Learning space perception with colors.
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Child↗
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Results for “Color Perception”
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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↗
[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↗
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↗
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↗
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↗
Escher in color space: individual-differences multidimensional scaling of color dissimilarities collected with a gestalt formation task.
The structure of color perception can be examined by collecting judgments about color dissimilarities. In the procedure used here, stimuli are presented three at a time on a computer monitor and the spontaneous grouping of most-similar stimuli into gestalts provides the dissimilarity comparisons. Analysis with multidimensional scaling allows such judgments to be pooled from a number of observers without obscuring the variations among them. The anomalous perceptions of color-deficient observers produce comparisons that are represented well by a geometric model of compressed individual color spaces, with different forms of deficiency distinguished by different directions of compression. The geometrical model is also capable of accommodating the normal spectrum of variation, so that there is greater variation in compression parameters between tests on normal subjects than in those between repeated tests on individual subjects. The method is sufficiently sensitive and the variations sufficiently large that they are not obscured by the use of a range of monitors, even under somewhat loosely controlled conditions.
Color Perception↗
A functional MRI case study of acquired cerebral dyschromatopsia.
Evidence from imaging studies suggests that primary visual cortex and multiple areas in ventral occipitotemporal cortex subserve color perception in humans. To learn more about the organization of these areas, we used structural and functional MRI (fMRI) to examine a patient with damage to ventral cortex. An art professor, KG, suffered a cerebrovascular accident during heart surgery that impaired his ability to perceive color. The Farnsworth-Munsell 100-Hue test was used to assess the extent of his deficit. When tested 12 months after the lesion, KG performed worse than 95% of age-matched normals on the 100-Hue test, but well above chance. Structural and functional MRI studies were conducted 3 years after the lesion to investigate the neuroanatomical correlates of KG'ss remaining color ability. Structural MRI revealed bilateral damage to ventral occipitotemporal cortex. In young and age-matched normal controls, an fMRI version of the 100-Hue reliably activated bilateral, color-selective regions in primary visual cortex and anterior and posterior ventral cortex. In subject KG, color-selective cortex was found in bilateral primary visual cortex. In ventral cortex, no color-selective activity was observed in right ventral cortex, and only a small area of activity was observed in left anterior ventral cortex. However, significant color-selective activity was observed in posterior left ventral cortex spared by the lesion. This posterior left ventral activation was similar in extent, position, and degree of color-selectivity to the posterior left posterior activation observed in normal controls, suggesting that this focus may be the cortical substrate underlying KG's remaining color perception.
Adult↗
Role of perceptual organization in chromatic induction.
Color matches between two small patches were made in a display containing ten larger regions of different chromaticities. The spatial organization of the ten regions was varied while keeping constant the immediate surround of each patch as well as the space-average chromaticity of the entire stimulus. Different spatial arrangements were designed to alter the perceptual organization inferred by the observer without changing the ensemble of chromaticities actually in view. For example, one arrangement of the ten regions was consistent with five surfaces under two distinct illuminations, with one edge within the display (an "apparent illumination edge") dividing the stimulus into two areas, one under illuminant A and the other under illuminant C. Another spatial arrangement had the ten regions configured to induce an observer to infer ten surfaces under a single illumination. When the ten regions were arranged with an apparent illumination edge, the patch within the area of illuminant C was perceived as bluer than when the same patch and immediate surround were presented without an apparent illumination edge. The results are accounted for by positing that observers group together regions sharing the same inferred illumination, with a consequent effect on color perception: A fixed patch-within-surround shifts in hue and saturation toward the perceived illumination. We suggest that the change in color perception in a complex scene that results from a difference in real illumination may be caused by the inferred illumination at the perceptual level, not directly by the physical change in the light absorbed by photoreceptors.
Adult↗
Evaluation of agreement among dermatologists in the assessment of the color of port wine stains and their clearance after treatment with the flashlamp-pumped dye laser.
