Contrast sensitivity measurement in evaluations in visual symptoms caused by exposure to triethylamine
Objectives: To determine whether blurred vision caused by exposure to triethylamine (TEA) can be detected by the measurement of contrast sensitivity. Methods: 41 cold box core makers of three foundries and 82 control workers were examined. A detailed ocular and medical history was obtained from the subjects. The contrast sensitivity of the core makers was measured on Monday and Friday of the same week both before and immediately after work and also on a third day, when air samples of TEA were collected. Contrast sensitivity and visual acuity were measured by optotype figures at full contrast, 2.5% contrast, and 0.6% contrast. The changes in contrast sensitivity were used for the analysis. The results of binocular vision and the results of the dominant eye were analysed. Urine specimens for the analysis of TEA were collected ...http://connection.ebscohost.com/c/articles/8002943/contrast-sensitivity-measurement-evaluations-visual-symptoms-caused-by-exposure-triethylamine
Human Achromatic Spatial Contrast Sensitivity Measured With Transient Visual Evoked Cortical Potential: Comparison With...
Purpose: : To evaluate human achromatic spatial contrast sensitivity (CSF) with transient visual evoked cortical potential (tVECP). To compare electrophysiological and psychophysical measurements. Methods: : Six healthy subjects (21 ± 2 years-old) were monocularly tested. The stimuli were black and white horizontal sinusoidal gratings, 40 cd/m2 mean luminance, presented in a 5º circular patch. Six spatial frequencies were used: 0.4, 0.8, 2, 4, 8, and 10 cycles per degree (cpd), in 1 Hz squarewave reversal mode. Electrophysiological contrast thresholds were estimated by linear regressions fitted to data point representing P100 tVECP amplitude as a function of log contrast, extrapolated to zero amplitude. Psychophysics measurements were performed in the same spatial frequencies plus 1 and 6 cpd, using identical spatio-temporal configuration as used in tVECP experiments (dynamic presentation) and using stationary stimuli (static presentation). ...http://iovs.arvojournals.org/article.aspx?articleid=2395155
Spatial long-range modulation of contrast discrimination | (2000) | Chen | Publications | Spie
Contrast discrimination is an important type of information for establishing image quality metrics based on human vision. We used a dual-masking paradigm to study how contrast discrimination can be influenced by the presence of adjacent stimuli. In a dual masking paradigm, the observer's task is to detect a target superimposed on a pedestal in the presence of flankers. The flankers (1) reduce the target threshold at zero pedestal contrast; (2) reduce the size of pedestal facilitation at low pedestal contrasts; and (3) shift the TvC (Target threshold vs. pedestal contrast) function horizontally to the left on a log-log plot at high pedestal contrasts. The horizontal shift at high pedestal contrasts suggests that the flanker effect is a multiplicative factor that cannot be explained by previous models of contrast discrimination. We extended a divisive inhibition model of ...http://spie.org/Publications/Proceedings/Paper/10.1117/12.389432
Age-related changes in contrast gain related to the M and P pathways | JOV | ARVO Journals
The observed shift in the contrast gain function is consistent with previous measures of spatial vision loss with age. For instance, Sloane, Owsley, and Jackson (1988) measured contrast sensitivity for young and old observers with spatial frequencies ranging from 0.5 to 8 c/deg and luminance levels ranging from mesopic to photopic. At a low temporal frequency, the slope of the sensitivity function (inverse of the threshold function) spanning the range of luminance was steeper for older than younger observers at spatial frequencies below 4 c/deg. This means that older observers required more contrast at low luminance levels to detect a sine-wave grating than their younger counterparts. This pattern of contrast sensitivity loss is consistent with a reduction in the contrast gain slope of the underlying mechanism at low spatial frequencies. In addition, suprathreshold measures ...http://jov.arvojournals.org/article.aspx?articleid=2121305
Aerial perspective - Wikipedia
The ability of a person with normal visual acuity to see fine details is determined by his or her contrast sensitivity. Contrast sensitivity is the reciprocal of the smallest contrast for which a person can see a sine-wave grating. A person's contrast sensitivity function is contrast sensitivity as a function of spatial frequency. Normally, peak contrast sensitivity is at about 4 cycles per degree of visual angle. At higher spatial frequencies, comprising finer and finer lines, contrast sensitivity decreases, until at about 40 cycles per degree even the brightest of bright lines and the darkest of dark lines cannot be seen.. The high spatial frequencies in an image give it its fine details. Reducing the contrast of an image reduces the visibility of these high spatial ...https://en.wikipedia.org/wiki/Atmospheric_perspective
Contrast Sensitivity With a Subretinal Prosthesis and Implications for Efficient Delivery of Visual Information | IOVS | ARVO...
