Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Independent visual threshold measurements in the two eyes of freely moving rats and mice using a virtual-reality optokinetic system.

Abstract: Slow horizontal head and body rotation occurs in mice and rats when the visual field is rotated around them, and these optomotor movements can be produced reliably in a virtual-reality system. If one eye is closed, only motion in the temporal-to-nasal direction for the contralateral eye evokes the tracking response. When the maximal spatial frequency capable of driving the response ("acuity") was measured under monocular and binocular viewing conditions, the monocular acuity was identical to the binocular acuity measured with the same rotation direction. Thus, the visual capabilities of each eye can be measured under binocular conditions simply by changing the direction of rotation. Lesions of the visual cortex had no effect on the acuities measured with the virtual optokinetic system, whereas perceptual thresholds obtained previously with the Visual Water Task are. The optokinetic acuities were also consistently lower than acuity estimates from the Visual Water Task, but contrast sensitivities were the same or better. These data show that head-tracking in a virtual optokinetic drum is driven by subcortical, lower frequency, and contralateral pathways.

How does visual impairment affect performance on tasks of everyday life? The SEE Project

Abstract: Objective To determine the association between performance on selected tasks of everyday life and impairment in visual acuity and contrast sensitivity. Methods Visual acuity and contrast sensitivity were obtained on a population-based sample of 2520 older African American and white subjects. Performance was assessed on mobility, daily activities with a strong visual component, and visually intensive tasks. Disability was defined as performance less than 1 SD below the mean. Receiver operating characteristic curve analyses were used to evaluate the sensitivity and specificity of thresholds in acuity and contrast loss for determining disability. Results Both visual acuity and contrast sensitivity loss were associated with decrements in function. The relationship of function to the vision measures was mostly linear, therefore, receiver operating characteristic curves were not helpful in identifying cutoff points for predicting disabilities. For mobility tasks, most persons were not disabled until they had significant acuity loss (logMAR visual acuity >1.0 or Conclusions Both contrast sensitivity and visual acuity loss contribute independently to deficits in performance on everyday tasks. Defining disability as deficits in performance relative to a population, it is possible to identify visual acuity and contrast loss where most are disabled. However, the cutoff points depend on the task, suggesting that defining disability using a single threshold for visual acuity or contrast sensitivity loss is arbitrary.

Assessment of display performance for medical imaging systems: executive summary of AAPM TG18 report.

Abstract: Digital imaging provides an effective means to electronically acquire, archive, distribute, and view medical images. Medical imaging display stations are an integral part of these operations. Therefore, it is vitally important to assure that electronic display devices do not compromise image quality and ultimately patient care. The AAPM Task Group 18 (TG18) recently published guidelines and acceptance criteria for acceptance testing and quality control of medical display devices. This paper is an executive summary of the TG18 report. TG18 guidelines include visual, quantitative, and advanced testing methodologies for primary and secondary class display devices. The characteristics, tested in conjunction with specially designed test patterns (i.e., TG18 patterns), include reflection, geometric distortion, luminance, the spatial and angular dependencies of luminance, resolution, noise, glare, chromaticity, and display artifacts. Geometric distortions are evaluated by linear measurements of the TG18-QC test pattern, which should render distortion coefficients less than 2%/5% for primary/secondary displays, respectively. Reflection measurements include specular and diffuse reflection coefficients from which the maximum allowable ambient lighting is determined such that contrast degradation due to display reflection remains below a 20% limit and the level of ambient luminance (Lamb) does not unduly compromise luminance ratio (LR) and contrast at low luminance levels. Luminance evaluation relies on visual assessment of low contrast features in the TG18-CT and TG18-MP test patterns, or quantitative measurements at 18 distinct luminance levels of the TG18-LN test patterns. The major acceptable criteria for primary/ secondary displays are maximum luminance of greater than 170/100 cd/m2, LR of greater than 250/100, and contrast conformance to that of the grayscale standard display function (GSDF) of better than 10%/20%, respectively. The angular response is tested to ascertain the viewing cone within which contrast conformance to the GSDF is better than 30%/60% and LR is greater than 175/70 for primary/secondary displays, or alternatively, within which the on-axis contrast thresholds of the TG18-CT test pattern remain discernible. The evaluation of luminance spatial uniformity at two distinct luminance levels across the display faceplate using TG18-UNL test patterns should yield nonuniformity coefficients smaller than 30%. The resolution evaluation includes the visual scoring of the CX test target in the TG18-QC or TG18-CX test patterns, which should yield scores greater than 4/6 for primary/secondary displays. Noise evaluation includes visual evaluation of the contrast threshold in the TG18-AFC test pattern, which should yield a minimum of 3/2 targets visible for primary/secondary displays. The guidelines also include methodologies for more quantitative resolution and noise measurements based on MTF and NPS analyses. The display glare test, based on the visibility of the low-contrast targets of the TG18-GV test pattern or the measurement of the glare ratio (GR), is expected to yield scores greater than 3/1 and GRs greater than 400/150 for primary/secondary displays. Chromaticity, measured across a display faceplate or between two display devices, is expected to render a u',v' color separation of less than 0.01 for primary displays. The report offers further descriptions of prior standardization efforts, current display technologies, testing prerequisites, streamlined procedures and timelines, and TG18 test patterns.

Contrast gain control in the cat visual cortex

Abstract: The eye functions effectively over an enormous range of ambient illumination, because retinal sensitivity can be adapted to prevailing light levels1,2. Higher order neurones in the visual pathway are presumably more concerned with relative changes in illumination, that is, contrast, because a great deal of information concerning absolute light level is processed at the retinal level3. It would therefore be of considerable functional value if cells in the visual cortex could adapt their response levels to a steady-state ambient contrast, in a manner analogous to the sensitivity control mechanism of the retina. We have examined here the idea that adaptation of neurones in the visual cortex to ambient contrast is similar to adaptation in the retina to ambient illumination. The experiments were performed by measuring contrast response functions (response amplitude as a function of contrast) of striate neurones, while systematically adapting them to different contrast levels. Our results show that, for the majority of cortical neurones, response–contrast curves are laterally shifted along a log-contrast axis so that the effective domains of neurones are adjusted to match prevailing contrast levels. This contrast gain control mechanism, which was not observed for lateral geniculate (LGN) fibres, must be of prime importance to visual function.

Contrast sensitivity, acuity, and the perception of 'real-world' targets.

Abstract: A major assumption underlying the use of contrast sensitivity testing is that it predicts whether a patient has difficulty seeing objects encountered in everyday life. However, there has been no large-scale attempt to examine whether this putative relationship actually exists. We have examined this assumption using a clinic based sample of adults aged 20-77 years. Contrast thresholds were measured for both: (1) gratings of 0.5-22.8 cycles/degree; and (2) real-world targets (faces, road signs, objects). Multiple regression techniques indicated that the best predictors of thresholds for real-world targets were age and middle to low spatial frequencies. Models incorporating these variables accounted for 25-40% of the variance. Although acuity significantly correlated with thresholds for real-world targets, the inclusion of acuity as a predictor variable did not improve the model. These data provide direct evidence that spatial contrast sensitivity can effectively predict how well patients see targets typical of everyday life.