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PubMed2003

Proposal of a quality-index or metric for soft copy display systems: contrast sensitivity study.

In addition to the inherent qualities of a digital image, the qualities of the monitor and graphics control card as well as the viewing conditions will affect the perceived quality of an image that is displayed on a soft copy display (SD) system. With the implementation of picture archiving and communication systems (PACS), many diagnoses are being made based on images displayed on SD devices, and consequently SD quality may affect the accuracy of diagnosis. Unlike the traditional film-on-lightbox display, optimal SD system parameters are not well defined, and many issues remain unsettled. In this article, the human observer performance, as measured by contrast sensitivity, for several SD devices including an active matrix liquid crystal flat panel monitor is reported. Contrast sensitivities were measured with various display system configurations. Experimental results showed that contrast sensitivity depends on many factors such as the type of monitor, the monitor brightness, and the gamma settings of the graphics card in a complex manner. However, there is a clear correlation between the measured contrast thresholds and the gradient of the display device's luminance response curve. Based on this correlation, it is proposed to use the gradient of luminance response curve as a quality-index or metric for SD devices.

Computer Terminals↗

PubMed1983

Reaching for rattles: a preliminary study of contrast sensitivity in 7-10 month old infants.

Contrast sensitivity for a 3 cycles deg-1 sinusoidal grating in 7-10 month old infants was tested by presenting gratings and uniform fields on cylinders, with the former providing auditory reinforcement when the infant picked them up. The method shows that a contrast as low as 7.5% can commonly be detected at this age, compared with 1-2% for adults under comparable conditions. However, as the development of hand preferences with the task as an indicator of visual sensitivity, it is concluded that this method is not in its present form suitable for vision testing on a wide scale or in a clinical setting.

Discrimination Learning↗

PubMed2001

Visual contrast sensitivity in deaf versus hearing populations: exploring the perceptual consequences of auditory deprivation and experience with a visual language.

Early deafness in humans provides a unique opportunity to examine the perceptual consequences of altered sensory experience. In particular, visual perception in the deaf may be altered as a result of their auditory deprivation and/or because the deaf rely heavily upon a visual language (American Sign Language, or ASL, in the US). Recently, we found that deaf, but not hearing, subjects exhibit a right visual field/left hemisphere advantage on a low-level direction of motion task, a finding that has been attributed to the deaf's experience with ASL [Psychol. Sci. 10 (1999) 256; Brain Res. 405 (1987) 268]. In order to determine whether this visual field asymmetry generalizes to other low-level visual functions, in this study we measured contrast sensitivity in deaf and hearing subjects to moving stimuli over a range of speeds (0.125-64 degrees /s). We hypothesized that if ASL use drives differences between hearing and deaf subjects, such differences may occur over a restricted range of speeds most commonly found in ASL. In addition, we tested a third group, hearing native signers who learned ASL early from their deaf parents, to further assess whether potential differences between groups results from ASL use. These experiments reveal no overall differences in contrast sensitivity, nor differences in visual field asymmetries, across subject groups at any speed tested. Thus, differences previously observed between deaf and hearing subjects for discriminating the direction of moving stimuli do not generalize to contrast sensitivity for moving stimuli, a result that has implications for the neural level at which plastic changes occur in the visual system of deaf subjects.

Adult↗

PubMed1989

Changes in colour contrast sensitivity associated with operating argon lasers.

A new test of colour vision using computer graphics has been used to obtain quantitative estimates of colour contrast sensitivity in ophthalmologists before and after they have treated patients by argon laser retinal photocoagulation. The colour vision of all subjects is normal when tested with the 100-hue test and HRR (Hardy, Rittler, Rand) plates, but colour contrast sensitivity measured along a tritan colour confusion line is selectively impaired after a treatment session. No such change occurs after a medical session spent examining patients with a fundus camera. In younger ophthalmologists the sensitivity recovers several hours after the treatment session ends, but in some persons there is a prolonged and possibly permanent elevation of threshold.

Adult↗

PubMed1996

Acuity and contrast sensitivity in monkeys after neonatal intraocular lens implantation with and without part-time occlusion of the fellow eye.

