Showing papers on "Contrast (vision) published in 2000"
TL;DR: This study shows why bubble volume is a much better indicator of SonoVue™’s efficacy than is bubble count, under which size bubbles do not contribute appreciably to the echogenicity at medical ultrasound frequencies.
Abstract: Gorce J-M, Arditi M, Schneider M. Influence of bubble size distribution on the echogenicity of ultrasound contrast agents: A study of SonoVue™. Invest Radiol 2000;35:661–671.RATIONALE AND OBJECTIVES.To study the relative contributions of different bubble size classes to SonoVue™’s echogenicity in fu
416 citations
Journal Article•
TL;DR: In this article, the authors examined the optical and visual impact of tear break-up on the fundus image and measured the psychophysical contrast sensitivity and the spatial distribution of tear thickness changes by retroillumination.
Abstract: Purpose The purpose of this study was to examine the optical and visual impact of tear break-up. Methods Optical quality of the eye was assessed during periods of nonblinking by quantifying vessel contrast in the fundus image and by monitoring the psychophysical contrast sensitivity and the spatial distribution of tear thickness changes by retroillumination. All measures were obtained from three eyes either with or without a soft contact lens. Results A noticeable decrease in retinal vessel contrast and contrast sensitivity were observed soon after a blink. Both of these measures of optical quality of the eye showed a similar pattern of image degradation both with and without a soft contact lens. Although trial-to-trial variability was considerable, sample means show that image contrast in the low spatial frequency range can drop to between 20% and 40% of initial values after 60 seconds of nonblinking. Retroillumination of the tear film showed local intensity fluctuations that progressively spread across the pupil with increasing time after the blink. Conclusions Optical aberrations created by tear break-up contribute to the decline in image quality observed objectively and psychophysically. The decline in image quality that accompanies tear break-up may be a direct cause of the blurry vision complaints commonly encountered in dry-eye patients.
278 citations
TL;DR: Differences between real and simulated saccades in the magnitude and time course of sensitivity loss suggest that saccadic suppression has an extraretinal component.
Abstract: We measured the time course of saccadic suppression and tested whether suppression results entirely from retinal image motion or has an extraretinal source. We measured contrast thresholds for low-frequency gratings modulated either in luminance, at 17 cd/m 2 and 0.17 cd/m 2 , or color at 17 cd/m 2 . Gratings were flashed on a uniform background before, during, or after voluntary 12° saccades and, additionally in the case of luminance modulated gratings, saccades simulated by mirror motion. A 10-fold decrease in contrast sensitivity was found for luminance-modulated gratings with saccades, but little suppression was found with simulated saccades. Adding high-contrast noise to the display increased the magnitude and the duration of the suppression during simulated saccades but had little effect on suppression produced by real saccades. Suppression anticipates saccades by 50 msec, is maximal at the moment of saccadic onset, and outlasts saccades by ∼50 msec. At lower luminance, suppression is reduced, and its course is shallower than at higher luminance. Simulated saccades produce shallower suppression over a longer time course at both luminances. No suppression was found for chromatically modulated gratings. Differences between real and simulated saccades in the magnitude and time course of sensitivity loss suggest that saccadic suppression has an extraretinal component. We model the effects of saccades by adding a signal to the visual input, so as to saturate the nonlinear stage of visual processing and make detection of a test stimulus more difficult.
273 citations
Patent•
01 Dec 2000TL;DR: In this article, an image recognition system recognizes correspondence between object images contained respectively in two images obtained by two infrared ray cameras by using a correlation parameter indicative of a correlation between a reference pattern contained in the reference image and containing an object image and each pattern containing in the comparison image and identical in shape to the reference pattern.
Abstract: An image recognition system recognizes correspondence between object images contained respectively in two images obtained by two infrared ray cameras. One of the two images is set to a reference image and another of the two images to a comparison image. A correlation parameter indicative of a correlation between a reference pattern contained in the reference image and containing an object image and each pattern contained in the comparison image and identical in shape to the reference pattern is calculated by using a luminance value indicative of a luminance of the reference pattern and a luminance value indicative of a luminance of the each pattern contained in the comparison image. Based on the calculated correlation parameter, a pattern having a highest correlation with the reference pattern is extracted from the comparison image as a corresponding pattern which corresponds to the reference pattern. Identity between the object image contained in the reference pattern and the object image contained in the corresponding pattern is determined based on a difference between a contrast value indicative of a contrast of the reference pattern and a contrast value indicative of a contrast of the corresponding pattern.