BACKGROUND: Color classification and its subjective clearance evaluation in response to treatment are essential in the management of patients with port wine stains (PWS). But color perception by physicians is not an objective measurement so that it can change among observers. Agreement among physicians is essential for the reliability of the color classification and the clinical assessment of the response to laser treatment. OBJECTIVE: The purpose of our study was to determine the reliability of the clinical color classification of port wine stains and of their color change or clearance in response to laser treatment. The study was not designed to evaluate the outcome of laser treatment in PWS or the factors that could predict the final response. METHODS: We used the kappa index to evaluate the proportion of agreement in color and clearance perception among dermatologists. Six dermatologists classified the initial color of PWS in 80 patients. Three of them also assessed the amount of clearance achieved after treatment with the flashlamp-pumped dye laser. These three dermatologists were usually dedicated to treat patients with PWS, while the other three were not. RESULTS: The kappa index showed a substantial agreement in both cases. No difference in the initial color perception was observed between the group of dermatologists specialized in PWS and the other three dermatologists. CONCLUSION: These results favor the reliability of the clinical method in the assessment of PWS before and after laser treatment. So, although subjective, color perception by physicians can be used in the study of laser treatment outcome in PWS and its related factors, and the results of different authors can be compared.
Color↗
A vision research apparatus for broad luminance range displays.
Lightness, the perceived gray shade of a surface, and the perception of self-luminous surfaces--that is, surfaces that appear to glow--have most often been studied with paper displays and computer-generated stimuli presented on CRT monitors. Although both methods are often effective, experiments that require a wide range of luminance values in the same display are often difficult to conduct with paper and computer displays alone. Also, color mode appearance is often an issue when surface color perception is the topic of research; CRT monitors are essentially light sources themselves and often appear in the luminous mode of color appearance. Here, we describe an apparatus in which the target is an undetected aperture whose luminance is adjustable. Whereas a typical CRT monitor offers a luminance range of about 100:1, much broader luminance ranges are possible with the described apparatus. Unlike a CRT monitor, the stimulus background will always appear in the surface mode of color perception, and the target(s) can appear as either surface colors or luminous colors. Apparatus modifications are possible, including the addition of a stereoscope or an embedded CRT for creating an adjustable region that is computer controlled.
Color Perception↗
Computer-based training of stimulus detection improves color and simple pattern recognition in the defective field of hemianopic subjects.
In a previously conducted randomized placebo-controlled trial, we were able to demonstrate significant visual field enlargement induced by restitution therapy in patients with cerebral lesions [Kasten, E., Wuest, S., Behrens-Bamann, W., & Sabel, B. A. (1998c). Computer-based training for the treatment of partial blindness. Nature Medicine, 4, 1083-1087.]. Visual field training was performed on a computer monitor for 1 hr per day over a period of 6 months. Since the procedure included only stimulation with white light, in the present study we investigated if this simple detection training had a transfer effect on color or form recognition in the trained area (i.e., in the absence of modality specific training). Answering this question would be crucial for planning optimal restitution therapy: In case there is no transfer of training effects to other visual modalities, a specific treatment of each visual function must be performed in order to achieve maximum benefit. Therefore, we analyzed the data from 32 patients with visual field defects who had participated in the original trial and whose form and color recognition had been investigated. The experimental group (n = 19, restitution training) experienced not only an increase of 12.8% correctly detected stimuli (PeriMa program, p <.05), but also an improvement of 5.6% in pattern recognition (PeriForm) and of 6.1% in color perception (PeriColor), respectively. In contrast, the placebo group (n = 13, fixation training) showed no significant changes from baseline to final outcome in any of the visual modalities (PeriMa: 0.3%; PeriForm: -0.3%; PeriColor: 0.4%). Conventional perimetry yielded an increase of 7.8% detected stimuli in the experimental group, but only of 1.2% in the placebo group (p <.05). For form recognition and color perception, the differences between the results of the experimental and the placebo groups narrowly missed significance. However, correlations of diagnostic results showed that mainly those patients who had achieved visual field enlargement also improved in color and form perception: r =.67 (p <.05) between PeriMa and PeriForm and r =.32 between PeriMa and PeriColor. We conclude that visual restitution training using a simple white light stimulus has at least some influence on improving other visual functions such as color and pattern recognition. This result supports the "bottleneck theory" of visual restitution, i.e., training effects can be explained as a process of perceptual learning and increased processing of information by residual structures surviving lesions of the primary visual pathways.
Audiovisual Aids↗
Perception and the conditioning reflex: vector encoding.
