Showing papers on "Contrast (vision) published in 1977"
TL;DR: In this paper, the authors presented threshold contrast sensitivity functions for 10 representative strabismic amblyopes and found that contrast sensitivity is depressed for only high spatial frequencies, including low spatial frequencies.
422 citations
TL;DR: In this article, the authors measured the contrast sensitivity of the human eye with sinusoidal grating targets of various spatial frequencies and found that the shape of the contrast-sensitivity function and its absolute values show good agreement among normal subjects, but the most interesting properties of this function cannot be attributed to the optics of the eye, but must be understood in terms of the image processing activities of the visual pathways.
Abstract: Like the modulation transfer function of man-made imaging devices, the contrast sensitivity of the human eye can be measured with sinusoidal grating targets of various spatial frequencies. Criterion-free psychophysical methods permit us to regard the contrast sensitivity as a direct measure of the subject's visual performance, independent of subjective factors. Under these conditions, not only the shape of the contrast-sensitivity function but also its absolute values show good agreement among normal subjects. However, the most interesting properties of this function cannot be attributed to the optics of the eye, but must be understood in terms of the image-processing activities of the visual pathways. The contrast-sensitivity function varies with the size, brightness, motion and flicker of the test target, with the adaptive state of the subject's retina, and with his eye-movements. Most of these effects can be explained in terms of known neurophysiology.
261 citations
TL;DR: In 48 patients with multiple sclerosis sine-wave gratings were used to test visual sensitivity for coarse, medium, and fine detail rather than measuring visual acuity for fine detail only, and in 20 patients the test revealed a visual defect of neural origin, qualitatively different from that caused by refractive error.
Abstract: In 48 patients with multiple sclerosis sine-wave gratings were used to test visual sensitivity for coarse, medium, and fine detail rather than measuring visual acuity for fine detail only, as in conventional clinical tests. In 20/48 patients the test revealed a visual defect of neural origin, qualitatively different from that caused by refractive error. In 11 of these 20 patients, visual sensitivity to detail of medium coarseness was markedly degraded, even though sensitivity to both coarse and fine detail was unimpaired. In 3 of these 20 patients visual sensitivity to coarse detail was selectively degraded. These visual defects could not be detected by the Snellen test, yet the patient might experience visual problems in everyday life and also experience distorted visual perception. Possible neural bases for these visual impairments are discussed. Since 8 of the 14 patients with selective loss showed no clinical evidence of visual involvement, the test can aid the earlier diagnosis of multiple sclerosis.
256 citations
TL;DR: In this paper, the authors show that the sensitivity of a high-contrast sinusoidal luminance grating produces a temporary, band limited loss in sensitivity centered around the adaptation frequency, and the decrease appears to be both narrower and more symmetrical than earlier reports suggest.
232 citations
01 Jan 1977-Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology
TL;DR: The capacity of the compound eye to perceive its spatial environment is quantified by determining the number of different pictures that can be reconstructed by its array of retinula cells, and an optimum parameterp is found, which is approximately that found by Snyder (1977) for threshold resolution of a sinusoidal grating at the ommatidial sampling frequency.
Abstract: The capacity of the compound eye to perceive its spatial environment is quantified by determining the number of different pictures that can be reconstructed by its array of retinula cells. We can then decide on the best compromise between an animal's capacity for fine detail and contrast sensitivity. The theory accounts for imperfect optics, photon noise, and angular motion limitations to acuity.
1.
There is an optimum parameterp = D Δ φ, whereD is the facet diameter andΔ φ is the interommatidial angle, for each mean luminance, angular velocity and mean object contrast. We find that this value ofp is approximately that found by Snyder (1977) for threshold resolution of a sinusoidal grating at the ommatidial sampling frequency.
2.
A diffraction limited eye (D Δ φ ≅λ/√¯3) is the optimum design only for those animals that are active in the brightest sunlight, and have a region of their eye that normally experiences low angular velocity, otherwise it is better to have a largerD Δ φ. λ is the wavelength of light in vacuum.
3.
The design of the flyMusca is consistent with that of an animal with high angular velocity.
160 citations
TL;DR: Anatomical and psychophysical data are consistent with the hypothesis that the human retina maximizes the reconstruction of different pictures over the range in luminance required for day and night vision.
