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- The achromatic 'philosophical zombie', a syndrome of cerebral achromatopsia with color anopsognosia. [Journal Article]
- Case Rep Neurol 2013 Jan; 5(1):98-103.
We describe a patient with persistent cerebral achromatopsia occurring after bilateral occipital strokes. Blinded color recognition was assessed with a computerized experimental paradigm and the patient reported the degree of confidence in the response exactness on a visual percent scale. Color recognition was accurate and above chance (Fisher's exact test, p < 0.002). The degree of confidence in the answers showed a significant correlation with recognition scores (Spearman rank order correlation, p < 0.0001). These findings constitute the exceptional condition of what we called color anopsognosia (not knowing of seeing colors) and recall the theoretic figure of the 'philosophical zombie'. However, the cognitive mechanisms of the dissociation between a subjective colorless vision and good performance for color naming still remain poorly understood.
- Automated Analysis of Diabetic Retinopathy Images: Principles, Recent Developments, and Emerging Trends. [JOURNAL ARTICLE]
- Curr Diab Rep 2013 May 18.
Diabetic retinopathy (DR) is a vision-threatening complication of diabetes. Timely diagnosis and intervention are essential for treatment that reduces the risk of vision loss. A good color retinal (fundus) photograph can be used as a surrogate for face-to-face evaluation of DR. The use of computers to assist or fully automate DR evaluation from retinal images has been studied for many years. Early work showed promising results for algorithms in detecting and classifying DR pathology. Newer techniques include those that adapt machine learning technology to DR image analysis. Challenges remain, however, that must be overcome before fully automatic DR detection and analysis systems become practical clinical tools.
- Toxic risks and nutritional benefits of traditional diet on near visual contrast sensitivity and color vision in the Brazilian Amazon. [JOURNAL ARTICLE]
- Neurotoxicology 2013 May 13.
BACKGROUND:Visual functions are known to be sensitive to toxins such as mercury (Hg) and lead (Pb), while omega-3 fatty acids (FA) and selenium (Se) may be protective. In the Tapajós region of the Brazilian Amazon, all of these elements are present in the local diet.
OBJECTIVE:Examine how near visual contrast sensitivity and acquired color vision loss vary with biomarkers of toxic exposures (Hg and Pb) and the nutrients Se and omega-3 FA in riverside communities of the Tapajós.
METHODS:Complete visuo-ocular examinations were performed. Near visual contrast sensitivity and color vision were assessed in 228 participants (≥15 years) without diagnosed age-related cataracts or ocular pathologies and with near visual acuity refracted to at least 20/40. Biomarkers of Hg (hair), Pb (blood), Se (plasma), and the omega-3 FAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in plasma phospholipids were measured. Multiple linear regressions were used to examine the relations between visual outcomes and biomarkers, taking into account age, sex, drinking and smoking.
RESULTS:Reduced contrast sensitivity at all spatial frequencies was associated with hair Hg, while %EPA, and to a lesser extent %EPA+DHA, were associated with better visual function. The intermediate spatial frequency of contrast sensitivity (12 cycles/degree) was negatively related to blood Pb and positively associated with plasma Se. Acquired color vision loss increased with hair Hg and decreased with plasma Se and %EPA.
CONCLUSIONS:These findings suggest that the local diet of riverside communities of the Amazon contain toxic substances that can have deleterious effects on vision as well as nutrients that are beneficial for visual function. Since remediation at the source is a long process, a better knowledge of the nutrient content and health effects of traditional foods would be useful to minimize harmful effects of Hg and Pb exposure.
- In nutrition, can we "see" what is good for us? [Journal Article]
- Adv Nutr 2013; 4(3):327S-34S.