PURPOSE: The authors used a monkey model to evaluate intraocular lenses (IOLs) for the treatment of infantile cataract in humans. Specifically, they sought to assess the effectiveness of IOLs, with and without occlusion therapy, in preventing amblyopia. METHODS: A diffuser contact lens was placed on one eye each of 11 neonatal monkeys to simulate an infantile cataract. A unilateral lensectomy, combined with the implantation of an IOL, was performed on the same eye 1 to 2 weeks after birth. Clear contact lenses were used to adjust the optical correction of the pseudophakic eyes to a near point, and opaque lenses were used to maintain daily part-time (70%) occlusion of the fellow eyes of half the subjects. Behavioral methods were used to assess grating acuity, optotype acuity (Landolt C), and contrast sensitivity. RESULTS: In five of the animals, complications that developed in the eye with the implant were severe enough to interfere with visual function. The authors present only behavioral outcomes obtained before or in the absence of surgical complications. In monkeys that underwent daily 70% occlusion, grating acuity in the pseudophakic eyes eventually matured to normal adult levels. Grating acuity was significantly poorer in animals with no occlusion therapy. Even in animals with normal grating acuity, assessments of optotype acuity revealed amblyopic deficits; contrast sensitivity was impaired as well at middle and low spatial frequencies. CONCLUSIONS: The current study demonstrates that if there are no complications secondary to surgery, normal grating acuity can be obtained in neonatal monkey eyes that undergo IOL implantation, optical correction of the pseudophakic eye to a near point, and 70% occlusion of the fellow eye. However, these good outcomes for grating acuity cannot be attained without occlusion therapy. In addition, optotype acuity and sensitivity to contrast always are impaired.

Amblyopia↗

PubMed2006

Brain state and contrast sensitivity in the awake visual thalamus.

Neuronal responses to visual stimuli depend on both the nature of the stimulus and brain state. Here we examined the contrast sensitivity of visual thalamic neurons as awake rabbits shifted between alert and nonalert states. We found that despite a large increase in response gain with alertness, contrast sensitivity remained nearly constant. This accurate scaling might be achieved through a balanced increase in excitation and inhibition with alertness.

Action Potentials↗

PubMed1992

Electrophysiologically determined contrast sensitivity in patients with ocular hypertension and chronic glaucoma.

Subjectively assessed contrast sensitivity has been found to be abnormal in many patients with glaucoma. We previously reported the use of onset-offset visual evoked potential measurements to determine contrast threshold objectively. We now studied 216 patients (79 with ocular hypertension and 137 with chronic simple glaucoma) with this technique. In comparison with an age-matched control group (68 subjects), mean contrast threshold was found to be significantly different in both patient groups, the degree of significance being greater in the patients with chronic simple glaucoma. Additionally, the slope of the CI-CII amplitude versus log contrast plot was shown to be depressed in the majority of affected eyes in patients with unilateral chronic simple glaucoma. This measure appears to give an indication of suprathreshold contrast processing and is related to the difference in luminance between pattern elements, rather than the quality of the border or "edge" between them. The data support not only an increase in contrast threshold (reduced sensitivity) in early glaucoma and some patients with ocular hypertension but also a suppression in suprathreshold function that is not readily measurable with standard psychophysical methods. The findings are consistent with recent theories concerning the effect of early chronic simple glaucoma on the function of Y-type units of the M (magnocellular)-type pathways.

Aged↗

PubMed1999

[Contrast sensitivity in type I diabetics without symptoms of diabetic retinopathy].

