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Results for “Contrast Sensitivity”

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At least 19 recordsLinked to original sources

PubMed1990

The influence of stimulus length on the oblique effect of contrast sensitivity.

Contrast sensitivity for grating of different orientations was measured at various stimulus lengths. The oblique effect of contrast sensitivity was observed to increase in magnitude as the length of the truncated gratings was increased from 0.5 to 5.6 deg. This finding refutes a purported distinction between the contrast sensitivity oblique effect and the orientation discrimination oblique effect. Thus, these results are consistent with the idea that the contrast sensitivity oblique effect and the orientation discrimination oblique effect share the same common underlying anisotropic basis. These results also show that grating summation differs at oblique and nonoblique orientations in terms of length summation as well as in terms of width summation.

Adult↗

PubMed1982

Subtle disturbances of vision with compressive lesions of the anterior visual pathway measured by contrast sensitivity.

Contrast thresholds were determined for patients with compressive lesions of the chiasm or optic nerve but whose visual acuity was 20/20 on the Snellen scale. A generalized loss of contrast sensitivity for spatial frequencies ranging from 0.2 to 6.4 cycles per degree was found even in patients with normal color vision and full visual fields. After surgery was performed, improvements in the fields and color vision were seen in those patients who also showed a significant increase in their postoperative contrast sensitivity scores. Contrast sensitivity is shown to be a useful procedure for evaluating very mild visual complaints as well as for establishing early diagnosis and evaluation of surgical therapy in patients with compressive lesions of the anterior visual pathway.

Adult↗

PubMed1994

Spatiotemporal separability in contrast sensitivity.

Contrast sensitivity functions were measured in two ways: by counterphase modulation; and by in-phase modulation, in which the luminance of every point of a spatial grating was sinusoidally modulated in phase with one another. Contrast sensitivity functions measured by counterphase modulated gratings show spatiotemporal interactions that represent bandpass filtering. Contrast sensitivity functions measured by in-phase modulation are even more sharply bandpass in the spatial frequency domain, but they are spatiotemporally decoupled, i.e. the effects of spatial and temporal variables are separable. This difference can be explained by the composition of the frequency components of the counterphase and the in-phase modulated gratings and by masking between components. The results suggest that the intrinsic filters are low-pass exponentials, that they are spatiotemporally separable, and that the spatiotemporal interaction of counterphase gratings is best described as masking by the zero spatiotemporal frequency component of the test gratings.

Contrast Sensitivity↗

PubMed1988

Operation Everest II: lack of an effect of extreme altitude on visual contrast sensitivity.

Contrast sensitivity thresholds were studied over 40 d during gradual ascent to a simulated terrestrial altitude of 25,000 ft in a decompression chamber. Only ambient pressure, and thus inspired oxygen pressure, was varied, thereby eliminating many of the confounding effects of cold, dehydration, malnutrition and exhaustion, inevitably encountered on very high mountains. Contrast sensitivity thresholds measured by the Ginsburg Vistech test showed no overall impairment as altitude increased. These results are different from those of other previously reported vision studies involving shorter exposures, lower altitudes, and lower test luminances. However, our results can be explained on the basis of the higher stimulus luminances used in our contrast sensitivity testing. Compared to the luminance levels involved in previously reported testing, our higher luminance stimuli would be less likely to be affected by hypoxia.

Adult↗

PubMed1988

Age differences in Vistech near contrast sensitivity.

Contrast sensitivity was measured at near using the Vistech 6000 Contrast Test System (VCTS) in 287 persons aged 4 to 87 years. Obtained data compared well with those previously reported for the Vistech charts. Results indicate an age-related loss in sensitivity to intermediate and higher spatial frequencies. This is consistent with the age trends observed using other methods for measuring contrast sensitivity functions (CSFs). However, the Vistech charts yield contrast sensitivity values which are lower than those obtained previously with the Nicolet system. These between-method differences are greatest at lower spatial frequencies, and are attributed to the small number of grating cycles in the Vistech charts. The data are used to develop provisional age norms for the Vistech charts which allow the assessment of an individual's performance relative to their age cohort. Recommendations for use and future development of the Vistech charts are also given.

Adolescent↗

PubMed1997

Effects of optical correction media on contrast sensitivity.

