Saturation-specific pattern of acquired colour vision deficiency in two clinical populations revealed by the method of triads

Subjective colour spaces were reconstructed for persons occupationally exposed to mercury (Hg) and patients with diabetes mellitus type 2, two groups at risk for acquired colour-vision deficiency, and compared with healthy normal trichromats. Judgments of colour dissimilarity were collected with the method of triads, applied to a composite assortment of colour samples. These were drawn from two widely used colour arrangement tests—10 hues from the Farnsworth D-15 test and five from the Lanthony Desaturated D-15d test, ensuring that the assortment sampled two levels of lightness and saturation. The data were analyzed with maximum-likelihood multidimensional scaling (MDS) and within a novel individual-differences MDS model to estimate subject-specific parameters. The MDS solutions for the two clinical groups showed a compression along a blue-yellow axis, limited however to desaturated hues. This result was confirmed by the individual-differences model. In addition, the clinical groups were found to place significantly higher weights on the lightness differences between stimuli, conceivably to compensate for their reduced chromatic discrimination. The specific form of colour-space distortion in the clinical groups indicated an increase in their thresholds for blue-yellow signals, providing insights into the nature of impairment mechanisms. The results have implications for stimuli and diagnostic procedures for testing individual differences in color vision, and for analyzing the responses. This approach is sensitive to distinctive patterns of subtle colour-vision impairment underestimated by the conventional D-15d test

Color space distortions in patients with type 2 diabetes mellitus

Color vision impairment was examined in patients with type 2 diabetes mellitus (DM2) without retinopathy. We assessed the type and degree of distortions of individual color spaces. DM2 patients (n = 32), and age-matched controls (n = 20)were tested using the Farnsworth D-15 and the Lanthony D-15d tests. In addition, subsets of caps from both tests were employed in a triadic procedure (Bimler & Kirkland, 2004). Matrices of inter-cap subjective dissimilarities were estimated from each subject’s “odd-one-out” choices, and processed using non-metric multidimensional scaling. Two-dimensional color spaces, individual and group (DM2 patients; controls), were reconstructed, with the axes interpreted as the R0G and B0Y perceptual opponent systems. Compared to controls, patient results were not significant for the D-15 and D-15d. In contrast, in the triadic procedure the residual distances were significantly different compared to controls: right eye, P 0.021, and left eye, P 0.022. Color space configurations for the DM2 patients were compressed along the B0Y and R0G dimensions. The present findings agree with earlier studies demonstrating diffuse losses in early stages of DM2. The proposed method of testing uses color spaces to represent discrimination and provides more differentiated quantitative diagnosis, which may be interpreted as the perceptual color system affected. In addition, it enables the detection of very mild color vision impairment that is not captured by the D-15d test. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes and thereby to support a treatment strategy

Superstructure Detection in Nucleosome Distribution Shows Common Pattern within a Chromosome and within the Genome

Nucleosome positioning plays an important role in crucial biological processes such as replication, transcription, and gene regulation. It has been widely used to predict the genome’s function and chromatin organisation. So far, the studies of patterns in nucleosome positioning have been limited to transcription start sites, CTCFs binding sites, and some promoter and loci regions. The genome-wide organisational pattern remains unknown. We have developed a theoretical model to coarse-grain nucleosome positioning data in order to obtain patterns in their distribution. Using hierarchical clustering on the auto-correlation function of this coarse-grained nucleosome positioning data, a genome-wide clustering is obtained for Candida albicans. The clustering shows the existence beyond hetero- and eu-chromatin inside the chromosomes. These non-trivial clusterings correspond to different nucleosome distributions and gene densities governing differential gene expression patterns. Moreover, these distribution patterns inside the chromosome appeared to be conserved throughout the genome and within species. The pipeline of the coarse grain nucleosome positioning sequence to identify underlying genomic organisation used in our study is novel, and the classifications obtained are unique and consistent

A computer-controlled color vision test for children based on the Cambridge Colour Test