UNLABELLED: The objective of the work was to assess whether in patients with IDDM without signs of diabetic retinopathy changes in the sensitivity function to contrast (CS) develop as compared with a group of healthy subjects matched for age but also as a result of the persistence of IDDM or the level of its long-term compensation investigated by means of glycated haemoglobin (HbA1c). CS was examined by the static method using a VCTS 6500 table from a distance of 208 and 420 cm which covered the spatial frequencies from 1.15 to 27.25 c/st. Moreover the authors assessed the best correctable central visual acuity on Snellen's optotypes, the ophthalmoscopic finding on the fundus with a colour photograph, fluorescein angiography and the HbA1c serum level. A group of 49 patients with IDDM was divided into two age groups: A(under 35 years), B (35 years and above). A marked decline of the CS function occurs in all spatial frequencies in both age groups. On comparison of the persistence of IDDM in group B no significant difference was found in CS, while in group A statistical significance was revealed in spatial frequencies 4 and 27.25 c/st. On comparison of the CS function in diabetics with a normal and pathological HbA1c level it was found that long-term hyperglycaemia has not a marked effect on visual functions. CONCLUSION: The decline of CS in patients with IDDM without signs of diabetic retinopathy is influenced in particular by the patient's age, in junior patients also by the persistence of IDDM. Examination of the CS is a simple non-invasive method suitable for screening of early affections of the eyes in IDDM.

Adult↗

PubMed2002

Improving the effectiveness of the infant contrast sensitivity card procedure.

Based on results from an earlier prototype, custom software and printing techniques were developed to construct a new card-based test of contrast sensitivity (CS) for nonverbal subjects. Compared with the prototype, the new CS card test contains three improvements: (1) larger, more salient test gratings; (2) higher contrast warm-up cards for each spatial frequency set; and (3) smaller contrast step size between adjacent cards. The success of the new cards was evaluated by testing 3.5- and 12-month-old human infants. Results indicated that the new version of the test required little time to complete (mean, 6.5 min) and provided accurate estimates of visual acuity. Also, group contrast sensitivity functions (CSFs) showed substantial development from 3.5 to 12 months of age. Surprisingly, however, group CSFs obtained with the new cards were lower than those obtained with the prototype, a discrepancy that may be due to differences in space average luminance between the two sets of cards. In all, the new CS card procedure possesses several merits that give it potential as an option for assessing spatial vision in infants, toddlers, and subjects with multiple impairments.

Contrast Sensitivity↗

PubMed1994

Age differences in spatial contrast sensitivity are not the result of changes in subjects' criteria or psychophysical performance.

PURPOSE: To analyze separately the sensory and nonsensory aspects of reductions in contrast sensitivity with age. METHODS: Two-alternative forced choice psychometric functions were fitted with a three-parameter Weibull function, which independently estimated threshold, slope, and upper asymptote of the functions. RESULTS: There were no changes in slope or upper asymptote with age, but contrast sensitivity decreased with age. CONCLUSIONS: Most studies of decreased visual function in the elderly are difficult to interpret because possible nonsensory effects are ignored. This paper illustrates a method that can be used to demonstrate a true sensory decline with age.

Adult↗

PubMed1989

Face processing, laterality and contrast sensitivity.

Two separate reaction time studies concerning person recognition were conducted with ex-servicemen who incurred unilateral brain injury during the Second World War. The first experiment investigated the ability to construct a facial representation and involved deciding whether a stimulus represented a face or a "non-face" made by repositioning the facial features into an unnatural configuration. Men with posterior right hemisphere (RH) lesions performed this task more slowly than those with left hemisphere (LH) damage and control subjects; the latter two groups did not differ. The second experiment was designed to tap the most basic level of overt person recognition: awareness of familiarity. When faces were used as stimuli, the RH injured group again showed increased response latencies compared with the other two groups. The reverse pattern, slower reaction times for the men with LH lesions with no difference between RH injured and control subjects, emerged when written names were employed. Spatial contrast sensitivity functions were measured in both studies and although both LH and RH injured men showed impaired contrast sensitivity, no hemispheric difference was apparent. Instead, a double dissociation of impairments of contrast sensitivity and face processing was evident.

Adult↗

PubMed1981

Contrast sensitivities through spectacles and soft contact lenses.

