ACTION OF COLOUR FLICKER STIMULI ON THE ELECTRICAL RESPONSES OF RETINA AND OPTIC CORTEX IN MAN.
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Adaptation, Ocular↗
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[The analysis of refractive error in children and adolescents from 6-15 years of age based on 1000 examinations in two major Polish regions].
PURPOSE: The aim of this study is to present the results of screening examinations of refractive errors, taken on 1002 of school children ranging from 6 to 15 years of age. MATERIAL AND METHODS: As the result of Internet screening visual acuity and color perception tests named "I can see..." in 10,021 children from randomly chosen schools in Poland in the year 2002, the group of 1002 children was chosen. In this group, the subjective and objective refractive error examination was taken as well as the visual acuity test, color perception with the use of Ishihara tables and full ophthalmologic examination. RESULTS: Average visual acuity was RE: 0.72 (SD +/- 0.31) and LE: 0.72 (SD +/- 0.31). The prevalence of emmetropia was 34%. In the examined group myopia in 17%, hyperopia in 20%, astigmatism in 5.5% of children was found, and in 24.5% of patients complex errors occur such as myopic and hyperopic astigmatism.
Adolescent↗
[Dyschromatopsias and pictorial art].
The influence of color vision defects on pictorial art was studied using three methods. 1) From a theoretical standpoint, the possibilities of choice of the color-blind painter are determined by the nature of his color perception. Characteristic errors result from the fact that he has to choose between many hues which are different to a normal individual but which all look the same to him. 2) Evaluation of the clinical cases of painters with dyschromatopsias has shown evidence of the following: a) the color-blind painter makes mistakes according to the type of color defect; b) if the color-blind painter makes several copies of the same model, he makes different mistakes at each attempt; c) when several color-blind painters make copies of the same model, they also make different mistakes, even when they suffer from the same type of color vision defect. Preferences for some colored patterns were studied by means of a forced choice procedure and choices of color-blind individuals were often characteristic of their dyschromatopsia. Recent clinical case of acquired dyschromatopsia reported in the literature are discussed, as is a personal case of a painter suffering from tapeto-retinal degeneration. This was a severe dyschromatopsia with a neutral zone in purple (so-called scotpic axis, by Verriest's terminology). The painting of this artist tended to be monochromatic, mainly in green and green-blue colors. 3) Recent studies in art history have shown that only the romantic etcher Meryon was definitively color deficient. The more dubious cases of the Polish painter Grottger and of Eugène Carrière are discussed and conclusions are negative. Among acquired dyschromatopsias, there have been many recent papers devoted to cataract dyschromatopsias, concerning the cases of Rouault, Monet and Mary Cassatt. The hypothesis of a degree of chromatopsia or dyschromatopsia of toxic origin in the case of Van Gogh is also assessed. In conclusion, the problem of the relations between congenital or acquired dyschromatopsias and pictorial art seems very complex and great care is required when making deductions and advancing hypotheses.
Color Perception↗
Color "amnesia" without aphasia.
Following an apparent left parietal CVA, a patient developed a severe and nearly complete color amnesia which was not associated with any disturbance in color vision or color perception. Like all previously reported cases with color amnesia, this patient was alexic but, unlike most previously reported cases, he was not aphasic.
Agnosia↗
Cues and strategies for color constancy: perceptual scission, image junctions and transformational color matching.
The identification of objects, illuminants, and transparencies are probably the most important perceptual functions of color. This paper examines the effects of perceptual scission, image junctions, color adaptation, and color correlations on identification. Simulations of natural illuminants, materials, and filters were used in a forced-choice procedure to simultaneously measure thresholds for identifying filters and objects across illuminants, and discrimination thresholds within illuminants. In the vast majority of the cases, if observers could discriminate within illuminants they could identify across illuminants. Since results were similar for identical color distributions, whether transparency cues like X-junctions were present or not, the primary cues for color identification were systematic color shifts across illuminants. These color shifts can be well described by three-parameter affine transformations, and the parameters can be derived from differences and ratios of mean chromaticities. A strategy based on post-transformation color matching predicts generally accurate identification despite perceptible color shifts, and also provides plausible reasons for those few conditions where identification thresholds are significantly higher than discrimination thresholds.