133 citations
TL;DR: It was found that a pattern at its own contrast threshold can suppress temporarily a contralateral pattern, regardless of the contrast of the latter, and a near-threshold pattern is as effective as one that is four times greater in contrast.
Abstract: A series of three experiments was performed to determine the minimum contrast necessary for a grating pattern to engage in binocular rivalry with a dissimilar pattern presented to the other eye. It was found that a pattern at its own contrast threshold can suppress temporarily a contralateral pattern, regardless of the contrast of the latter. In a fourth experiment it was found that a near-threshold pattern is as effective, in terms of the duration of visibility, as one that is four times greater in contrast; only the average duration of suppression varied with pattern contrast. This last set of data extends the findings of others to near-threshold conditions and poses difficulties for models of binocular rivalry based on the notion of reciprocal inhibition.
108 citations
TL;DR: The need of older people for increased lighting during indoor tasks and night driving is discussed and perception of high‐ and mediumcontrast letters has changed little at age 40, but about twice as much light is needed to see low‐contrastletters at age 20.
Abstract: Visual acuity of persons aged 16 to 90 years was measured with Snellen letters of varied contrast at 10, 1, 0.1, and 0.01 fl chart luminances. Percentage losses of seeing with age were computed. At 10 fl luminance, perception of high- and medium-contrast letters has changed little at age 40, but about twice as much light is needed to see low-contrast letters as at age 20. By age 70, no 2-min-subtense (20/40) letters were seen at 0.01 fl luminance. The need of older people for increased lighting during indoor tasks and night driving is discussed. Language: en
72 citations
Journal Article•
TL;DR: The validity of the present letter acuity evaluation of visual function for patients in which intraocular scattering is involved is questioned after atmospheric-induced anoxia produced cornea edema.
Abstract: Corneal edema was produced by atmospheric-induced anoxia and the visual effect was assesed by conventional acuity tests and compared with contrast sensitivity measurements. For the degree of edema which this technique produced, contrast sensitivity was depressed for only high spatial frequencies and could be considered in terms of equivalent defocus. This was not the case ofr a greater degree of edema which was simulated by a diffuser with a particle size that mimics the diffraction effects from an edematous cornea. Equivalent blur was not applicable, since low spatial frequencies were also affected and the letter and contrast sensitivity tests gave radically different results. In the light of these findings, the validity of the present letter acuity evaluation of visual function for patients in which intraocular scattering is involved is questioned.
72 citations
TL;DR: Striped gratings and a bullseye were masked by stimuli that look unlike those patterns, but share orientational and spatial-frequency components with them, suggesting some aspects of visual processing may be distributed rather than local in the space-domain.
TL;DR: A quantitative comparison of the results for one- and two-dimensional gratings provides psychophysical evidence which is consistent with the existence of orientationspecific channels in the human visual system.
TL;DR: The findings of this study indicate that both the amplitude of the ERG and the ability to discriminate test lights decline rapidly and at approximately the same rate following the onset of constant illumination.
TL;DR: It is shown that the perceived width of the bars of one polarity can be changed independently of the width of bars of the opposite polarity both in the test grating and in the adaptation grating, and it is suggested that the human visual system processes positive and negative contrast polarities in independent channels.
Abstract: The investigation is concerned with the processing of light and dark bar patterns by the human visual system. A response phenomenon, the frequency shift effect, is studied with particular attention being given to the most suitable parametric description. Previous investigations of the effect showed that the perceived spatial frequency of a test grating pattern can be changed, transiently, after a period of adaptation to a grating of different frequency. In the present work it is shown that the perceived width of the bars of one polarity (i.e. light or dark) in the test grating can be changed independently of the width of bars of the opposite polarity both in the test grating and in the adaptation grating. It is shown that there is no simple interpretation of this result in terms of the spatial frequency spectra of the gratings. It is suggested that the human visual system processes positive and negative contrast polarities in independent channels. The results are discussed in relation to the on- and off-centre receptive field characteristics obtained in microelectrode recordings from vertebrate visual systems.
TL;DR: A mathematical model is developed to account for the major aspects of the hysteresis phenomenon and the key feature of the model is positive feedback among disparity sensitive cells generated by disinhibitory circuits.
TL;DR: Tests of the assumptions entailed in the random spatial disparity hypothesis of the stereophenomenon that occurs on viewing dynamic visual noise with an interocular delay support the hypothesis in opposition to 2 alternative hypotheses.
