Showing papers on "Contrast (vision) published in 1979"
TL;DR: The results indicated specificly that visual patterns can be made equally visible if they are scaled so that their calculated cortical representations become equivalent and the power law of spatial summation suggests the existence of a central integrator that pools the activity of cortical neurons.
Abstract: This study shows that photopic contrast sensitivity and resolution can be predicted by means of simple functions derived by using the cortical magnification factor M as a scale factor of mapping from the visual field into the striate cortex. We measured the minimum contrast required for discriminating the direction of movement or orientation of sinusoidal gratings, or for detecting them in central and peripheral vision. No qualitative differences were found between central and peripheral vision, and almost all quantitative differences observed could be removed by means of a size compensation derived from M. The results indicated specifically that (1) visual patterns can be made equally visible if they are scaled so that their calculated cortical representations become equivalent; (2) contrast sensitivity follows the same power function of the cortical area stimulated by a grating at any eccentricity; (3) area and squared spatial frequency are reciprocally related as determinants of contrast sensitivity; and (4) acuity and resolution are directly proportional to M, and the minimum angle of resolution is directly proportional to M-1. The power law of spatial summation expressed in (2) and (3) suggests the existence of a central integrator that pools the activity of cortical neurons. This summation mechanism makes the number of potentially activated visual cells the most important determinant of visibility and contrast sensitivity. The functional homogeneity of image processing across the visual field observed here agrees with the assumed anatomical and physiological uniformity of the visual cortex.
512 citations
TL;DR: The detectability of foveally presented low-contrast flickering stimuli was determined for glaucoma patients, ocular hypertensives, and normal control subjects and the average of the contrast sensitivities to these two simuli was consistently lower inglaucomatous than in normotensive eyes.
203 citations
TL;DR: It is suggested that a lesion in the central visual system does not always result in a complete and permanent loss of function and that systematic visual stimulation in the area between the intact and blind parts of the visual field leads to an improvement in visual performance.
Abstract: Patients with postchiasmatic visual field defects were trained at the border of their visual field. Using a psychophysical method, light-difference thresholds were determined repeatedly in this visual field area. Improvement in contrast sensitivity and increase in size of the visual field could be obtained by this training procedure. The improvement was confined to the trained visual field area and showed interocular transfer indicating its central nature. Althoughh only contrast sensitivity was trained, the observed improvement was not limited to this visual function. Visual acutity, critical flicker fusion, and colour perception also showed and improvement suggesting an association of these functions. The improvement was restricted to the training period-no spontaneous recovery was observed between or after the periods of training. It is suggested that a lesion in the central visual system does not always result in a complete and permanent loss of function. The critical level of function that normally has to be reached for sufficient neuronal sensitivity may be obtained by systematic visual stimulation in the area between the intact and blind parts of the visual field. This increase in neuronal sensitivity leads to an improvement in visual performance.
196 citations
TL;DR: Under optimum conditions, image stabilization elevates the subject's contrast threshold by a factor of about 20; it also produces after-images with resolution greater than 12 c/deg; these results compare favorably with those obtained by other methods.
Abstract: To demonstrate that eye movements have profound effects on the sine-wave contrast threshold, the author uses a new method of stabilizing the retinal image, in which the Purkinje reflections from the eye move the stimulus pattern displayed on a CRT screen. Calibration of this compensatory motion is very critical; a gain error greater than 1% may produce significant destabilization. Under optimum conditions, image stabilization elevates the subject’s contrast threshold by a factor of about 20; it also produces after-images with resolution greater than 12 c/deg. These results compare favorably with those obtained by other methods.
178 citations
TL;DR: Spatial contrast sensitivity functions were measured for hooded and albino rats in behavioral tasks in which the animals were required to discriminate sinusoidal luminance gratings from homogeneous fields of the same average luminance.
155 citations
TL;DR: It is suggested that contiguous regions of different luminance (and contiguous colour regions) are normally held in spatial register by locking from common luminance boundaries by producing inappropriate contour shifts from neighbouring regions of contrasting luminance when separated by narrow gaps of neutral luminance.