Color Perception↗
The primacy of chromatic edge processing in normal and cerebrally achromatopsic subjects.
The local chromatic contrast between surfaces in a visual scene plays an important role in theories of color perception. Our studies of cerebral achromatopsia suggest that this contrast signal is computed independently of the more complex processes such as edge integration and anchoring. We report a study in which we attempted to determine whether local-contrast signals also drove behavior in normal subjects. We sought to reduce the role of edge integration and anchoring by using stimuli whose background varied very gradually in color from top to bottom. The local chromatic contrast of patches relative to such backgrounds depends upon the position at which they are presented. It is therefore possible for patches with identical spectral composition to have opposite contrasts. We constructed stimuli in which two of three vertically arranged discs had the same contrast while the third had opposite contrast. The stimuli were also constructed so that the contrast-odd disc and one of the other two had identical spectral composition while the third disc had different composition. We used these stimuli in an attentional task where, after a brief delay, a letter discrimination target was presented in the location of one of the discs. Attention should automatically be attracted to the odd disc in such a display. Normal observers were faster at making the letter discrimination when the target appeared at the contrast-odd as opposed to spectrally odd location. We conclude that local chromatic contrast, but not raw spectral composition, is accessible to normal observers at an appropriate stage in visual processing to drive attention.
Adult↗
[Retinal function under conditions of artificial illumination with varying spectral makeup in patients with sclerotic macular dystrophy].
In conditions of a laboratory experiment using illumination of various light sources (by incandescent, luminescent, arc-mercury, natrium lamps), determination of visual acuity, visual field, color perception, restoration time of visual acuity after macular flash lighting (photostress test), Heidinger's phenomenon as well as visocontrastometry after V. V. Volkov, Weston's correction test were conducted in 46 patients (92 eyes) with macular dystrophy and 50 healthy persons in the dynamics of a working day. It was found that the spectral composition of the visible light has a remarkable influence on the function of color perception, contrast sensitivity, reaction of visual analyser on light load, visual ability to work. In patients with macular dystrophy, the dependence on the light medium was expressed much greater than in healthy persons. The highest functional state of the retina and visual ability to work in patients with macular dystrophy were provided by natrium lamps having a maximum radiation in the yellow part of the spectrum. The short-wave visible light of arc-mercury and luminescent lamps somewhat suppressed the functional state of the retina and reduced visual ability to work. The results obtained are important for selection of optimal conditions of work for patients with macular dystrophy.
Adult↗
Illuminant estimation as cue combination.
This work briefly describes a model for illuminant estimation based on combination of candidate illuminant cues. Many of the research issues concerning cue combination in depth and shape perception translate well to the study of surface color perception. I describe and illustrate a particular experimental approach (perturbation analysis) employed in the study of depth and shape that is useful in determining whether hypothetical illuminant cues are actually used in color vision.
Color Perception↗
Red-green chromatic mechanisms in normal aging and glaucomatous observers.
PURPOSE: This study was designed to determine whether normal aging and glaucoma are associated with red-green (R/G) chromatic processing abnormalities, a function that is primarily performed by the parvocellular visual pathway. METHODS: Chromatic processing mechanisms were examined in 98 glaucomatous observers (between the ages of 49 and 93 years; mean age, 70.8 +/- 9.4 [SD]) and 67 normal observers (between the ages of 49 and 88; mean age, 70.6 +/- 10.6 years) with the use of the minimum-motion and motion-nulling paradigms. Phakic glaucomatous (n = 60; mean age, 68.7 +/- 8.9 years) and normal (n = 32; mean age, 69.8 +/- 10.6 years) and pseudophakic glaucomatous (n = 38; mean age, 74 +/- 9.4 years) and normal (n = 35; mean age, 71.4 +/- 10.6 years) subjects were tested to evaluate the effects of lenticular aging on color perception. RESULTS: Phakic observers (normal or glaucomatous) displayed significantly different minimum-motion values than did both their younger counterparts and all the pseudophakic subjects. These results suggest that normal aging with the presence of a natural lens is accompanied by a significant decrease in green-light sensitivity, an effect that is not exacerbated by glaucoma and is primarily related to optical factors. The data also revealed no differences in color motion perception between groups, indicating that the higher cortical mechanisms of the parvocellular pathway implicated in the analysis of information about the middle and long wavelengths of the visible spectrum are not selectively affected by the disease process and normal aging. CONCLUSIONS: Normal aging and glaucoma do not produce significant R/G chromatic processing deficits at retinal and postretinal levels when optical factors are excluded. The authors propose the hypothesis that glaucoma-related effects on motion perception and blue-on-yellow perimetry should be viewed as evidence of loss of ganglion cells that necessitates integration of information over larger retinal areas and more receptor cells than in the R/G chromatic system. Ganglion cells with large receptive fields involve more neural connections and are less numerous than those that respond to R/G information. The functional consequence of this could be that the loss of a single ganglion cell with a larger receptive field would have a greater impact on visual function than the loss of a ganglion cell with a smaller receptive field, such as the ones that process R/G information. The authors believe that glaucoma-induced functional loss is best viewed as related to receptive field structure and function rather than to anatomic cell-type damage.