258 citations
TL;DR: Investigating how these regions are modulated by two common variables in reading found that increasing word length increases the demands on both local feature and global shape processing, but increasing visual contrast increases the demanding on local feature processing while decreasing the demand on global shapeprocessing.
Abstract: Previous studies have shown differential responses in the fusiform and lingual gyri during reading and suggested that the former is engaged in processing local features of visual stimuli and the latter is engaged in global shape processing. We used positron emission tomography in order to investigate how these regions are modulated by two common variables in reading: word length (three, six and nine letters) and perceptive similarity to the background (high and low contrast). Increasing both word length and visual contrast had a positive monotonic effect on activation in the bilateral fusiform. However, in the lingual gyrus, activation increased with increasing word length but decreased with increasing contrast. On the basis of previous studies, we suggest that (i) increasing word length increases the demands on both local feature and global shape processing, but (ii) increasing visual contrast increases the demands on local feature processing while decreasing the demands on global shape processing.
234 citations
TL;DR: A novel technique for manipulating contrast in projection reconstruction MRI is described, implemented into a fast spin‐echo (FSE) sequence, and it is shown that multiple T2‐weighted images can be reconstructed from a single image data set.
Abstract: A novel technique for manipulating contrast in projection reconstruction MRI is described. The method takes advantage of the fact that the central region of k-space is oversampled, allowing one to choose different filters to enhance or reduce the amount that each view contributes to the central region, which dominates image contrast. The technique is implemented into a fast spin-echo (FSE) sequence, and it is shown that multiple T2-weighted images can be reconstructed from a single image data set. These images are shown to be nearly identical to those acquired with the Cartesian-sampled FSE sequence at different effective echo times. Further, it is demonstrated that T2 maps can be generated from a single image data set. This technique also has the potential to be useful in dynamic contrast enhancement studies, capable of yielding a series of images at a significantly higher effective temporal resolution than what is currently possible with other methods, without sacrificing spatial resolution. Magn Reson Med 44:825–832, 2000. © 2000 Wiley-Liss, Inc.
164 citations
TL;DR: It was demonstrated that reading index is valuable in predicting the ability to perform daily living tasks and therefore may be useful in the visual assessment of the visually impaired individual.
Abstract: AIMS—To examine the relation between measures of vision and ability to perform daily living tasks in those visually impaired with macular degeneration.
METHODS—A visual functioning index (daily living tasks dependent on vision: DLTV) was used to evaluate patients' perception of their ability to perform vision dependent tasks. Distance visual acuity, near visual acuity, reading speed, and contrast sensitivity were measured in all patients. In addition, a new measure of reading ability was derived, designated the reading index. This takes into account both the size of the text read and the time to read it and is equivalent to the reading speed in words per minute divided by text size in M.
RESULTS—The reading index was found to show best associations with the majority of items within the DLTV. Stepwise regression identified the combination of reading index and distance visual acuity as having the best associations with DLTV items. The present study also demonstrated that specific levels of vision as measured by acuity, reading index, and contrast sensitivity corresponded with different perceived amounts of difficulty in the performance of daily living tasks.
CONCLUSIONS—This study showed that reading index is valuable in predicting the ability to perform daily living tasks and therefore may be useful in the visual assessment of the visually impaired individual. In addition, this study identified specific levels of vision at which individuals reported different degrees of difficulty in performing daily living tasks.
157 citations
TL;DR: Major and independent impairment of both color and contrast discrimination in PD patients is documented, such as the frequency of falls or visual hallucinations.
151 citations
TL;DR: Low-Contrast Sloan Letter Chart testing is a highly reliable method of visual assessment, and provides information on an aspect of neurologic impairment in MS which is not captured by Snellen visual acuity or ambulation status.
Abstract: The quantitative assessment of visual function in multiple sclerosis (MS) clinical trials has been limited to Snellen visual acuity. The purpose of this study was to examine the inter-rater reliability and test characteristics of a new visual outcome measure, the Low-Contrast Sloan Letter Charts, in patients with MS and visually-asymptomatic volunteers. Contrast letter acuity scores (letter scores) were measured at each of four contrast levels (100, 5, 1.25 and 0.6%) by two independent raters. Inter-rater agreement was described with the intraclass correlation coefficient (ICC) and comparison of mean scores. Excellent inter-rater agreement (ICC=0.86 - 0.95) was demonstrated at each contrast level among MS patients (n=100) and visually-asymptomatic volunteers (n=33). Average letter scores at the lowest contrast level (0.6%) were highly variable in the MS group, even among patients with visual acuities of 20/20 or better, and among those who required no assistance for ambulation. Low-Contrast Sloan Letter Chart testing is a highly reliable method of visual assessment, and provides information on an aspect of neurologic impairment in MS which is not captured by Snellen visual acuity or ambulation status. This new method demonstrates excellent potential as a visual function outcome measure for future MS clinical trials.