The selection of foods to eat is a complex interplay of vision, taste, smell, and texture. In addition to micro- and macronutrients, plant-based foods also contain several classes of phytochemicals. In many cases, the phytochemicals account for the various colors of foods. Although aesthetically pleasing, the color of foods may mislead consumers as to their phytochemical content, which is particularly true with regard to polyphenols. Polyphenols are a broad class of compounds with antioxidant and other health benefits. Human vision is limited to a small window (390-765 nm) of the electromagnetic spectrum. Many important phytochemicals (e.g., vitamin C) have no absorbance in this range. Therefore, the human eye cannot directly judge the vitamin C content of foods. Being able to see in the ultraviolet range allows bees to locate the pollen-rich region of flowers, whereas pit vipers locate their prey by being able to "see" them in the infrared range. Assessing the impact of phytochemicals on human health depends on several factors. Colorless phytochemicals in unprocessed foods may be lost during the cooking process because no visual guide exists to ensure their retention. The molecular structures of phytochemicals influence the extent to which they are altered by cooking processes and the methods by which they are absorbed from the gastrointestinal tract. Extensive metabolism by phase I/II enzymes and by the gut microbiome may also create compounds that the eye is never allowed to appreciate.
- Evaluation of multimodal imaging in carriers of X-linked retinitis pigmentosa. [JOURNAL ARTICLE]
- Exp Eye Res 2013 May 10.
The aim of this study was to investigate visualization of the tapetal-like reflex using current imaging modalities and evaluate SD-OCT changes in known carriers of X-linked retinitis pigmentosa (XLRP); the objective being the development of an optimal protocol for clinicians to identify carriers. Ten XLRP carriers (19 eyes) were examined using color fundus photography, 488 nm reflectance (488-R), near-infrared reflectance (NIR-R), autofluorescence (AF) and spectral domain optical coherence tomography (SD-OCT) imaging (Spectralis SLO-OCT, Heidelberg). Horizontal line scans through the fovea were acquired in all subjects and in a group of 10 age-similar controls. Peripheral SD-OCT scans (extending to 27.5° eccentricity) were also acquired in both eyes of 7 carriers. MP-1 microperimetery (10-2 pattern; Nidek) was performed in one eye of each carrier. For the XLRP carriers, a tapetal reflex was observed with all imaging modalities in 8 of 19 eyes. It had the same retinal location on color fundus, 488-R and NIR-R imaging but a different location on AF. The tapetal reflex was most easily detected in 488-R images. The horizontal foveal SD-OCT scans were qualitatively normal, but measurements showed significant outer retinal layer thinning in all eyes. Additionally, the 14 eyes with peripheral SD-OCTs demonstrated patchy loss of the inner segment ellipsoid band. Microperimetry exhibited patchy visual sensitivity loss in 9 eyes. Full field ERGs were variable, ranging from normal to severely abnormal rod and cone responses. Our findings suggest that an optimal protocol for identifying carriers of XLRP should include 488-R imaging in a multimodal approach. Peripheral SD-OCT imaging and central retinal layer quantification revealed significant structural abnormalities.
- The Attraction of Yellow Corn: Reduced Attentional Constraints on Coding Learned Conjunctive Relations. [JOURNAL ARTICLE]
- J Exp Psychol Hum Percept Perform 2013 May 13.
Physiological evidence indicates that different visual features are computed quasi-independently. The subsequent step of binding features, to generate coherent perception, is typically considered a major rate-limiting process, confined to one location at a time and taking 25 ms per item or longer (A. Treisman & S. Gormican, 1988, Feature analysis in early vision: Evidence from search asymmetries, Psychological Review, Vol. 95, pp. 15-48). We examined whether these processing limitations remain once bindings are learned for familiar objects. Participants searched for objects that could appear either in familiar or unfamiliar colors. Objects in familiar colors were detected efficiently at rates consistent with simultaneous binding across multiple stimuli. Processing limitations were evident for objects in unfamiliar colors. The advantage for the learned color for known targets was eliminated when participants searched for geometric shapes carrying the object colors and when the colors fell in local background areas around the shapes. The effect occurred irrespective of whether the nontargets had familiar colors, but was largest when nontargets had incorrect colors. The efficient search for targets in familiar colors held, even when the search was biased to favor objects in unfamiliar colors. The data indicate that learned bindings can be computed with minimal attentional limitations, consistent with the direct activation of learned conjunctive representations in vision. (PsycINFO Database Record (c) 2013 APA, all rights reserved).
- Perceived vision-related quality of life and risk of falling among community living elderly people. [Journal Article]
- Scand J Caring Sci 2013 Jun; 27(2):433-9.