Abstract: The Cafe Wall illusion (seen on the tiles of a local cafe) is a Munsterberg chequerboard figure, but with horizontal parallel lines which may have any luminance separating the rows of displaced squares. These (the ‘mortar’ lines) display marked wedge distortion which is especially affected by: contrast of the squares (‘tiles’); width of the ‘mortar’ lines, and their luminance which must not be significantly higher than that of the light squares or lower than that of the dark squares for distortion to occur. An experiment is described from which quantitative data have been obtained by varying these parameters. It is suggested that contiguous regions of different luminance (and contiguous colour regions) are normally held in spatial register by locking from common luminance boundaries. The Cafe Wall illusion is attributed to this border locking producing inappropriate contour shifts from neighbouring regions of contrasting luminance when separated by narrow gaps of neutral luminance. Further implications on...
109 citations
TL;DR: It was found that the persistence of low- Contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated and at higher contrast levels, a tendency for persistence to be independent of contrast was observed.
Abstract: The visual persistence of sinusoidal gratings of varying spatial frequency and contrast was measured. It was found that the persistence of low-contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated. At higher contrast levels of 1 and 4 cycles deg-1 gratings, a tendency for persistence to be independent of contrast was observed. For 12 cycles deg-1 gratings, however, persistence continued to decrease with increasing contrast. These results are compared with recently published data on other temporal responses, and are discussed in terms of the different properties of sustained and transient channels.
109 citations
TL;DR: Eight patients with a subjective disorder of vision yet normal Snellen acuities after optic neuritis were shown to have an abnormal contrast sensitivity function in their affected eye.
Abstract: Eight patients with a subjective disorder of vision yet normal Snellen acuities after optic neuritis were shown to have an abnormal contrast sensitivity function in their affected eye. It appears that certain disorders of vision are associated with an abnormality of the contrast sensitivity function in spite of near normal visual acuity. Such an abnormality may affect pattern recognition without having an influence on Snellen acuity because of the high contrast of the latter and its predominant association with the higher spatial frequencies. Contrast sensitivity function is thus the only tool available to study those aspects of vision which have remained impervious to other subjective tests of visual function.
105 citations
TL;DR: Recent studies have shown that mammalian extrastriate visual cortex contains several anatomically and functionally distinct subregions, suggesting that a lesion in a homologous region might produce a defect in color vision while sparing other visual functions.
Abstract: In contrast to the traditional view that striate visual cortex (area 17) is surrounded by two homogeneous cortical areas (areas 18 and 19), recent studies have shown that mammalian extrastriate visual cortex contains several anatomically and functionally distinct subregions. One such region, the V-4 complex of the rhesus monkey, is highly specialized for the analysis of color information, suggesting that a lesion in a homologous region might produce a defect in color vision while sparing other visual functions.
We have studied a patient whose clinical syndrome supports this suggestion: a 44-year-old man with normal color vision suffered two cerebral infarctions that produced first a right and then a left superior homonymous quadrantanopia and also caused prosopagnosia, topographical disorientation, and severely impaired color vision. Computed tomography demonstrated extensive lesions in both inferior occipital lobes in the territories of the lateral branches of the posterior cerebral arteries, involving the lingual and medial occipitotemporal gyri bilaterally; these gyri contain the inferior portion of striate cortex and segments of extrastriate visual cortex. The patient had no difficulty in giving the correct color names associated with common objects presented either verbally or in outline drawings. Standardized testing with the Farnsworth-Munsell 100-hue test, the Nagel anomaloscope, and a method that tests for just-noticeable differences between monochromatic stimuli all showed that the patient's ability to distinguish one color from another was markedly impaired but not totally absent. In contrast, visual acuity, reading, visually guided eye movements, and stereopsis were normal. Cells in the V-4 complex of monkey extrastriate cortex are highly specialized for distinguishing one color from another; the hue discrimination deficit that was demonstrated in this patient with cerebral color blindness indicates that a region or regions with similar function has been damaged.