Color perception is dependent on the generation of an excitation vector which, acting on a pool of color detectors (color detector map), produces a corresponding sensation. The generation of the color excitation vector starts at the retinal level, proceeds in the lateral geniculate body, and reaches color detectors at the cortical level. Following processing at the level of declarative memory and semantic maps, results in a verbal categorization of colors. Parallel to the excitation vector pathway, a network computing color differences is operating. The computation of color differences at the retinal level possibly takes place in phasic bipolar cells and progresses in the lateral geniculate body and at the cortical level. Detectors of color differences are assumed to be a basis of respective numerical estimations in humans. Data from frogs, fish, monkeys and humans are compared.
Animals↗
Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words.
In 'colored-hearing' synesthesia, individuals report color experiences when they hear spoken words. If the synesthetic color experience resembles that of normal color perception, one would predict activation of parts of the visual system specialized for such perception, namely the human 'color center', referred to as either V4 or V8. Using functional magnetic resonance imaging (fMRI), we here locate the region activated by speech in synesthetes to area V4/V8 in the left hemisphere, and demonstrate overlap with V4/V8 activation in normal controls in response to color. No activity was detected in areas V1 or V2, suggesting that activity in primary visual cortex is not necessary for such experience. Control subjects showed no activity in V4/V8 when imagining colors in response to spoken words, despite overtraining on word-color associations similar to those spontaneously reported by synesthetes.
Adult↗
Chromatic detection and discrimination in the periphery: a postreceptoral loss of color sensitivity.
The peripheral visual field is marked by a deterioration in color sensitivity, sometimes attributed to the random wiring of midget bipolar cells to cone photoreceptors in the peripheral retina (Mullen, 1991; Mullen & Kingdom, 1996). Using psychophysical methods, we explored differences in the sensitivity of peripheral color mechanisms with detection and discrimination of 2-deg spots at 18-deg eccentricity, and find evidence for a postreceptoral locus for the observed loss in sensitivity. As shown before, observers' sensitivity to green was lower than to red in the periphery, although the magnitude of this effect differed across observers. These results suggest that the asymmetry in peripheral sensitivity occurs at a postreceptoral site, possibly a cortical one. In addition, noise masking was used to determine the cone inputs to the peripheral color mechanisms. The masked detection contours indicate that the red and green mechanisms in the periphery respond to the linear difference of approximately equally weighted L- and M-cone contrasts, just as they do in the fovea. Thus, if the midget retinal ganglion system is responsible for red/green color perception in the fovea, it is likely to be responsible at 18-deg eccentricity as well.
Choice Behavior↗
The perception of surface color.
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Color Perception↗
Motion perception: a color-contingent aftereffect.
When observers who watched repeated alternations of a red contracting spiral and green expanding spiral were later shown stationary spirals, red and a green the red stationary spiral appeared to be expanding and the green stationary spiral appeared to be contracting. These color-contingent motion after effects complement reports of motion-contingent color aftereffects and suggest that both may reflect adaptation of detectors specific to color and motion.
Adolescent↗
Cone inputs in macaque primary visual cortex.
To understand the role of primary visual cortex (V1) in color vision, we measured directly the input from the 3 cone types in macaque V1 neurons. Cells were classified as luminance-preferring, color-luminance, or color-preferring from the ratio of the peak amplitudes of spatial frequency responses to red/green equiluminant and to black/white (luminance) grating patterns, respectively. In this study we used L-, M-, and S-cone-isolating gratings to measure spatial frequency response functions for each cone type separately. From peak responses to cone-isolating stimuli we estimated relative cone weights and whether cone inputs were the same or opposite sign. For most V1 cells the relative S-cone weight was <0.1. All color-preferring cells were cone opponent and their L/M cone weight ratio was clustered around a value of -1, which is roughly equal and opposite L and M cone signals. Almost all cells (88%) classified as luminance cells were cone nonopponent, with a broad distribution of cone weights. Most cells (73%) classified as color-luminance cells were cone opponent. This result supports our conclusion that V1 color-luminance cells are double-opponent. Such neurons are more sensitive to color boundaries than to areas of color and thereby could play an important role in color perception. The color-luminance population had a broad distribution of L/M cone weight ratios, implying a broad distribution of preferred colors for the double-opponent cells.
Action Potentials↗