146 citations
TL;DR: It is concluded that cortical mechanisms of contrast gain control for pattern stimuli of relatively low temporal frequency and high luminance contrast are lacking or severely impaired in photosensitive subjects.
Abstract: Television and video games may be powerful triggers for visually induced epileptic seizures. To better understand the triggering elements of visual stimuli and cortical mechanisms of hyperexcitability, we examined eleven patients with idiopathic photosensitive epilepsy by recording visually evoked potentials (VEPs) in response to temporally modulated patterns of different contrast. For stimuli of low–medium, but not high, temporal frequency, the contrast dependence of VEP amplitude and latency is remarkably abnormal for luminance contrast (black–white), but not so for chromatic contrast (equiluminant red–green) stimuli. We conclude that cortical mechanisms of contrast gain control for pattern stimuli of relatively low temporal frequency and high luminance contrast are lacking or severely impaired in photosensitive subjects.
143 citations
TL;DR: Fits of the ModelFest data with five models are reported: Peak Contrast, Contrast Energy, Generalized Energy, a Gabor Channels model, and a Discrete Cosine Transform model.
Abstract: The ModelFest Phase One dataset is a collection of luminance contrast thresholds for 43 two-dimensional monochromatic spatial patterns confined to an area of approximately two by two degrees. These data were collected by a collaboration among twelve laboratories, and were designed to provide a common database for calibration and testing of spatial vision models. Here I report fits of the ModelFest data with five models: Peak Contrast, Contrast Energy, Generalized Energy, a Gabor Channels model, and a Discrete Cosine Transform model. The Gabor Channels model provides the best fit, though the other, simpler models, with the exception of Peak Contrast, provide remarkably good fits as well. Though there are clear individual differences, regularities in the data suggest the possibility of constructing a standard observer for spatial vision.
TL;DR: The results suggest that specific changes in the cognitive/behavioral state of a subject can exert selective and reliable modulations of cortical activity in early visual cortex, even in V1, and that visual areas and pathways that are highly sensitive to small changes in a given stimulus feature are selectively modulated during discrimination judgments on that feature.
Abstract: We performed a series of experiments to quantify the effects of task performance on cortical activity in early visual areas. Functional magnetic resonance imaging (fMRI) was used to measure cortical activity in several cortical visual areas including primary visual cortex (V1) and the MT complex (MT+) as subjects performed a variety of threshold-level visual psychophysical tasks. Performing speed, direction, and contrast discrimination tasks produced strong modulations of cortical activity. For example, one experiment tested for selective modulations of MT+ activity as subjects alternated between performing contrast and speed discrimination tasks. MT+ responses modulated in phase with the periods of time during which subjects performed the speed discrimination task; that is, MT+ activity was higher during speed discrimination than during contrast discrimination. Task-related modulations were consistent across repeated measurements in each subject; however, significant individual differences were observed between subjects. Together, the results suggest 1) that specific changes in the cognitive/behavioral state of a subject can exert selective and reliable modulations of cortical activity in early visual cortex, even in V1; 2) that there are significant individual differences in these modulations; and 3) that visual areas and pathways that are highly sensitive to small changes in a given stimulus feature (such as contrast or speed) are selectively modulated during discrimination judgments on that feature. Increasing the gain of the relevant neuronal signals in this way may improve their signal-to-noise to help optimize task performance.
TL;DR: In this paper, the authors developed a systematic procedure for the assessment of three visual thresholds (detection, recognition, and visual impact) through controlled slide-viewing tests using computer simulated images with modified visual attributes.
01 Jan 2000
TL;DR: This method is based on the underlying physics of the degradation and the parameters required for enhancement are estimated from the image itself, and significant improvements in terms of contrast, visible range and color fidelity are evident when compared to existing methods.
Abstract: Degradation of images by the atmosphere often restricts imaging applications to good visibility conditions. For example, when imaging the terrain from a forward-looking airborne camera, the atmospheric degradation causes both a loss in contrast and color information. Enhancement of such images is a difficult task due to the complexity in restoring both the luminance and chrominance while maintaining good color fidelity. One particular problem is the fact that the level of contrast loss depends strongly on the wavelength; shorter wavelengths i.e., blue are more effected. In this paper, a novel method is presented for the enhancement of color images. This method is based on the underlying physics of the degradation and the parameters required for enhancement are estimated from the image itself. The proposed method is tested using synthetic images to explore the limitations and reliability of the method under different visibility conditions. Enhancement is performed on real images taken using an airborne camera at a height of approximately 1000 meters in hazy conditions for which the visibility is approximately 10 kilometers. Significant improvements in terms of contrast, visible range and color fidelity are evident when compared to existing methods.