99 citations
Journal Article•
TL;DR: Binocular interaction experiments showed that binocular summation was absent at all contrast levels, but binocular occlusion was evident at high contrast levels for amblyopic observers, suggesting that two separate mechanisms detect gratings at high and low contrast levels.
Abstract: We have investigated suprathreshold contrast sensitivity and binocular interactions in strabismic and anisometropic amblyopes using a reaction time paradigm. For every spatial frequency, reaction time increased as the grating contrast decreased. At all spatial frequencies and contrast values the reaction times using the amblyopic eye were prolonged compared to the nonamblyopic eye, but most markedly at high spatial frequencies. In the middle range of spatial frequencies, the contrast vs. reaction time function for the nonamblyopic eyes was biphasic, suggesting that two separate mechanisms detect gratings at high and low contrast levels. These functions in deep amblyopia were monotonic, and in shallow amblyopia the break in the functions was present but shifted to lower contrast levels. Binocular interaction experiments showed that binocular summation was absent at all contrast levels, but binocular occlusion was evident at high contrast levels for amblyopic observers.
96 citations
TL;DR: Photopic contrast thresholds to sinusoidal gratings were measured in five goldfish by conditioning respiration in a Pavlovian paradigm, finding the limit of full summation previously found for the light-adapted goldfish.
Journal Article•
TL;DR: Comparison of the neonatal VEP results with behavioral data from 5-week-old infants, suggests little change in visual performance over the first month of life.
Abstract: Visual evoked potentials (VEPs) were recorded from a total of 97 1- to 10-day-old infants, with phase-reversing sinusoidal grating stimuli. The grating contrast or spatial frequency for which 50% of infants gave a statistically significant VEP was taken as a measure of threshold. This procedure yielded an estimate of neonatal acuity of 0.85 cycles/degree and an optimal contrast threshold of 50%. VEPs from an older infant showed good agreement with behavioral measures of sensitivity on the same individual. Comparison of the neonatal VEP results with behavioral data from 5-week-old infants, suggests little change in visual performance over the first month of life.
TL;DR: In this article, it was shown that the initial accommodation response to the out-of-focus, retinal image of a normal, wide-band target must be based on low spatial frequency information.
Abstract: Consideration of modulation transfer functions for the defocused eye and of contrast sensitivity at the retinal level suggests that the initial accommodation response to the out-of-focus, retinal image of a normal, wide-band target must be based on low spatial frequency information. As the response brings the retinal image of the target closer to optimal focus, higher spatial frequency information becomes available, allowing further refinement of the response. These ideas are illustrated by experimental studies of the accommodation responses to grating targets of various spatial frequencies.
TL;DR: The apparent contrast of suprathreshold grating targets was measured as a function of their spatial frequency and exposure duration, and the enhancement effect occurs foveally as well as for peripherally viewed targets, but it is abolished by decreasing the vertical extent of the grating.
TL;DR: The pain reaction to a new low osmolality contrast agent, sodium-methyl-glucamines-ioxaglate, in comparison to the conventional compound methylglucamine-ioxitalamate was tested and statistically evaluated in 12 patients using the visual analogue scale method.
Abstract: The pain reaction to a new low osmolality contrast agent, sodium-methyl-glucamine-ioxaglate, in comparison to the conventional compound methylglucamine-ioxitalamate was tested and statistically evaluated in 12 patients using the visual analogue scale method. The intensity of pain experienced was significantly smaller following intra-arterial injection of the compound of low osmolality as compared to the conventional contrast agent.
Journal Article•
TL;DR: Contrast threshold measurements have shown that there are two categories of spatial loss in amblyopia, that anisometropic and strabismic Amblyopia have a different neural basis, and that suprathreshold anomalies can occur independent of threshold defects.