Aged↗
Perceptions of color preferences-a clue to marital prediction?
In a study of marital adjustment prediction (N = 75 couples), each spouse was asked to indicate a color preference for nine common household articles and predict which color the spouse would choose. A discrepancy score between perceived and actual choices was calculated and compared with scores on the Nye-MacDougall Martial Adjustment Scale. The correlation coefficient between the discrepancy score and ego's marital adjustment was -.27 for the sample as a whole, -.33 for husbands, and -.21 for wives. The correlation between the discrepancy score and mate's marital adjustment was -.17 for the whole sample, -.10 for husbands, and -.23 for wives.
Adaptation, Psychological↗
[The influence of lighting upon the subjective perception of color in the choice of shades for aesthetically adequate crowns and facets].
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Acrylic Resins↗
[The phenotype of heterozygotic females in congenital red-green color blindness (author's transl)].
Varying degrees of deficient color perception along the Deutan axis within one family have been studied and presented. All seven family members exhibit manifest color blindness. The question of the phenotype among heterozygotic females is discussed on the basis of the data found by anomaloscope testing and the hue tests of Farnsworth D-15 and Farnsworth 100.
Color Perception Tests↗
Regeneration of specific nerve cells in lesioned visual cortex of the human brain: an indirect evidence after constant stimulation with different spots of light.
The defective parts of the visual field of two brain-injured patients were stimulated with different spots of light. There is evidence for at least five independent visual functions which can be restored due to constant stimulation of the blind part of the visual field: (1) The constant stimulation of the blind part of the visual field with spots of white light leads to an increase of the visual field for the perception of white light only. (2) The constant stimulation with spots of light of different wavelengths leads to an increase of the visual field for different color perception. To enlarge the visual field for the perception of the color red, a light stimulus with the wavelength of 656 nanometers (nm) was used; for the visual field for the perception of the color green 525 nm; for yellow 578 nm; and for blue 450 nm. (3) The constant stimulation of the blind visual field with black and white light bars of different orientations and constellations leads to an increase of the foveal acuity and an improvement of form perception in the periphery of the visual field. The results suggest that the recovery of visual functions, different color perception and form perception, may depend upon neuronal regeneration in the human visual cortex; regeneration occurs with adequate and constant stimulation of its specific neurons.
Adolescent↗
Acute blindness and putaminal necrosis in methanol intoxication.
PURPOSE: To review the neuro-ophthalmological and radiological findings of acute methyl alcohol intoxication. METHOD: 8 acute methyl alcohol intoxication cases were evaluated. RESULTS: All patients were male and their ages varied between 21 and 55. At the initial examination, 6 to 12 days after methanol intake, visual acuity ranged from no light perception to counting fingers at 2 meters with no color perception. Bilateral dense central scotomas were detected in patients whose vision was slightly preserved. Pupillary light reactions were either absent or sluggish. In 4 cases, edema of the optic disk and the peripapillary nerve fiber layer was observed. Three months later, optic atrophy had developed. Five patients underwent magnetic resonance imaging. Bilateral putaminal hyperintense lesions on T2 weighted images were observed in 3 cases. Two patients died and autopsy permission could not be obtained. Follow-up examination 12 months later revealed optic atrophy in the other six cases, with no improvement in vision. CONCLUSION: Methanol intoxication is detrimental to health, possibly resulting in blindness and occasionally death. In association with ocular signs and the other systemic and laboratory features, the ophthalmologist should be alert to the diagnosis of methanol intoxication in which visual loss may be the only symptom.