TL;DR: The limits imposed by the optical and neural design of the eye are explored, allowing for high contrast visual acuity between 20/8 and 20/10 and correcting the higher order aberrations will provide images with higher contrast and crisper edges.
Abstract: Non-invasive wavefront sensing of the human eye provides the necessary information to design corrections which minimize the monochromatic optical errors of the eye beyond simple sphere (defocus) and cylinder (astigmatism). These "ideal" corrections must move with the eye, maintaining proper alignment with the eye's optics. Viable modes of correction include contact lenses, refractive surgery and intraocular lenses. Will these "ideal" corrections lead to better vision? If so, how much better? Here we explore the limits imposed by the optical and neural design of the eye. For larger pupil sizes (>3 mm diameter) "ideal" corrections improve the optical quality of the retinal image beyond the limits imposed by photoreceptor spacing. Photoreceptor spacing limits visual acuity to between 20/8 and 20/10. Correcting the higher order aberrations will provide images with higher contrast and crisper edges. When perfected, "ideal" corrections will provide for high contrast visual acuity between 20/8 and 20/10.
TL;DR: An abnormal pattern of long-range connectivity between spatial filters or a loss of such connectivity appears to be the primary source of contour integration deficits in amblyopia and strabismus.
TL;DR: The detriment in color vision caused by yellow-colored lenses enhances contrast when viewing bright objects against a blue-based background, such as the sky.
Abstract: PURPOSE: Although many studies have shown a subjective preference for yellow lenses, there has been little success in determining the clinical nature of this benefit. METHOD: Contrast sensitivity, color vision, accommodative-convergence, and visual acuity were measured in a group of 20 young subjects along with subjective rating of their perception through clear control lenses (380-nm cut-off), yellow lenses (450-nm cut-off), dark yellow lenses (511-nm cut-off), and orange lenses (527-nm cut-off). RESULTS: A systematic detriment to color vision was found to occur with increasing cut-off wavelength of the yellow lenses (p < 0.001) and this was significantly correlated to subjective ratings of color (r = -0.66) and brightness (r = -0.34). Perceived brightness significantly improved for the yellow (450-nm cut-off) lens only (p < 0.001). Although tinted lenses reduced contrast sensitivity to a white on black grating, there was a significant improvement in low to midrange spatial frequencies when measured using a white-on-blue grating. CONCLUSIONS: The detriment in color vision caused by yellow-colored lenses enhances contrast when viewing bright objects against a blue-based background, such as the sky. Contrast of overlying objects is enhanced is due to the selective reduction of short-wavelength light by the yellow lenses.
01 Jan 2000
TL;DR: In this article, the authors demonstrate that motion in depth can be seen based solely on inter-ocular velocity differences using binocularly uncorrelated random-dot kinematograms.
Abstract: Two different binocular cues are known for detecting motion in depth. One is disparity change in time and the other is inter-ocular velocity difference. In contrast to the well known fact of the use of the disparity cues, no evidence of contribution of inter-ocular velocity differences for detecting motion in depth has been reported. We demonstrate that motion in depth can be seen based solely on inter-ocular velocity differences using binocularly uncorrelated random-dot kinematograms. This indicates that the visual system uses monocular velocity signals for processing motion in depth in addition to disparity change in time. © 2000 Elsevier Science Ltd. All rights reserved.
TL;DR: It is shown that sensitivity to the envelope varies in proportion to the spatial frequency of the carrier, and that orientationally and spatially-band pass filtering precedes the detection of second-order structure.
TL;DR: In this article, the effects of polarity and luminance contrast on visual performance and display quality were investigated by measuring the subjects' performance on a discriminating VDT task and using the subjective evaluation of subjects.
TL;DR: It is concluded that selectivity for the orientation of kinetically defined boundaries first emerges in area V2 rather than in primary visual cortex, and that while responses to luminance edges or local motion are indigenous to V2, KE-selective responses may involve feedback entering the ventral stream at a point downstream with respect to V1.
Abstract: We recorded responses in 107 cells in the primary visual area V1 and 113 cells in the extrastriate visual area V2 while presenting a kinetically defined edge or a luminance contrast edge. Cells mee...