Abstract: Contrast threshold measurements have extended our perspective of human amblyopia by focusing our attention on the perception of objects larger than the resolution limit. This approach has shown that there are two categories of spatial loss in amblyopia, that anisometropic and strabismic amblyopia have a different neural basis, and that suprathreshold anomalies can occur independent of threshold defects.
TL;DR: The results indicate that more highly reflective backgrounds permit somewhat greater legibility distances, and reflectorized backgrounds reduce the effect of changes in viewing conditions, which can be quite substantial in the case of non-reflective backgrounds.
Abstract: A laboratory study was carried out to define the effects of luminance, contrast, color, and driver visual characteristics on sign legibility distance. At the same time a computer model was developed which could predict the legibility distance of a sign, based on the laboratory data as well as geometric and photometric variables. A field study was then conducted in which legibility distance predicted by the model was compared with legibility distance measured on a number of real and simulated signs using a sample of normal drivers. In general, the predictions were within 10% of the measured legibility distances. The results indicate that more highly reflective backgrounds reduce the effect of changes in viewing conditions, which can be quite substantial in the case of nonreflective backgrounds. The contrast provided by the legend is very important. Luminance contrast requirements are lowest for highly reflective backgrounds and increase as background reflectivity decreases.
TL;DR: The tilt aftereffect was studied with adapting and test stimuli consisting of black or white bars, and of luminance edges, and both experiments failed to demonstrate selectivity of the TAE to the polarity of Luminance contrast.
Abstract: The tilt aftereffect (TAE) was studied with adapting and test stimuli consisting of black or white bars (experiment 1), and of luminance edges (experiment 2). Both experiments failed to demonstrate selectivity of the TAE to the polarity of luminance contrast.
TL;DR: In this article, a method of optical pseudocolouring of gray levels based on the addition of a coherent contrast reversed image and an incoherent image is proposed, and the principle of the method and the experimental set-up are described.
Abstract: A method of optical pseudocolouring of gray levels based on the addition of a coherent contrast reversed image and an incoherent image is proposed. The principle of the method and the experimental set-up are described and some experimental colour results are presented.
Patent•
21 May 1979TL;DR: In this paper, a photo-sensitive element is placed in front of the image surface of a light-directing device that selectively directs image light with increased intensity to microscopic, spaced-apart portions of the scene.
Abstract: The provision in front of the image surface of a photosensitive element of a device that selectively directs image light with increased intensity to microscopic, spaced-apart portions of the image surface yields a photograph or like record having a selectively decreased contrast. The photograph is viewed independently of its location relative to the light directing device. Changing the apparent aperture through which image light reaches the light-directing device can control the amount of contrast decrease. Further, selective filtering of a portion of the incident light separately controls the contrast of high-exposure portions of the image.
01 Dec 1979
TL;DR: The majority of applications of automatic visual inspection have been the case in which a high contrast image can be obtained, this will result from object silhouettes and high contrast reflectivity changes as in printed text.
Abstract: The majority of applications of automatic visual inspection have been the case in which a high contrast image can be obtained. This will result from object silhouettes 1 and high contrast reflectivity changes as in printed text. In these cases, the image can usually be successfully segmented by a threshold operation 2 , 3 leading to a two-level or binary image.
TL;DR: Monocular and binocular contrast sensitivity functions were determined behaviourly for normal kittens and those that were raised with alternating monocular exposure (alternators), suggesting that binocular summation depends on a normal population of binocular cortical units.
TL;DR: A relationship between abnormal binocular interaction during visual development and the organization of orientational mechanisms but does not explain the loss of visual acuity in amblyopia is suggested.
Abstract: In normal observers preadaptation to a parallel grating increases the contrast threshold for a line whereas a perpendicular grating has no effect. Such orientation selectivity was not found in the amblyopic eye of two out of five squinters. Only a weak after-effect produced with a grating parallel to the line was obtained in the good eye of four of the amblyopes while all of them show an abnormal threshold reduction following adaptation to a perpendicular grating. This suggests a relationship between abnormal binocular interaction during visual development and the organization of orientational mechanisms but does not explain the loss of visual acuity in amblyopia.