Contrast sensitivity functions (CSFs) were obtained for 257 emmetropic subjects (514 eyes) and 35 contact lens users (64 eyes) in the Republic of Singapore Air Force using the Vistech Contrast Test System. For the emmetropes, contrast sensitivity tests were carried out with and without plano spectacles (PS). For the myopes, we compared their performances with spectacles, daily-wear soft contact lenses (CLs), and CL plus PS at Snellen visual acuities of 6/6 or better. Paired t-tests showed that there were no significant differences (P > 0.05) when CSFs of the emmetropes were measured with and without PS and when that of the CL users were measured with spectacles, CL and CL plus PS. We therefore conclude that myopic optical correction media do not retard CSF significantly based on the Vistech charts, although they may reduce image size and modify light transmission by being imperfect transparencies. The observed decrease in CSF for myopes even after myopic correction might therefore be related to other factors associated with myopia, such as retinal changes or possibly mild amblyopia.

Contact Lenses↗

PubMed2006

The effect of spatial configuration on surround suppression of contrast sensitivity.

Contrast sensitivity is known to be strongly influenced by the target surround, yet the role of the surround interaction in visual processing remains unclear. Previously, we have shown that the surround strongly suppresses contrast sensitivity in the periphery when the surround spatial frequency and orientation match those of the target (Petrov, Carandini, & McKee, 2005). Here, we explore how various spatial characteristics of the iso-oriented and frequency-matched surround, such as surround phase and spatial layout, affect suppression. We manipulated surround geometry (annulus ring, half annulus, and bow tie) and its separation from the target (both laterally and in depth) and varied the position of the half-annulus and bow-tie surrounds with respect to Gabor target's orientation and with respect to its location in the visual field (i.e., radial vs. tangential surrounds). We also compared monoptic, dichoptic, and binocular surround suppression. Except for a significant radial-tangential anisotropy, only the area of the surround and the lateral separation between the surround and target had a significant effect on the magnitude of suppression. We showed that, although suppression amplitude remains constant with stimulus eccentricity, the lateral extent of suppression scales in proportion to the eccentricity. The most surprising finding was that the extent of surround suppression does not scale with stimulus size or spatial frequency. We suggest that the properties of surround suppression are best explained by a mechanism that selects salient targets for subsequent saccades.

Contrast Sensitivity↗

PubMed1988

Aging and luminance-adaptation effects on spatial contrast sensitivity.

Contrast sensitivity as a function of target luminance for four spatial frequencies (0.5, 2, 4, and 8 cycles/deg) was measured in younger (n = 12; age range, 19-35 years) and older (n = 11; age range, 68-79 years) adults in order to examine the feasibility of optical and neural explanations for the impairment of contrast sensitivity in older adults. All subjects were free from identifiable ocular disease and had good acuity. Sensitivity for each spatial frequency was measured at eight luminance levels spanning 3.5 log units in the photopic-mesopic range. When gratings were flickered at 0.5 Hz, functions for older adults were displaced downward on the sensitivity axis across all luminance levels, and the slopes of these functions were steeper than those for younger adults, suggesting that optical mechanisms alone cannot account for the vision loss in older adults. Further measurements, in which spatial targets were flickered at 7.5 Hz, indicated that this faster temporal modulation affected sensitivity as a function of luminance differentially in younger and older adults. These data imply that the neural mechanisms subserving human spatial vision undergo significant changes during adulthood.

Adaptation, Physiological↗

PubMed1980

Spatial vision and aging. I: Contrast sensitivity.

Contrast sensitivity functions (CSFs) were measured for two groups of healthy observers, a younger group with mean age 18.5 years and an older group with mean age 73 years. Although the two groups had virtually identical sensitivities to high spatial frequencies (gratings with narrow bars), the younger observers were three times more sensitive at low and intermediate spatial frequencies (gratings with wider bars) than were the older observers. Groups did not differ in relative sensitivity to gratings flickered at two rates, .33 and 6 Hz. The reduced sensitivity of older observers to low spatial frequencies cannot be explained in terms of optical factors or as the result of ocular pathology; it probably reflects a loss in that visual sub-system responsible for detecting low spatial frequency, temporally transient targets.

Adolescent↗

PubMed2000

What covariance mechanisms underlie green/red equiluminance, luminance contrast sensitivity and chromatic (green/red) contrast sensitivity?

