is how the visual system functions so that color percepts depend upon the integration of local and contextual cues. While phenomenological theories of color vision exist, robust neurally based theories consistent with psychophysical observations are sparse. In the present study we develop such a theory and establish its self-consistency by computer simulations of cerebral cortical areas involved in color perception. The simulations test the hypothesis that long-range reciprocal connections within and between cortical areas mediate a dynamic process of reentry that integrates contextual cues into the color percept. When stimuli similar to those used in psychophysical testing of contextual influence were used, firing patterns consistent with psychophysical data on color constancy and color induction in humans were observed. Selective disruption of reciprocal inter- or intra-areal connections reduced the correspondence between the model's responses and the psychophysical data. The findings are consistent with the proposal that reentrant interactions within and between cortical areas provide a major basis for the context-sensitive aspects of color vision.

Animals↗
PubMed1990

[The study of color vision in children].

The paper analyses results after investigation of color perception in 520 children (264 boys and 256 girls), aged 3-5 years, by means of two simple tests: a "Pflüger-Trident Test" (Velhagen) and a "Simplified Test of Color Vision" (Fletcher). It is proved that in children of under school age color perception is already developed enough and can be investigated for detecting disturbances in color vision.

Child, Preschool↗
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↗
PubMedDate not supplied

[Color vision in diabetics].

Color perception is often already altered even if the ocular, anatomic and functional exams maintain their results within the normal limits. This fact is more important in diabetes, where chromatic abnormalities exist at half of the subjects, even if they do not reveal any signs of diabetic retinopathy. The authors present some of the methods in clinical exam of color perception, the characters of dyschromatopsia and glycemic self control using the method of coloured bandelets, types of dyschromatopsia which may appear during the evolution of the diabetes, and also the predictive effect of dyschromatopsia for the appearance of diabetic retinopathy.

Color Perception↗
PubMed1998

Discoloration of a compomer by stains.

This study evaluated the color stability of a polyacid-modified composite (compomer) upon exposure to stains. Five disks were prepared for immersion in each of five stains: coffee, chlorhexidine, cola, red wine, and water as a control. Color measurements were made on a reflection spectrophotometer at baseline, after 24-hour incubation, and after 24, 48, and 72 hour immersion in each stain. At 24 hours, perceptible color changes occurred for specimens in red wine and coffee. After 48 hours, perceptible color changes occurred for specimens in cola. Chlorhexidine and water caused no perceptible color changes. A compomer is susceptible to staining by coffee, red wine, and cola.

Analysis of Variance↗
PubMed1992

Absence of smooth motion perception in color vision.

We have tested the behavioral evidence for a separation of the processing of color contrast from motion in the human visual system. Two different aspects of motion perception are examined; the identification of the direction of movement of a chromatic grating and the perception of smooth motion. The results show that color vision is at no great disadvantage in the identification of direction of movement, since this can be done at color contrasts quite close to detection threshold over a wide range of spatial and temporal frequencies. However, we find that subjects can identify direction without having the genuine perception of smooth motion. Smooth motion perception is revealed to be highly impaired since it is detected only at very high color contrasts and over a narrow range of spatial temporal conditions.

Color Perception↗
PubMed1996

Preserved color imagery in an achromatopsic.

The loss of color vision secondary to central nervous system disease (achromatopsia) is thought to preclude visual imagery of colors. We report a patient with achromatopsia, secondary to bilateral temporo-occipital infarcts inclusive of the lingual and fusiform gyri, with preserved color imagery. Our findings, in conjunction with previous cases in the literature, are consistent with a single neural network for color processing in which a disconnection of internal activation from stored color representations produces impaired color imagery with preserved color perception, whereas a disconnection of visual input to these representations produces achromatopsia with preserved color imagery.

Cerebral Infarction↗
PubMed1998

[Standardized evaluation of red, green and blue perception. Comparison between color arrangement and computer-assisted test procedures].