Purpose: To evaluate the contrast sensitivity of a degenerate retina stimulated by a photovoltaic subretinal prosthesis, and assess the impact of low contrast sensitivity on transmission of visual information. Methods: We measure ex vivo the full-field contrast sensitivity of healthy rat retina stimulated with white light, and the contrast sensitivity of degenerate rat retina stimulated with a subretinal prosthesis at frequencies exceeding flicker fusion (,20 Hz). Effects of eye movements on retinal ganglion cell (RGC) activity are simulated using a linear-nonlinear model of the retina. Results: Retinal ganglion cells adapt to high frequency stimulation of constant intensity, and respond transiently to changes in illumination of the implant, exhibiting responses to ON-sets, OFF-sets, and both ON- and OFF-sets of light. The percentage of cells with an OFF response decreases ...http://iovs.arvojournals.org/article.aspx?articleid=2469219
Surround suppression between S-cone and luminance signals measured with psychophysics and source-imaged EEG | JOV | ARVO...
Purpose: To characterize the interaction of S-cone driven signals and luminance signals in the early visual pathways and in perception, we used psychophysics and source-imaged EEG to measure surround suppression (SS) of S-cone signals, luminance signals and the interactions between them.. Psychophysics: Observers were asked to match the contrast level of a test stimulus to that of a target. The target was a Gabor patch presented in isolation and the test was a similar Gabor patch presented either in isolation or within an annular surround. The probe and surround were defined by either S-cone or luminance contrast. The probe flashed at 6Hz and the surround drifted at 5cpd. The relative orientation of the probe and the surround were either co-linear or orthogonal to each other. For collinear conditions, the results showed that S-cone surrounds suppressed the apparent contrast of S-cone probes by 40% and luminance surrounds also suppressed luminance probes by ...http://jov.arvojournals.org/article.aspx?articleid=2136525
Contrast sensitivity is fundamental to natural visual processing and an important tool for characterizing both visual function and clinical disorders. We simultaneously measured contrast sensitivity and neural contrast response functions and compared measurements in common laboratory conditions with naturalistic conditions. In typical experiments, a subject holds fixation and a stimulus is flashed on, whereas in natural vision, saccades bring stimuli into view. Motivated by our previous V1 findings, we tested the hypothesis that perceptual contrast sensitivity is lower in natural vision and that this effect is associated with corresponding changes in V1 activity. We found that contrast sensitivity and V1 activity are correlated and that the relationship is similar in laboratory and naturalistic paradigms. However, in the more natural situation, ...http://jn.physiology.org/content/117/2/492
Some multiple sclerosis patients with 20/20 acuity complain of poor vision. In a previous report we accounted for this in our patient group by showing that multiple sclerosis had caused a depression of contrast sensitivity while sparing visual acuity. In this study we investigated whether some of this measured depression might be due to abnormally rapid or severe adaptation during the test procedure rather than a true permanent loss. Our finding was opposite to this supposition: adaptation was abnormally slight and/ or slow.. Depressed contrast sensitivity was not well correlated with abnormal adaptation to contrast. In patients whose contrast sensitivity losses were restricted to a band of spatial frequencies, we found no evidence that abnormalities of contrast adaptation were restricted to this same spatial frequency band. Further evidence of dissociation between abnormal ...https://www.cambridge.org/core/search?filters%5BauthorTerms%5D=T.J.%20Murray&eventCode=SE-AU
