Topic
Contrast (vision)
About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.
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TL;DR: It is concluded that the retinal deficit of dopamine in Parkinson's disease is reflected in diminished centre/surround inhibition and that these changes are primarily apparent when vision is tested along the tritan axis, because blue cones are sparsely distributed.
Abstract: Luminance contrast sensitivity and colour contrast thresholds were determined in 26 Parkinson patients and 17 normal controls of comparable age. They were psychophysically tested with a colour monitor system. Stimuli consisted of Gaussian enveloped luminance modulated or colour modulated (protan and tritan axis) vertical sine wave gratings with a spatial frequency of 1 cycle/degree. The stimuli subtended 4 degrees in diameter. Thresholds were determined using a two alternative forced choice method. Three different experimental conditions were explored: the detectability of stationary gratings, of moving gratings at velocities of 0, 2.5 and 5.0 cycles/s, and the detectability of horizontal square wave displacement at a frequency of 5 Hz for gratings of specified contrast levels. Intergroup differences were evaluated using two-tailed t tests with Satterthwaite corrections. Consistent and significant differences between normals and patients were found for tritan stimuli in the static and both dynamic conditions, and for luminance contrast stimuli in the displacement condition. Protan stimuli were much less apt to detect differences between the groups. We conclude that the retinal deficit of dopamine in Parkinson's disease is reflected in diminished centre/surround inhibition and that these changes are primarily apparent when vision is tested along the tritan axis, because blue cones are sparsely distributed.
91 citations
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TL;DR: There is a definite difference in legibility between letters at contrast threshold as for letters at acuity threshold, and the very regular and pronounced miscalling of the letter C as an O should be accepted as a correct call during threshold measurements on the Pelli‐Robson chart.
91 citations
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TL;DR: New concepts and mechanisms from a real-time visual processing theory that has been used to explain paradoxical data about brightness and form perception are described.
Abstract: This paper describes new concepts and mechanisms from a real-time visual processing theory that has been used to explain paradoxical data about brightness and form perception. These data include the Craik-O'Brien effect, the Land brightness and color demonstrations, the fading of stabilized images, neon color spreading, complementary color induction, completion of illusory contours, and binocular rivalry. Two functionally distinct contour processes interact to generate these brightness and form properties in the theory. A Boundary Contour process is sensitive to the amount of contrast but not to the direction of contrast in scenic edges. It includes a binocular matching stage that is sensitive to spatial scale, orientation, and binocular disparity, and whose outcome triggers a process of monocular contour completion. These completed contours form the boundaries of monocular perceptual domains. A Feature Contour process is sensitive to both the amount of contrast and to the direction of contrast in scenic edges. It triggers a diffusive filling-in reaction of featural quality within perceptual domains whose boundaries are dynamically defined by the completed boundary contours. The diffusive filling-in reactions take place within syncytia of cell compartments. These preprocessed monocular representations give rise to a percept via a process of binocular resonance. The percept takes the form of standing waves of patterned activity among multiple spatial scales. The Boundary Contour process is hypothesized to be analogous to interactions between the hypercolumns in area 17 of the visual cortex. The Feature Contour process is hypothesized to be analogous to interactions between the cytochrome oxydase staining blobs in area 17 and prestriate cortex in area 18.
91 citations
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TL;DR: A Monte Carlo simulation has been developed to analyze the effects of changes in scattering, index of refraction, and absorption in a three-layer medium and shows that the largest source of contrast is changes in refractive index.
Abstract: The relationship between optical properties and image contrast in confocal imaging is investigated A Monte Carlo simulation has been developed to analyze the effects of changes in scattering, index of refraction, and absorption in a three-layer medium Contrast was calculated from the computed signal-to-background ratios for changes in tissue optical properties Results show that the largest source of contrast is changes in refractive index
91 citations
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TL;DR: The trifocal Fine Vision IOL can restore vision at different distances after cataract surgery, specifically intermediate and near vision.
Abstract: Purpose To evaluate the visual outcomes of patients with a new diffractive trifocal intraocular lens (IOL). Methods A trifocal diffractive Fine Vision IOL (Physiol, Liege, Belgium) was implanted after microincision cataract surgery (MICS) in 40 eyes of 20 patients with bilateral cataract. The monocular and binocular visual performance and the refractive status were assessed, as well as the defocus curve and contrast sensitivity at 1 and 6 months postoperatively. Results The monocular visual outcomes (logMAR) at 6 months postoperatively were uncorrected distance visual acuity 0.18 ± 0.13, uncorrected near visual acuity 0.26 ± 0.15, and uncorrected intermediate visual acuity 0.20 ± 0.11. With the best distance correction, the visual outcomes were 0.05 ± 0.06 for corrected distance visual acuity, 0.16 ± 0.13 for distance corrected near visual acuity, and 0.17 ± 0.09 for distance corrected intermediate visual acuity. Binocular defocus curve at 6 months shows a wide range of useful vision with 0.19 ± 0.08 (logMAR) at -1.50 diopter defocus. The monocular contrast sensitivity under scotopic conditions (3 cd/m(2)) was within normal range for a population older than 60 years. Conclusion The trifocal Fine Vision IOL can restore vision at different distances after cataract surgery, specifically intermediate and near vision.
91 citations