Acute Disease↗
[Current problems of ophthalmologic examination in automobile drivers].
The article deals with major aspects of eye examination in automobile drivers, with main drawbacks of occupational selection, absence of efficient diagnostic devices, with various approaches to inspection of color perception.
Automobile Driving↗
Color discrimination, color naming and color preferences in 80-year olds.
The aim of the present study was to investigate color discrimination, color naming and color preference in a random sample of 80-year-old men and women. Knowledge of color perception in old age can be of value when using color contrast, cues and codes in the environment to promote orientation and function. The color naming test indicated that the colors white, black, yellow, red, blue and green promoted recognition to the highest degree among all subjects. A gender-related difference, in favor of women, occurred in naming five of the mixed colors. Women also used more varied color names than men. Color discrimination was easier in the red and yellow area than in the blue and green area. This result correlates positively with visual function on far sight, and negatively with diagnosis of a cataract. The preference order for seven colors put blue, green and red at the top, and brown at the bottom, hence agreeing with earlier studies, and indicating that the preference order for colors remains relatively stable also in old age. This result should be considered when designing environments for old people.
Aged↗
Selective color constancy deficits after circumscribed unilateral brain lesions.
The color of an object, when part of a complex scene, is determined not only by its spectral reflectance but also by the colors of all other objects in the scene (von Helmholtz, 1886; Ives, 1912; Land, 1959). By taking global color information into account, the visual system is able to maintain constancy of the color appearance of the object, despite large variations in the light incident on the retina arising from changes in the spectral content of the illuminating light (Hurlbert, 1998; Maloney, 1999). The neural basis of this color constancy is, however, poorly understood. Although there seems to be a prominent role for retinal, cone-specific adaptation mechanisms (von Kries, 1902; Pöppel, 1986; Foster and Nascimento, 1994), the contribution of cortical mechanisms to color constancy is still unclear (Land et al., 1983; D'Zmura and Lennie, 1986). We examined the color perception of 27 patients with defined unilateral lesions mainly located in the parieto-temporo-occipital and fronto-parieto-temporal cortex. With a battery of clinical and specially designed color vision tests we tried to detect and differentiate between possible deficits in central color processing. Our results show that color constancy can be selectively impaired after circumscribed unilateral lesions in parieto-temporal cortex of the left or right hemisphere. Five of 27 patients exhibited significant deficits in a color constancy task, but all of the 5 performed well in color discrimination or higher-level visual tasks, such as the association of colors with familiar objects. These results indicate that the computations underlying color constancy are mediated by specialized cortical circuitry, which is independent of the neural substrate for color discrimination and for assigning colors to objects.
Adaptation, Physiological↗
Observer perception of skin color in a study of malignant melanoma.
Observer perceptions of skin color with a 15-step skin tone panel were evaluated during an as yet unpublished case-control study of malignant melanoma. Skin color is a risk factor for melanoma, and the skin tone panel was introduced in an effort to reduce its misclassification. Reflectances of the 15 artificial skin tones were measured at four wavelengths with a reflectance spectrophotometer. Six observers each evaluated the skin color of eight study subjects twice under three lighting conditions, and the results were transformed to reflectance values. Components of variance analysis demonstrated that between-subject variability contributed 63% or more of the variance at wave-lengths of 400-600 nm, while observers, light source, observation time, and error contributed 30% or less. At 700 nm, only 25.5% of the variance was due to subjects, indicating lower levels of reliability. Similarly, the correlation of visual and spectrophotometric assessment of skin reflectance was higher at 400-600 nm (r = 0.63-0.71) than at 700 nm (r = 0.41). Thus, the value of the skin tone panel-based assessments depends upon knowledge of which wavelengths most closely relate to the physiologic risk factor. For instance, reflectance at 650-700 nm is a better measure of skin melanin content than reflectance at lower wavelengths. Since the role of melanin as a risk factor remains in doubt, the utility of this technique has yet to be demonstrated. However, data from the case-control study and from this validity and reliability study will allow us to develop an analytic approach that minimizes misclassification of skin color as a confounder.
Analysis of Variance↗