British Library EThOS: Perceptual learning of contrast discrimination and its neural correlates in macaque V4 and V1
We make frequent evaluations of subtle contrast differences in our visual environment, and often under challenging illumination conditions, whether photopic, scotopic or mesopic. Our contrast discrimination abilities are rigorously honed from an early age, and we continue to carry out these fine perceptual judgments throughout our lifetimes. Thus, the issue of whether substantial improvement in contrast discrimination is possible during later periods in life, such as during adulthood- and the circumstances that allow this- has sometimes come under discussion. Our adult macaque subjects underwent extensive training on a contrast discrimination task, in which stimuli were positioned at a variety of peripheral and parafoveal locations. We present clear evidence of contrast perceptual learning at the behavioural level and show that these changes have neuronal correlates primarily in V4, rather than in V1. Learning was specific ...http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627705
Human contrast sensitivity to visual patterns vs. model | Open-i
Human contrast sensitivity to visual patterns vs. model predictions.a, Probability distribution of the 512 possible 3×3 1-bit pixel patterns (grey histogram).https://openi.nlm.nih.gov/detailedresult.php?img=PMC3716808_pone.0069154.g003&req=4
Contrast gain-control in stereo depth and cyclopean contrast perception | JOV | ARVO Journals
A two-interval forced choice (2-IFC) task was used to measure disparity threshold. Each trial began with a fixation image (Figure 3a), consisting of a dark fixation dot (diameter of 6.25 min) in the center of a random-dot background (Michelson contrast = 0.2). The vertical and horizontal positions of the two monocular images could be adjusted manually to achieve better convergence in the beginning of each block. After successfully combining the two monocular images into one steady cyclopean image, observers pressed the space bar on the computer keyboard to start the presentation of a 1300-ms dynamic RDS movie. The movie contained two 400-ms stimulus intervals, each consisting of eight frames of independently sampled RDS and delimited by a brief tone in the beginning and a 500-ms interstimulus interval. Dynamic RDS with zero disparity was presented during the 500-ms interstimulus interval. The RDS in one of the randomly chosen intervals contained a horizontal disparity in the lower half of ...http://jov.arvojournals.org/article.aspx?articleid=2193991
Phase 3 Intravitreous Bevacizumab and Standard Metabolic Control for Diabetic Macular Edema - A Contrast Sensitivity Pilot...
To evaluate the effects on contrast sensitivity (CS) measurements of intravitreal bevacizumab injections associated with standard metabolic control in eyeshttp://adisinsight.springer.com/trials/700252103?error=cookies_not_supported&code=7a0edd6f-7267-4491-8b78-19bd13dc424c
Visual Contrast Sensitivity Test - Toxicity Testing | Brant A. Larsen, D.C.
With the increasing rise of toxicity, and the increasing awareness of this huge problem, we need to have ways of determining which patients are likely to bhttp://drlarsen.com/visual-contrast-sensitivity-test-toxicity-testing/
Abnormal scanpaths in visual search correlate with contrast sensitivity deficits in schizophrenia - Nuffield Department of...
Enrichment of Macular Pigment Enhances Contrast Sensitivity in Subjects Free of Retinal Disease: Central Retinal Enrichment...