Contrast sensitivity function (CSF) measurements were made on nine subjects who wore a spectacle lens on one eye and a soft contact lens on the other eye continuously for 18 hr. The functions were the same for the two types of correction and did not become worse over time. Contrary to an earlier report by Applegate and Massof (1975), there was no evidence of a visual decrement caused by the wearing of soft contact lenses or from the moderately prolonged use of a contact lens. A major difference between our study and theirs was that none of our subjects had more than 0.12 D of astigmatism, whereas their soft contact lens subjects had from 0.75 to 1.00 D of astigmatism. Thus, impairments that were previously noted by soft lens wearers may be limited to astigmatic subjects. In addition, no evidence was found that occasional 18-hr use of soft contact lenses has any measurable, immediate effects on visual acuity as inferred from contrast thresholds.

Adolescent↗

PubMedDate not supplied

[Contrast sensitivity function. Results of an epidemiologic study].

The examination of contrast sensitive function partially tests the capabilities of ganglion cells. However, this method has not yet proven to be an unquestionable way of diagnosis, 108 Subjects with various pathological conditions were tested with this technique in order to confirm its value for ophthalmological pathology. The first epidemiological results show that there are changes in curves obtained for clinically sick patients, and that the currently used equipment is most sensitive of the 4 th frequency and high frequencies. Finally, each colored stimulation is very significant at low frequencies.

Contrast Sensitivity↗

PubMed1983

Why do we measure contrast sensitivity?

The fundamental advantage of measuring the contrast sensitivity of the eye using sinusoidal gratings is that it gives a more complete description of its functional range. Such measurements increase our understanding of how we perceive events in the visual world. The technique can also be applied to other animals whose visual system is matched to a different visual environment. Moreover, single neurones can be measured and compared with psychophysical results. In recent years it has also become possible to investigate abnormal vision using clinical material.

Amblyopia↗

PubMed1978

An investigation into the variation of human contrast sensitivity with age and ocular pathology.

The contrast sensitivities to sine-wave grating stimuli were measured for 36 observers with ages in the range 8 to 67 years. Thirty-one observers had normal, healthy vision while 4 were suffering from diabetic retinopathy and 1 had a early lens opacities and macular degeneration. The younger members of the group with normal vision were less sensitive to low spatial frequencies and the older members were less sensitive to high spatial frequencies than the middle-aged observers. The 5 observers with pathological conditions were less sensitive to most grating stimuli than those with normal vision.

Adolescent↗

PubMed1986

[Clinical value of the colored contrast sensitivity test. Preliminary note].

Evaluation of color contrast sensitivity is a new test for the assessment of visual capacity and especially of light stimulation transfer along the optic pathway. The color technique yields more accurate results. It is combined with previously existing functional examinations and allows very early detection of subclinical signs of starting pathological processes.

Color Perception Tests↗

PubMed1983

Temporal contrast sensitivity in optic neuritis and amblyopia.

Temporal contrast sensitivity was measured in patients with optic neuritis and anisometropic amblyopia. In optic neuritis, attenuated sensitivity was detected at all frequency ranges; however, its degree was more severe than that of retinal diseases even when visual acuity was the same. At the convalescent stage, the low-frequency sensitivity was restored first, and high-frequency loss was observed even when the visual acuity was restored to 1.0. Two amblyopic patients showed attenuated sensitivity at high- and intermediate-frequency ranges, and in one case all frequency sensitivity attenuated. Three other patients showed normal sensitivity. By occlusion of the nonamblyopic eye, recovery of sensitivity was observed in one patient, whose visual acuity improved.

Adolescent↗

PubMed1978

Normal and amblyopic contrast sensitivity function in central and peripheral retinas.

Contrast sensitivity functions (CSF's) for temporally modulated sine wave gratings were established at a variety of retinal eccentricities in three esotropic amblyopes with acuities in their amblyopic eyes of 20/50, 20/100, and 20/300. CSF's were shown to vary with eccentricity and the degree of amblyopia. In the 20/50 amblyope, reduced CSF's were confined to the higher spatial frequencies and to the central 5 degrees of the retina. Given greater acuity deficits (e.g., 20/100 and 20/300), CSF's were depressed over the entire spatial frequency range tested, with the effects intruding farther into the peripheral retina than for the 20/50 amblyope. In addition, the detection of the temporal as well as the spatial modulation was depressed in the CSF's of the observers with severe amblyopia.

Adult↗