In order to investigate the mechanisms underlying green/red equiluminance matches in human observers and their relationship to mechanisms subserving luminance and/or chromatic (green/red) contrast sensitivity, we tested 21 human subjects along these dimensions at 16 different spatial and temporal frequencies (spatial frequency, 0.25-2 c/deg; temporal frequency, 2-16 Hz) and applied factor analysis to extract mechanisms underlying the data set. The results from our factor analysis revealed separate sources of variability for green/red equiluminance, luminance sensitivity and chromatic sensitivity, thus suggesting separate mechanisms underlying each of the three main conditions. When factor analysis was applied separately to green/red equiluminance data, two temporally-tuned factors were revealed (factor 1, 2-4 Hz; factor 2, 8-16 Hz), suggesting the existence of separate mechanisms underlying equiluminance settings at low versus high temporal frequencies. In addition, although the three main conditions remained separate in our factor analysis of the entire data set, our correlation matrix nonetheless revealed systematic correlations between equiluminance settings and luminance sensitivity at high temporal frequencies, and between equiluminance settings and chromatic sensitivity at low temporal frequencies. Taken together, these data suggest that the high temporal frequency factor underlying green/red equiluminance is governed predominantly by luminance mechanisms, while the low temporal frequency factor receives contribution from chromatic mechanisms.

Color Perception↗

PubMed1991

Assessment of potential contrast sensitivity. Part I: Preoperative prediction of contrast sensitivity following intraocular lens implantation.

Preoperative contrast sensitivity functions (CSFs) were determined for 15 cataract patients using laser-generated patterns that effectively bypassed the optical components of the eye. These functions were compared with postoperative CSFs determined using traditional methods by transmission through the optics of the eye. Accurate prediction of postoperative contrast sensitivity occurred in 91% of the cases (ten of 11) for patients with preoperative visual acuity of 20/200 or better and in 67% of all the cases (ten of 15). Prediction failures occurred when the laser interferometer was not able to penetrate the cataract or when postoperative complications occurred. These results suggest that preoperative measurement of laser interferometric CSF is a useful predictor of postoperative CSF for patients with mild to moderate cataracts that can be bypassed by the laser and with better than 20/200 preoperative visual acuity. The problem of assessment when lens opacity is advanced is addressed in Part II.

Aged↗

PubMed2003

Contrast sensitivity.

Spatial contrast is a physical dimension referring to the light-dark transition of a border or an edge in an image that delineates the existence of a pattern or an object. Contrast sensitivity refers to a measure of how much contrast a person requires to see a target. Contrast-sensitivity measurements differ from acuity measurements; acuity is a measure of the spatial-resolving ability of the visual system under conditions of very high contrast, whereas contrast sensitivity is a measure of the threshold contrast fur seeing a target. Today the most common methods for measuring contrast sensitivity are chart-based systems that can be mounted on the wall. These charts use test targets that are either sine-wave gratings or letters. Which specific chart a clinician selects should be guided by his or her purpose in using contrast sensitivity for patient management. In the research setting, chart selection should rest on ensuring that the scientific aims of the study are met. Contrast-sensitivity tests can provide useful information by revealing in some conditions visual loss not identifiable through visual acuity tests, by providing another method of monitoring treatments, and by providing a better understanding of visual performance problems faced by persons with vision impairment.

Contrast Sensitivity↗

PubMed1998

Objective measurement of contrast sensitivity function using contrast sweep visual evoked responses.

AIM/BACKGROUND: The contrast sensitivity function (CSF) measurement provides information that is not accessible by standard visual acuity determinations. The contrast sweep pattern reversal visual evoked responses (CSVER) technique was used to objectively measure the CSF in clinical practice. METHODS: The contrast thresholds were measured at five spatial frequencies in 10 normal subjects. The CSVER were recorded with sinusoidally modulated vertical gratings at 10 contrast levels (96, 64, 48, 32, 16, 8, 4, 2, 1, and 0.5%) presented in five spatial frequencies (0.5, 1.0, 2.0, 4.0, and 8.0 cycles per degree). Each of 10 contrast levels was displayed for 2 seconds at the desired spatial frequency. The CSVER amplitudes at the second harmonic were calculated by discrete Fourier transform. The results were compared with those obtained using a psychophysical method. RESULTS: An inverted U-shaped CSF which peaked at 2.0 cycles per degree with a contrast sensitivity of 34.5 (contrast, 2.9%) was observed. The CSF assessed electrophysiologically was 0.62 to 0.79 log units lower than the sensitivity measured using the psychophysical method. However, the overall shapes were highly correlated. CONCLUSION: One can objectively measure CSF with CSVER and this may be useful in patients in whom the psychophysical method is limited.

Adult↗

PubMed1995

Visual dysfunction in patients with mitochondrial myopathies. II. Contrast sensitivity function.

