Topic
Contrast (vision)
About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: Visual acuity was measured in a group of 16 patients with PD, both on and off drugs, and 16 age‐ and sex‐matched normal control subjects and the difference between the two groups was consistent with impaired resolution and could not be accounted for by any perceptual dysfunction that may also have been present in the PD group.
Abstract: Several studies have shown that the visual system is affected in Parkinson's disease (PD) with reduced contrast sensitivity, low-contrast acuity, and flicker sensitivity, as well as altered electroretinograms (ERGs) and pattern visual evoked potentials (VEPs). Apparently, however, no study has yet specifically determined whether visual acuity to high-contrast stimuli is impaired in PD. Visual acuity was measured in a group of 16 patients with PD, both on and off drugs (for 24 h), and 16 age- and sex-matched normal control subjects. Acuity was impaired in the PD group both on standard Snellen chart and on a screen in a computerized test of visual resolution. The degree of impairment was 24 and 25%, respectively, in the two tests. The PD patients had marginally better acuity on both tests while receiving drugs, but the differences were not significant. The difference between the two groups was consistent with impaired resolution and could not be accounted for by any perceptual dysfunction that may also have been present in the PD group. Conversely, however, impaired acuity may be implicated in studies that have reported mild deficits of visuospatial/visuoperceptual function in PD. Reduced acuity appears to be a subtle sequela of dopaminergic deficiency in the visual system.
76 citations
TL;DR: These asymmetries have inborn neural/physiological origins, but can be also susceptible to visual experience, the critical why, and are explained in terms of perceptual aspects or tasks, the what of the asymmetry; and in terms, the why of the underlying mechanisms.
Abstract: Perceptual asymmetry is one of the most important characteristics of our visual functioning. We carefully reviewed the scientific literature in order to examine such asymmetries, separating them into two major categories: within-visual field asymmetries and between-visual field asymmetries. We explain these asymmetries in terms of perceptual aspects or tasks, the what of the asymmetries; and in terms of underlying mechanisms, the why of the asymmetries. Tthe within-visual field asymmetries are fundamental to orientation, motion direction, and spatial frequency processing. between-visual field asymmetries have been reported for a wide range of perceptual phenomena. foveal dominance over the periphery, in particular, has been prominent for visual acuity, contrast sensitivity, and colour discrimination. Tthis also holds true for object or face recognition and reading performance. upper-lower visual field asymmetries in favour of the lower have been demonstrated for temporal and contrast sensitivities, visual acuity, spatial resolution, orientation, hue and motion processing. Iin contrast, the upper field advantages have been seen in visual search, apparent size, and object recognition tasks. left-right visual field asymmetries include the left field dominance in spatial (e.g., orientation) processing and the right field dominance in non-spatial (e.g., temporal) processing. left field is also better at low spatial frequency or global and coordinate spatial processing, whereas the right field is better at high spatial frequency or local and categorical spatial processing. All these asymmetries have inborn neural/physiological origins, the primary why, but can be also susceptible to visual experience, the critical why (promotes or blocks the asymmetries by altering neural functions).
76 citations
TL;DR: Factors shown to be insufficient for explaining human's ability to identify light sources in their visual field are shown and a method for accomplishing the source detection task in the so-called Mondrian world is presented.
Abstract: Experiments show that human beings are capable of detecting self-illuminating surfaces in their visual field, and that this capacity is based, to a great extend, on immediate processing by the visual system, rather than on a higher-level analysis. What are the physical parameters associated with this perception? The following factors are discussed; The highest intensity in the scene, absolute intensity value, local and global contrast, comparison with the average intensity, and lightness computation. All these factors are shown to be insufficient for explaining human's ability to identify light sources in their visual field. Finally, a method for accomplishing the source detection task in the so-called Mondrian world is presented.
76 citations
TL;DR: In this article, the results of a study to assess variations in the indoor and outdoor locomotor mobility of 22 low vision adults were reported, including visual acuity, visual field, and contrast sensitivity data.
Abstract: This article reports the results of a study to assess variations in the indoor and outdoor locomotor mobility of 22 low vision adults. Visual acuity, visual field, and contrast sensitivity data wer...
75 citations
TL;DR: It is suggested that the results of this and previous studies might be explained by the existence of neurons tuned for number.
Abstract: Observers in this study judged which of two fields contained the greater number of spots. Spots had difference-of-Gaussian luminance profiles and could differ in contrast polarity or were of uniform luminance and could differ in size. Weber fractions for all observers except one varied little except when spots varied in size. It is suggested that the results of this and previous studies might be explained by the existence of neurons tuned for number.
75 citations