Visual processing of color and shape in people with leprosy

Abstract The aim of this study was to analyze the contrast sensitivity of spatial luminance and the color discrimination thresholds of the protan, deutan, and tritan axes of people with leprosy. This study included 8 subjects with leprosy (M = 4, W = 4, M = 33.38 ± 8.7) and 8 healthy subjects (M = 4, W = 4, M = 30.89 ± 5.8). The contrast sensitivity was evaluated by the Metropsis software version 11.0 with vertical sinusoidal grids of frequencies of 0.2, 0.5, 1, 5, 10, and 16 cycles per degree of visual angle (cpd) and color vision by the desaturated Lanthony D15 tests and the trivector and ellipse protocols of the Cambridge Color Test. The results showed significant differences between the groups in the processing of spatial frequencies of 0.2 (U = 14; p = .018); 5.0 (U = 45.0; p = .001); 10.0 (U = 45.0; p = .001), and 16.0 (U = 45.0; p = .001) cpd. The difference in color recognition through D15d (U = 4.0; p = .002). Ellipse 2 (U = 10.0; p = .012) and ellipse 3 (U = 9.0; p = .009) were discriminated against. Overall, the results indicate that leprosy changes the visual processing of low, medium, and high spatial frequencies, as well as the sensitivity of the short wavelength (tritan line of confusion) and long (protan line of confusion) cones.

Chromatic and luminance sensitivity for skin and skinlike textures.

Despite the importance of the appearance of human skin for theoretical and practical purposes, little is known about visual sensitivity to subtle skin-tone changes, and whether the human visual system is indeed optimized to discern skin-color changes that confer some evolutionary advantage. Here, we report discrimination thresholds in a three-dimensional chromatic-luminance color space for natural skin and skinlike textures, and compare these to thresholds for uniform stimuli of the same mean color. We find no evidence that discrimination performance is superior along evolutionarily relevant color directions. Instead, discriminability is primarily determined by the prevailing illumination, and discrimination ellipses are aligned with the daylight locus. More specifically, the area and orientation of discrimination ellipses are governed by the chromatic distance between the stimulus and the illumination. Since this is true for both uniform and textured stimuli, it is likely to be driven by adaptation to mean stimulus color. Natural skin texture itself does not confer any advantage for discrimination performance. Furthermore, we find that discrimination boundaries for skin, skinlike, and scrambled skin stimuli are consistently larger than those for uniform stimuli, suggesting a possible adaptation to higher order color statistics of skin. This is in line with findings by Hansen, Giesel, and Gegenfurtner (2008) for other natural stimuli (fruit and vegetables). Human observers are also more sensitive to skin-color changes under simulated daylight as opposed to fluorescent light. The reduced sensitivity is driven by a decline in sensitivity along the luminance axis, which is qualitatively consistent with predictions from a Von Kries adaptation model.

Prior Knowledge about Objects Determines Neural Color Representation in Human Visual Cortex.

To create subjective experience, our brain must translate physical stimulus input by incorporating prior knowledge and expectations. For example, we perceive color and not wavelength information, and this in part depends on our past experience with colored objects ( Hansen et al. 2006; Mitterer and de Ruiter 2008). Here, we investigated the influence of object knowledge on the neural substrates underlying subjective color vision. In a functional magnetic resonance imaging experiment, human subjects viewed a color that lay midway between red and green (ambiguous with respect to its distance from red and green) presented on either typical red (e.g., tomato), typical green (e.g., clover), or semantically meaningless (nonsense) objects. Using decoding techniques, we could predict whether subjects viewed the ambiguous color on typical red or typical green objects based on the neural response of veridical red and green. This shift of neural response for the ambiguous color did not occur for nonsense objects. The modulation of neural responses was observed in visual areas (V3, V4, VO1, lateral occipital complex) involved in color and object processing, as well as frontal areas. This demonstrates that object memory influences wavelength information relatively early in the human visual system to produce subjective color vision.

The discrimination of chromatic textures.

Color discrimination is influenced by chromatic distributions such as they appear on differently illuminated 3D surfaces (T. Hansen, M. Giesel, & K. R. Gegenfurtner, 2008). Here, we measured discrimination thresholds for chromatically variegated stimuli and modeled the data employing a model with multiple chromatic mechanisms. Each mechanism has a differently tuned half-wave-rectified cosine-shaped sensitivity profile centered at a different chromatic direction. To estimate thresholds, the model's responses to a test and a comparison stimulus are determined. A detection variable is calculated by taking the difference of the responses to the two stimuli and by a subsequent nonlinear combination of the responses. The model was fitted to the data presented in T. Hansen et al. (2008) and to data from two new experiments. In the first experiment, we measured discrimination thresholds for stimuli chromatically variegated along a direction orthogonal to the one used in the previous experiments. In the second experiment, we investigated the interplay between chromatic distributions and different mean contrast levels. We found that a model with eight mechanisms accounted for the effect of chromatic variation within the stimuli and provided a better fit to the discrimination thresholds than a four mechanisms model.

Um sistema de cores na caracterizaçäo biopsicossocial do portador de hanseníase reacional / Color system in the caracterization biopsychosocial of patients with reactional hansen's disease

A questäo norteadora deste estudo é a preocupaçäo com a problemática relacionada à assistência de enfermagem ao portador de hanseníase, especialmente quando surge o fenômeno reacional. Teve como objetivos caracterizar uma amostra de portador de hanseníase reacional, enfatizando aspectos da doença e da reaçäo hansênica e investigar, por meio de um sistema de cores, as principais mudanças ocorridas no âmbito biopsicossocial. Trata-se de um estudo descritivo-exploratório realizado em um hospital-escola que desenvolve um Programa de Controle da Hanseníase, com 28 pacientes adultos de ambos os sexos, em estado reacional, que estavam agendados para atendimento no referido Programa. Foram utilizados 2 instrumentos de coleta de dados: uma entrevista tendo por guia um formulário, contendo questões a serem respondidas oralmente pelos pacientes e um roteiro sobre as mudanças experimentadas pelo cliente em decorrência à crise reacional, onde o mesmo fazia uma síntese, através de um sistema de cores. O período da coleta de dados foi de outubro de 1997 à março de 1998. Obteve-se que as crise reacionais ocorrem em portador de hanseníase de ambos os sexos, independente da idade e do tipo de forma clínica da doença, permanecendo aos cuidados dos serviços de saúde em até cinco anos após a alta quimioterápica. Verifiocou-se que as crises reacionais, alteram consideravelmente a qualidade de vida do seu portador, sinalizadas pela anotações das cores verde, amarela e vermelha, denotando as dificuldades encontradas para lidar com determinados problemas levantados, como a convivência com a dor, as expectativas do sonho de futuro, a alimentaçäo, o sono, entre outros, no seu cotidiano de vida. O sistema de cores utilizado facilitou a anamnese e a análise dos componentes comprometidos, oferecendo subsídios para uma assistência de enfermagem mais eficaz e voltada para as necessidades individuais deste paciente