BACKGROUND: Computerized colortests offer the possibility of determining quantitative color contrast thresholds under standardized conditions. Arrangement tests allow semi-quantitative evaluation of the red, green and blue color sense. To validate the results of a new computerized test, its results are compared to those of arrangement tests. PATIENTS AND METHODS: Thirty-five patients with retinitis pigmentosa (RP, mean age 38.51, +/- 15.14) as well as 30 normal observers (mean age 36.52, +/- 14.33) were evaluated. The computerized color test COLDEF was used, which is a calibrated screen that presents color optotypes on a colored background. All colors are chosen from three-color confusion axes of the CIE-Lu'v' color chart (protan, deutan and tritan axis). By a staircase procedure, the colors of the optotype and background were varied until the observers minimal color contrast threshold is detected. To compare the results of COLDEF with a routine diagnostic tool, the Farnsworth panel D-15 and Lanthony désaturé test were chosen. The results of the arrangement tests were scored by a categorization scheme. RESULTS: Normal observers showed no elevated thresholds either in COLDEF nor in the panel tests. In the RP group increased thresholds along the blue confusion axis could be detected in most cases. Furthermore, COLDEF showed increased thresholds along the red and green axes in some patients. With the computerized test it is always possible to identify the color axis concerned. The new test allows a fast and quantitative assessment of acquired color vision deficiencies.

Adult↗
PubMed1989

Molecular patterns of X chromosome-linked color vision genes among 134 men of European ancestry.

We used Southern blot hybridization to study X chromosome-linked color vision genes encoding the apoproteins of red and green visual pigments in 134 unselected Caucasian men. One hundred and thirteen individuals (84.3%) had a normal arrangement of their color vision pigment genes. All had one red pigment gene; the number of green pigment genes ranged from one to five with a mode of two. The frequency of molecular genotypes indicative of normal color vision (84.3%) was significantly lower than had been observed in previous studies of color vision phenotypes. Color vision defects can be due to deletions of red or green pigment genes or due to formation of hybrid genes comprising portions of both red and green pigment genes [Nathans, J., Piantanida, T.P., Eddy, R.L., Shows, T.B., Jr., & Hogness, D.S. (1986) Science 232, 203-210]. Characteristic anomalous patterns were seen in 15 (11.2%) individuals: 7 (5.2%) had patterns characteristic of deuteranomaly (mild defect in green color perception), 2 (1.5%) had patterns characteristic of deuteranopia (severe defect in green color perception), and 6 (4.5%) had protan patterns (the red perception defects protanomaly and protanopia cannot be differentiated by current molecular methods). Previously undescribed hybrid gene patterns consisting of both green and red pigment gene fragments in addition to normal red and green genes were observed in another 6 individuals (4.5%). Only 2 of these patterns were considered as deuteranomalous. Thus, DNA testing detected anomalous color vision pigment genes at a higher frequency than expected from phenotypic color vision tests. Some color vision gene arrays associated with hybrid genes are likely to mediate normal color vision.

Color Perception↗
PubMed1997

Accelerated aging affects color stability of provisional restorative materials.

PURPOSE: The color stability of two shades each of five acrylic resin and seven resin composite provisional restorative materials was evaluated by reflection spectrophotometry following in vitro accelerated aging. MATERIALS AND METHODS: Specimens of provisional restorative materials were polymerized according to manufacturers' instructions and aged in an artificial aging chamber with exposure to a total ultraviolet irradiation of 60 kJ/m2. Color was measured by CIE L*a*b* on a reflection spectrophotometer before and after aging. Color change (delta E*) was calculated and analyzed statistically. RESULTS: Statistically significant changes in color were observed after accelerated aging. Nine of the 12 provisional materials tested showed perceptible color change of at least one of the shades tested. The most color-stable materials were the acrylic, Alike, and the resin composites, Luxatemp and Protemp Garant, which had no perceptible color changes under these conditions. CONCLUSIONS: Some acrylic resin and composite provisional materials change color significantly and perceptibly when exposed to in vitro accelerated aging conditions.

Acrylic Resins↗
PubMed1995

Testing color discrimination without the use of special stimuli or technical equipment.

Recently a number of self-report inventories have been developed to provide quick, valid, and reliable measures of sensory function without the use of technical equipment. One such measure, the 10-item Color Screening Inventory, was developed to detect individuals with deficient color perception. In the present study we used a sample of 268 subjects who were tested on both the Farnsworth-Munsell 100-hue test and the Color Screening Inventory. Analysis showed that inventory scores also predict continuous variations in and individuals' ability to discriminate colors, with an eta of .69, which explains 48% of the predictive variance. It was possible to describe the data using a quadratic regression equation which has a corrected correlation of .52. Using this, a conversion table was generated to allow rapid estimation of 100-hue test scores from the inventory. On the basis of the results, the Color Screening Inventory appears to be a quick and effective means of testing color discrimination without requiring special stimuli, technical equipment, or controlled testing environments.

Adult↗