Patent•
10 May 1979TL;DR: A contrast enhanced color display apparatus, capable of providing a wide variety of colors, comprises a display means for emitting at least three colors and a color filter means disposed between the display means and a viewer.
Abstract: A contrast enhanced color display apparatus, capable of providing a wide variety of colors, comprises a display means for emitting at least three colors and a color filter means disposed between the display means and a viewer. The color filter means has a frequency selectivity characteristic which produces more attenuation at some non-emitted color frequencies than at other emitted color frequencies.
TL;DR: These experiments show that the smooth-pursuit system responds to changes in contrast in a similar way to the known response of direction-specific mechanisms, suggesting that the Smooth-p Pursuit system uses the signal generated by these mechanisms.
TL;DR: In a case of clinically fulminant multiple sclerosis, contrast-enhancing lesions were visible by computerized axial tomography (CT) and the patient died less than three weeks after the study, making neuropathologic correlation possible.
Abstract: In a case of clinically fulminant multiple sclerosis (MS), contrast-enhancing lesions were visible by computerized axial tomography (CT). The patient died less than three weeks after the study, making neuropathologic correlation possible. It appears that areas of contrast enhancement correlate in acute MS with early demyelinative lesions, and enhancement is related to breakdown of the blood-brain barrier. That such a disturbance is important in the pathogenesis of demyelination in MS has been suggested by other data as well. The characteristic CT findings of MS must therefore include enhancing lesions that reflect disease activity and that may be the only CT abnormality.
TL;DR: The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings.
Abstract: The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings in addition to the suprathreshold phenomenon of matching sinusoidal gratings of different spatial frequencies. This offers a unifying interpretation for why, at threshold conditions, the high spatial frequency portion of the image is blurred as severely by the nervous system as it is by the optics (e.g. Campbell and Green, 1965) while in extreme suprathreshold conditions the nervous system effectively deblurs the image (e.g. Georgeson and sullivan, 1975; Kulikowski, 1976). These conclusions do not necessitate a highly specific form of visual processing such as Fourier channeling.
Journal Article•
TL;DR: The measurement of contrast sensitivity using gratings is a new clinical procedure which yields information about the functioning of the visual system and preliminary clinical results are included.
Abstract: The measurement of contrast sensitivity using gratings is a new clinical procedure which yields information about the functioning of the visual system. Previously, this type of information has not been readily obtainable in the clinical environment. This article includes the basic concepts of measuring contrast sensitivity with gratings and preliminary clinical results.
TL;DR: In this paper, an extensive experimental study on the average contrast of speckle patterns produced by white light at the image plane is reported, which is determined by the complicated relationship between the spatial coherence of illuminating light, the point spread of an imaging system and the roughness properties of the objects.
Abstract: An extensive experimental study on the average contrast of speckle patterns produced by white light at the image plane is reported in this paper. The speckle contrast is found to be determined by the complicated relationship between the spatial coherence of illuminating light, the point spread of an imaging system and the roughness properties of the objects. It is found that the previous results of Sprague, Parry and Pedersen on white-light speckle patterns are realized only when the object is spatially coherently illuminated and a large number of scattering cells are involved within the point spread of the imaging system.
TL;DR: Photographs of sine wave fringes as well as devices designed to produce interference patterns directly on the retina must be factored out in order to determine whether residual effects on the visual system remain.
Abstract: Recently, alterations in contrast (modulation) sensitivity functions of patients with high refractive errors have been noted. For example, this seems to be a common finding in aphakia. In some measure the observed alterations are due to the effect of the corrective lens and the optics of the eyes. These optical effects (in addition to blur) must be factored out in order to determine whether residual effects on the visual system remain. The argument is applicable to photographs of sine wave fringes as well as devices designed to produce interference patterns directly on the retina. A simple means for largely correcting these lens effects is discussed.