This brings us to the second, and seemingly more plausible mechanism for our observations. The seminal work of Kuffler,46 and several subsequent investigations,47 have characterized the anatomic and neurophysiologic basis for CS lateral inhibition. In short, lateral inhibition is the result of retinal circuitry that is wired in such a way as to produce many thousands of overlapping, roughly concentric, subtractive regions called receptive fields.48 Light differentially affects the center versus surround regions of the receptive field and, ultimately, the perceived difference between the two yields the visual system's ability to detect edges (i.e., contrast). The arrangement of the receptive fields is such that a difference in CS is a function of spatial frequency, and this phenomenon is known as the contrast sensitivity function (CSF), and, when tested with sinusoidal gratings, its peak generally is found to be approximately 4 cycles/deg (although the ...http://iovs.arvojournals.org/article.aspx?articleid=2532328
A computational study of brightness-related responses in visual cortex | JOV | ARVO Journals
Previous experimental studies have reported that V1 neurons can respond to a region of uniform luminance (Kinoshita & Komatsu, 2001; Friedman et al., 2003; Roe et al., 2005). Some V1 neurons even show responses modulated by the luminance change of surrounding areas, or flankers that are several degrees away from the their CRFs, while the luminance of the area that covers their CRFs stays constant (Rossi et al., 1996; Rossi & Paradiso, 1999). Some of these neurons show responses that are antiphase to the luminance change of flankers, but show responses in-phase to direct luminance change. These responses are consistent with the human perception of brightness. The modulation of these neurons' responses to the simultaneous contrast stimuli cut off at 4 Hz, while the modulation of their responses to direct luminance increases with temporal frequency of the luminance change, which is also consistent to the result shown in human psychophysical studies (Valois, Webster, Valois, & Lingelbach, 1986; ...http://jov.arvojournals.org/article.aspx?articleid=2121505
Rod spatial channels and adult aging: Implications for analysis of development of infant spatial vision | JOV | ARVO Journals
PURPOSE. We extracted spatial channels underlying scotopic contrast sensitivity functions (CSFs) of normal adult observers, and compared them to channels underlying photopic contrast sensitivity functions. METHODS. Scotopic CSFs were measured on 50 observers between the ages of 20 and 88 years (Schefrin et al. 1999). These CSFs were measured psychophysically using 2AFC at 7 spatial frequencies ranging from 0.2 to 3.0 c/deg, with mean retinal illuminance equated for observers at −0.85 log scotopic Trolands. RESULTS. A covariance analysis of individual differences was applied to the data. We computed statistical sources of individual variability, used them to define "covariance channels," and determined the number and frequency tuning of these channels. We found evidence for 3 discrete channels operating below 3 c/deg. Two covariance channels operated primarily above 1 c/deg, and were predicted and well fit by a computational model of photopic ...http://jov.arvojournals.org/article.aspx?articleid=2191466
Infant Contrast Sensitivity: Contributions of Factors Related to Visual Experience vs. Preprogrammed Mechanisms | JOV | ARVO...
In order to investigate potential effects of visual experience vs. preprogrammed mechanisms on visual development, we have investigated how well variation in contrast sensitivity (CS) across a large group of typical infants (n = 182) can be accounted for by a variety of factors that differ in the extent to which they are tied to visual experience. Using multiple regression analyses, we find that gestational length and gender, which are unlikely to be tied to visual experience, predict Luminance CS (thought to be mediated by the Magnocellular pathway). Other factors, which might be tied to either preprogrammed mechanisms or visual experience, specifically, birth order and small variations in postnatal age, predict Chromatic CS (thought to be mediated by the Parvocellular pathway) and Luminance CS. In addition, we have investigated effects of visual experience vs. preprogrammed mechanisms by studying CS in infant twins (n = 64). Our results show that the CS of both monozygotic ...http://jov.arvojournals.org/article.aspx?articleid=2138234
Crowding and surround suppression: Not to be confused | JOV | ARVO Journals