TL;DR: Comparing the performance of the red-green, blue-yellow and luminance postreceptoral mechanisms on a contour integration task requiring the linking of oriented Gabor elements across space to extract a winding 'path' or contour suggests that the common integration process remains sensitive to the color contrast and phase of its inputs.
TL;DR: In this paper, the effect of Levodopa in improving visual function in patients treated within 45 days of onset of nonarteritic anterior ischemic optic neuropathy (NAION) was studied.
TL;DR: To investigate the effect of defocus on contrast sensitivity as a function of age in healthy subjects, the through focus contrast sensitivity was measured in 100 healthy subjects aged 20–69.
TL;DR: Output images taken from the models indicate that natural images do contain useful second-order structure and reveal variations in texture and features defined by such variations, suggesting that the two types of image ‘content’ may be statistically independent.
Abstract: The human visual system is sensitive to both first-order variations in luminance and second-order variations in local contrast and texture. Although there is some debate about the nature of second-order vision and its relationship to first-order processing, there is now a body of results showing that they are processed separately. However, the amount, and nature, of second-order structure present in the natural environment is unclear. This is an important question because, if natural scenes contain little second-order structure in addition to first-order signals, the notion of a separate second-order system would lack ecological validity. Two models of second-order vision were applied to a number of well-calibrated natural images. Both models consisted of a first stage of oriented spatial filters followed by a rectifying nonlinearity and then a second set of filters. The models differed in terms of the connectivity between first-stage and second-stage filters. Output images taken from the models indicate that natural images do contain useful second-order structure. Specifically, the models reveal variations in texture and features defined by such variations. Areas of high contrast (but not necessarily high luminance) are also highlighted by the models. Second-order structure--as revealed by the models--did not correlate with the first-order profile of the images, suggesting that the two types of image 'content' may be statistically independent.
TL;DR: To what extent measurement of standard visual acuity allows prediction of other spatial vision measures on an individual basis when high correlations exist betweenvisual acuity and the other measures is examined.
Abstract: :PurposeTo examine to what extent measurement of standard visual acuity allows prediction of other spatial vision measures on an individual basis when high correlations exist between visual acuity and the other measures.MethodsA series of spatial vision functions were measured in a sample of
TL;DR: Comparison thresholds for 1 c/deg Gabor patterns (targets) were measured as a function of the contrast of Gabor pedestal patterns (TvC functions), where the pedestals paired with each target were modulated in a wide range of directions in color space.
TL;DR: In this article, a correlation analysis was applied to human spatial frequency contrast sensitivity and adults showed power law correlational structure consistent with a β of 1.09-1.20 (closely matched to that of natural images).
TL;DR: Examination of associations between eye disease and tests of visual function with self‐reported visual disability in patients with confirmed or suspected eye disease finds no clear relationship between disease and test results.
Abstract: Purpose: To examine associations between eye disease and tests of visual function with self-reported visual disability.
Methods: The Blue Mountains Eye Study is a cross-sectional census-based survey of eye disease in two postcode areas in the Blue Mountains, west of Sydney, Australia. Of 4433 eligible residents, 3654 (82.4%) participated. Subjects had a detailed eye examination, including tests of visual acuity, contrast sensitivity, disability glare and visual field. Lens and retinal photographs were taken and graded according to standardized protocols for presence of cataract, early and late age-related maculopathy, glaucoma, diabetic retinopathy, retinal vein occlusion and other eye diseases. An interviewer-administered questionnaire included questions about perception of visual disability.
Results: Scores on all tests of visual function significantly decreased with age (P < 0.0001). This decrease persisted for all tests except disability glare after excluding subjects with identifiable eye disease. The presence of one or more eye diseases was significantly associated with all (self-reported) measures of visual disability (trouble driving at night, difficulty recognizing a friend across the street, reading a newspaper or recognizing detail on television); mixed cataract (cortical and nuclear, or posterior subcapsular and nuclear) was associated with trouble driving at night and difficulty recognizing a friend across the street. A 10-letter (two-line) decrease in best corrected or presenting visual acuity was significantly associated with all self-reported measures of visual disability, as was a two-step decrease in contrast sensitivity. A five-point increase in points missing in the visual field was weakly but significantly associated with all self-reported measures of visual disability except trouble driving at night.
Conclusions: Visual function declines with age. Impaired visual function was strongly, and eye disease relatively weakly associated with reports of visual disability.
TL;DR: It is found that under poorly attended conditions targets can be detected only when the target contrast exceeds the surround contrast (contrast popout) or when thetarget orientation differs from the surround orientation by more than 10-15 degrees (orientation popout).