The present study aimed at providing conditions for the assessment of color discrimination in children using a modified version of the Cambridge Colour Test (CCT, Cambridge Research Systems Ltd., Rochester, UK). Since the task of indicating the gap of the Landolt C used in that test proved counterintuitive and/or difficult for young children to understand, we changed the target Stimulus to a patch of color approximately the size of the Landolt C gap (about 7 degrees Of Visual angle at 50 cm from the monitor). The modifications were performed for the CCT Trivector test which measures color discrimination for the protan, deutan and tritan confusion lines. Experiment I Sought to evaluate the correspondence between the CCT and the child-friendly adaptation with adult subjects (n = 29) with normal color vision. Results showed good agreement between the two test versions. Experiment 2 tested the child-friendly software with children 2 to 7 years old (n = 25) using operant training techniques for establishing and maintaining the subjects` performance. Color discrimination thresholds were progressively lower as age increased within the age range tested (2 to 30 years old), and the data-including those obtained for children-fell within the range of thresholds previously obtained for adults with the CCT. The protan and deutan thresholds were consistently lower than tritan thresholds, a pattern repeatedly observed in adults tested with the CCT. The results demonstrate that the test is fit for assessment of color discrimination in young children and may be a useful tool for the establishment of color vision thresholds during development

Espaço de cores

O artigo apresenta definições para os termos espaço de cores e sistemas de cores; classifica, de acordo com David Brainard (2003), os sistemas de cores em dois grupos: aparência de cores e diferenças de cores. Dentre os diversos sistemas de cores existentes, o artigo descreve dois deles: o sistema de cores Munsell &– um dos mais utilizados entre os sistemas de aparência de cores &– e a descrição do sistema de cores CIE 1931 &– um dos mais utilizados dentre os sistemas de diferença de cores. Faz-se uma retrospectiva histórica da busca por espaços de cores que representem a percepção de cores humana assim como as diversas reconstruções de espaços de cores por métodos eletrofisiológicos ou psicofísicos. Muitas dessas reconstruções utilizam a escala multidimensional (mds). O artigo também introduz a possibilidade da reconstrução dos espaços de cores de pacientes com discromatopsia adquirida como uma distorção do espaço de indivíduos tricromatas normais

Color space

L'article présente des définitions de l'espace de couleur et du système de couleur; selon David Brainard (2003), il classifie les systèmes de couleur en deux groupes: l'aspect de couleur et la différence de couleur. Parmi les systèmes de couleur existants, l'article présente la description de deux d'entre eux: le Système de Couleur de Munsell, l'un des plus utilisés parmi les systèmes d'aspect de couleur, et la description de CIE 1931, l'un des systèmes de différence de couleur les plus utilisés. L'article présente une rétrospective historique de la recherche des espaces de couleur qui représentent la perception humaine de la couleur aussi bien que diverses reconstructions des espaces de couleur, par l'emploi des méthodes d'électrophysiologie et de psychophysique. Plusieurs de ces reconstructions emploient l'échelle multidimensionnelle (mds). L'article présente la possibilité de la reconstruction des espaces de couleur chez les patients avec dyschromatopsie acquise comme une déformation des espaces de couleur trichromatiques normaux.The article presents definitions for the terms color space and color system. In agreement with David Brainard (2003), it classifies the color systems in two groups: color appearance and color difference. Amongst the existing color systems, the article also presents the description of the Munsell Color System, one of the most used among the color appearance systems, and of the CIE 1931, one of the most used color difference systems. In addition, an historical retrospect of the search for color spaces that represent the human color perception as well as the reconstruction of color spaces with electrophysiological and psychophysical methods, are described. Many of these reconstructions use the multidimensional scaling methods (mds). Finally, the article presents the possibility for reconstruction of color spaces of patients with acquired dyschromatopsia as a distortion of the color space of normal trichromats.O artigo apresenta definições para os termos espaço de cores e sistemas de cores; classifica, de acordo com David Brainard (2003), os sistemas de cores em dois grupos: aparência de cores e diferenças de cores. Dentre os diversos sistemas de cores existentes, o artigo descreve dois deles: o sistema de cores Munsell & um dos mais utilizados entre os sistemas de aparência de cores & e a descrição do sistema de cores CIE 1931 & um dos mais utilizados dentre os sistemas de diferença de cores. Faz-se uma retrospectiva histórica da busca por espaços de cores que representem a percepção de cores humana assim como as diversas reconstruções de espaços de cores por métodos eletrofisiológicos ou psicofísicos. Muitas dessas reconstruções utilizam a escala multidimensional (mds). O artigo também introduz a possibilidade da reconstrução dos espaços de cores de pacientes com discromatopsia adquirida como uma distorção do espaço de indivíduos tricromatas normais