Crowding and surround suppression share many similarities, which suggests the possibility of a common mechanism. Despite decades of research, there has been little effort to compare the two phenomena in a consistent fashion. A recent study by D. M. Levi, S. Hariharan, and S. A. Klein (2002) argues that the two are unrelated because crowding effects can be much stronger than suppression effects. Here we report experiments in which the same Gabor target was used both for orientation identification (crowding) and contrast detection (suppression) tasks. In agreement with early crowding studies (e.g., H. Bouma, 1973) we found, that an outward mask is much more effective than an inward mask for the orientation identification task. Notably, no such anisotropy was observed for the contrast detection task, commonly used to measure surround suppression. The anisotropic masking, which defines crowding, is observed only at fine scales (roughly within an octave of the acuity limit), ...http://jov.arvojournals.org/article.aspx?articleid=2121959
Brief presentation enhances various simultaneous contrast effects | JOV | ARVO Journals
All stimuli were generated using the MATLAB (The MathWorks, MA) programming environment with Psychtoolbox (Brainard, 1997; Pelli, 1997) routines. The test stimulus whose orientation was to be judged was a sinusoidal grating with a hard-edged circular window (3° diameter). It was embedded at the center of a larger disk filled with a sinusoidal grating (8° diameter, the surround). Both grayscale gratings had a spatial frequency of 2 c/° and a luminance contrast of 100%. The test grating was always vertical (=0° hereafter). To aid the visibility of the test grating, the relative spatial phase difference between the test grating and the surrounding grating was always fixed at 1/4 pi (45°) although the absolute spatial phase was chosen randomly for each trial. Orientations of the surround were varied from 3° to 19° with a 2° step, both clockwise and counterclockwise, resulting in 18 conditions. The comparison grating was identical to the test grating except that its orientation was ...http://jov.arvojournals.org/article.aspx?articleid=2621973&resultClick=1
OSA | Multiresolution local contrast enhancement of x-ray images for poultry meat inspection
A multiresolution-analysis-based local contrast transform is proposed to enhance local structures in x-ray images. The local contrast is defined as a ratio of the local intensity variation to the local mean. With wavelet multiresolution decomposition, the detail coefficients and approximation coefficients are interpreted, respectively, as local variations and local averages in virtue of the localization property of wavelet transform. Based on the local contrast transform, an algorithm is developed to modify coefficients before wavelet synthesis. An across-scale local contrast is obtained when the scale associated with the local variation is different from that of the local mean. The nonlinearity and local adaptiveness properties of local contrast transform result in structural enhancement in local dark regions in the reconstructed images. We applied this technique to deboned poultry inspection using x-ray images. Because of ...https://www.osapublishing.org/ao/abstract.cfm?uri=ao-40-8-1195
WaveLight® Refractive Flap Accuracy Study - Full Text View - ClinicalTrials.gov
Contrast sensitivity (ie, the ability to detect slight changes in luminance before they become indistinguishable) was assessed binocularly with distance manifest correction in place and uncorrected. Contrast sensitivity was assessed at spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd), where 3.0 cpd = A, 6.0 cpd = B, 12.0 cpd = C, and 18.0 cpd = D. Raw scores were log transformed. A higher numeric value represents better contrast sensitivity. Both eyes contributed to the analysis ...https://clinicaltrials.gov/ct2/show/NCT01941485?recr=Open&cond=%22Refractive+Errors%22&rank=11
Area summation in human vision at and above detection threshold | Proceedings of the Royal Society of London B: Biological...
Human performance was very well described here using equation (3.1). But how might this equation be expressed in the human brain? One possibility is that the elements of a spatial array of first-order mechanisms with contrast responses ∝C2.4 are summed by a higher-order contrast integrator that is suppressed by an overlapping spatial array of mechanisms with contrast responses ∝C2.0. Another possibility is that each element in the spatial array has contrast response ∝C2.4 and is inhibited by a signal pooled across the spatial array of mechanisms having responses ∝C2.0. This would produce first-order mechanisms with self-inhibition (Foley 1994), lateral inhibition (Snowden & Hammett 1998) and sigmoidal contrast responses (Legge & Foley 1980). Summing across the array would produce a higher-order contrast integrator consistent with equation (3.1). Furthermore, placing the limiting source of additive noise ...http://rspb.royalsocietypublishing.org/content/274/1627/2891
Suggestions for text color and font on grey background
Can anybody suggest some colors and simple fonts fot text (heading) on a grey background. Please check the image attached. Thank you!https://www.experts-exchange.com/questions/26641135/Suggestions-for-text-color-and-font-on-grey-background.html