Scand J Caring Sci; 2013; 27; 433-439 Perceived vision-related quality of life and risk of falling among community living elderly people Falls and fall injuries among the elderly population are common, since ageing is a risk factor of falling. Today, this is a major problem because the ageing population is increasing. There are predictive factors of falling and visual impairment is one of them. Usually, only visual acuity is considered when measuring visual impairment, and nothing regarding a person's functional visual ability is taken into account. Therefore, the aim of this study was to assess the perceived vision-related quality of life among the community living elderly using the 25-item National Eye Institute Visual Function Questionnaire (NEI VFQ-25) and to investigate whether there was any association among vision-related quality of life and falls. There were 212 randomly selected elderly people participating in the study. Our study indicated that the participants had an impaired perceived vision-related health status. General health was the only NEI VFQ-25 variable significantly associated with falls in both men and women. However, among men, near and distance activities, vision-specific social functioning, role difficulties and dependency, color and peripheral vision were related to falls.
- Color polymorphism in a land snail Cepaea nemoralis (Pulmonata: Helicidae) as viewed by potential avian predators. [JOURNAL ARTICLE]
- Naturwissenschaften 2013 May 8.
Avian predation is one of the most probable factors maintaining polymorphism of shell coloration in Cepaea nemoralis. This assumption is justified by the fact that birds frequently forage on snails and their prey choice varies with morph coloration. However, in all preceding studies, the conspicuousness of morphs was determined only by using human vision which is significantly different from birds' visual perception. In this study, we assessed how birds perceive colors of four Cepaea nemoralis morphs using physiological models of avian color vision. We calculated combined chromatic and achromatic contrast between shells and three habitat background types as a measure of shell conspicuousness. The degree of background color matching in Cepaea nemoralis depended on both shell morph and habitat type. On average, banded morphs were more conspicuous than unbanded morphs. Morphs were the most cryptic against dry vegetation and the most conspicuous on bare ground. We also found a significant interaction between habitat type and color morph. The relative conspicuousness of shell morphs depended on habitat and was the most variable against green vegetation. Our study provides the first insight into how potential avian predators view Cepaea nemoralis morphs. The results are discussed in light of multiple hypotheses explaining selective predation on Cepaea nemoralis morphs.
- Food search through the eyes of a monkey: A functional substitution approach for assessing the ecology of primate color vision. [JOURNAL ARTICLE]
- Vision Res 2013 May 3.:87-96.
Efficient detection and selection of reddish fruits against green foliage has long been thought to be a major selective pressure favoring the evolution of primate trichromatic color vision. This has recently been questioned by studies of free-ranging primates that fail to show predicted differences in foraging efficiency between dichromats and trichromats. In the present study, we use a unique approach to evaluate the adaptive significance of trichromacy for fruit detection by undertaking a functional substitution model. The color vision phenotypes of neotropical monkeys are simulated for human observers, who use a touch-sensitive computer interface to search for monkey food items in digital images taken under natural conditions. We find an advantage to trichromatic phenotypes - especially the variant with the most spectrally separated visual pigments - for red, yellow and greenish fruits, but not for dark (purple or black) fruits. These results indicate that trichromat advantage is task-specific, and that shape, size and achromatic contrast variation between ripe and unripe fruits cannot completely mitigate the advantage of color vision. Similarities in fruit foraging performance between primates with different phenotypes in the wild likely reflect the behavioral flexibility of dichromats in overcoming a chromatic disadvantage.
- Psychophysical contrast calibration. [JOURNAL ARTICLE]
- Vision Res 2013 Apr 30.
Electronic displays and computer systems offer numerous advantages for clinical vision testing. Laboratory and clinical measurements of various functions and in particular of (letter) contrast sensitivity require accurately calibrated display contrast. In the laboratory this is achieved using expensive light meters. We developed and evaluated a novel method that uses only psychophysical responses of a person with normal vision to calibrate the luminance contrast of displays for experimental and clinical applications. Our method combines psychophysical techniques (1) for detection (and thus elimination or reduction) of display saturating non-linearities; (2) for luminance (gamma function) estimation and linearization without use of a photometer; and (3) to measure without a photometer the luminance ratios of the display's three color channels that are used in a bit-stealing procedure to expand the luminance resolution of the display. Using a photometer we verified that the calibration achieved with this procedure is accurate for both LCD and CRT displays enabling testing of letter contrast sensitivity to 0.5%. Our visual calibration procedure enables clinical, internet and home implementation and calibration verification of electronic contrast testing.