Contrast sensitivity function with stationary and temporally modulated (8 Hz) black and white vertical sinusoidal gratings was investigated in 11 patients with biopsy-confirmed mitochondrial progressive external ophthalmoplegia. To evaluate contrast sensitivity function results, the contrast sensitivity versus spatial frequency experimental data for each subject were fitted with a second-order polynomial, and the coefficients of the best-fitting function from normal and patient groups were compared. Patients with progressive external ophthalmoplegia, as a group, showed a decreased sensitivity at the intermediate spatial frequencies (i.e., around 1.4 c/deg) with stationary gratings and through a wider range of spatial frequencies with temporally modulated gratings. These findings were confirmed by analyzing contrast sensitivity functions from each individual. The study showed that contrast sensitivity function detects visual function abnormalities noninvasively in a number of patients with mitochondrial progressive external ophthalmoplegia with unaffected Snellen visual acuity.

Adult↗

PubMed1992

The common cold, pattern sensitivity and contrast sensitivity.

Results from two studies involving challenge with respiratory syncytial viruses showed that volunteers who developed colds were more sensitive to a visually distracting pattern presented prior to virus challenge than were volunteers who did not get a cold. Volunteers with sub-clinical infections reported more illusions after virus challenge than they had done before, whereas uninfected volunteers and those with colds tended to report fewer illusions on the second test. These effects did not occur when volunteers were challenged with either a coronavirus or rhinovirus. Overall, the results confirm that behavioural measures may be related to susceptibility to subsequent illness, and that viral infections may influence visual perception. They also show that the effects vary according to the nature of the infecting agent, which agrees with results from studies looking at other aspects of behaviour.

Adolescent↗

PubMed1987

Spatial scaling of central and peripheral contrast-sensitivity functions.

Contrast sensitivity was measured as a function of spatial frequency at various eccentricities in the nasal visual field. Eccentricity influenced resolution more for vertical gratings than for horizontal ones, demonstrating a nasal field anisotropy. When grating apertures and spatial frequencies were varied together, by changing viewing distance, peripheral and central contrast-sensitivity functions could not be entirely superimposed by scaling the spatial-frequency stimulus parameter. However, when gratings apertures were designed to project a standard-sized patch on a hypothetical vertical surface at an angle of 9 deg to the line of sight, the superimposition of central and peripheral contrast-sensitivity functions improved. Central and peripheral contrast-sensitivity functions can be superimposed by describing the grating stimulus with reference to this putative surface in terms of cycles per surface distance. The surface-scaling approach leaves a minor effect of eccentricity on contrast sensitivity for vertical gratings but readily accommodates the vertical-horizontal anisotropy in grating resolution. These findings suggest a novel functional role for gradients in the spatial sampling of the visual field, in relation to the internal representation of the structure and geometry of visible surfaces.

Humans↗

PubMed1985

Hemispheric lateralization of spatial contrast sensitivity.

Visuospatial contrast sensitivity was determined by the Arden grating chart in 23 patients with cerebral infarctions involving the primary visual cortex or visual association cortex. Subjects were classified into three groups according to their lesions: I, 6 patients with unilateral medial occipital or occipitotemporal lesions; II, 6 patients with left lateral parieto-occipital lesions; and III, 11 patients with right lateral parieto-occipital lesions. Contrast sensitivity was markedly reduced in Group III, especially in patients having hemispatial agnosia. Group I patients with hemispatial agnosia showed almost normal contrast sensitivity. Spatial contrast sensitivity appears to be more affected when the lesion has an influence on the nondominant lateral parieto-occipital cortex.

Adult↗

PubMed1987

The effect of cycloplegia on the visual contrast sensitivity function.

Contrast sensitivity assessment is one of several emergent techniques being considered for inclusion in a visual standards test battery for the Army, particularly for the evaluation of Army aviators. Since a cycloplegic refraction is required for initial selection of candidates for Class I and Class IA flying duty, it is important to determine what effect, if any, cycloplegia has on the contrast sensitivity function. There were 12 subjects tested, all officers in preparation for flight training who had passed a recent Class I flight physical. Contrast sensitivity functions were obtained under normal ambient conditions and in the presence of a glare source both under manifest and cycloplegic conditions. Cycloplegia produced a small reduction in contrast sensitivity under normal ambient conditions, and a greater reduction under glare conditions. For both conditions, the cycloplegia effect was greater for the higher spatial frequency gratings than for the lower.

Aerospace Medicine↗