Abstract: This paper reports a series of tests of the assumptions entailed in the random spatial disparity hypothesis (Tyler, 1974) of the stereophenomenon that occurs on viewing dynamic visual noise with an interocular delay. The results support the hypothesis in opposition to 2 alternative hypotheses. A new stereophenomenon is reported in which reversed steromovement is perceived when viewing dynamic visual noise that has both an interocular delay and complementary contrast between the 2 eyes. Only the random spatial disparity hypothesis appears to account for this reverse stereophenomenon.
TL;DR: In this article, the effect of the point spread function on the average contrast of image speckle patterns is studied by varying its form depending on the optical imaging system, and it is shown that the form of the OP does not largely affect the image contrast.
TL;DR: The results indicate large individual differences in dependence of visual acuity on both luminance and contrast, and the relation of acuity in the partially sighted to medical diagnosis is discussed.
Abstract: Visual acuity (minimum target size for threshold visibility) was measured as a function of luminance, contrast, and distance in experiments using 16 partially sighted persons. The results indicate large individual differences in dependence of visual acuity on both luminance and contrast. Visual acuity often failed to change systematically with variations in the testing distance; the effects of contrast and luminence on visual acuity also frequently failed to show any systematic dependence on viewing distance. The relation of acuity in the partially sighted to medical diagnosis is discussed along with some practical implications.
TL;DR: In this paper, the authors measured the performance of two subjects using target lines in which the line width, overall contrast and edge-gradient are varied, and the results showed an optimum line width of about 15 min arc for achieving the best performance.
Abstract: Experiments are described in which vernier acuity performance is measured for two subjects using target lines in which the line width, overall contrast and edge-gradient are varied. The results show an optimum line width of about 15 min arc for achieving a best performance. Contrast is shown to be a significant factor in vernier acuity in agreement with other acuity measures. The results also show that edge-gradient is significant in vernier acuity contrary to earlier propositions.
TL;DR: An image stabilisation system was used to study basic temporal properties which are normally obscured by eye movements, indicating that the responses to all three stimuli are generated by similar mechanisms.
TL;DR: It is shown that under most conditions the visual range of contrast detail can be predicted by linear system theory, and that significant, noticeable degradation of visibility in clean air areas can occur with only a very small absolute increase in the attenuation coefficient due to pollution.
TL;DR: There is substantial evidence that the signals of colour opponent cells in the human visual system make a contribution to the brightness signal in perception space—in addition to the signal of the achromatic cells—to measure the colour-brightness—psychophysically.
01 Jan 1977
TL;DR: Grating detection was studied in two sisters with tapetoretinal degeneration, both had normal Snellen acuity scores, but the older complained of blurred vision, while the younger had no visual complaints.
Abstract: Grating detection was studied in two sisters with tapetoretinal degeneration. Both had normal Snellen acuity scores, but the older complained of blurred vision, while the younger had no visual complaints. In the older, a high spatial frequency deficit was found by both psychophysical and evoked potential methods, and a generalized foveal sensitivity loss was demonstrated by static perimetry. In contrast, the younger sister had normal grating detection and static perimetry results.
TL;DR: A novel way to achieve a continuous range of low frequency attenuation is introduced, which gives the observer control over a continuous change in contrast enhancement and greatly increases the versatility ofLow frequency spatial filtering.
Abstract: Contrast improvement in a coherent image enhancement system by very low spatial frequency attenuation is shown, demonstrating possible errors incurred by incorrect attenuation. A novel way to achieve a continuous range of low frequency attenuation is introduced. The variable attenuation is produced by constructing the spatial filter from polarizing material and altering the relative polarization between the object transparency illumination and the spatial filter. This technique gives the observer control over a continuous change in contrast enhancement and greatly increases the versatility of low frequency spatial filtering. Coherent imaging systems are usually contaminated by noise, and a simple way to reduce the noise content in the image is shown.
TL;DR: Contrary to findings for threshold measures of visual functioning in older adults, the 20 older adults showed a significantly larger simultaneous brightness contrast effect (p less than .05) than the 20 younger adults.
Abstract: The illusion of simultaneous brightness contrast was used to investigate age changes in contrast sensitivity under suprathreshold conditions. Contrary to findings for threshold measures of visual functioning in older adults, the 20 older adults (aged 60-79 yrs.) showed a significantly larger simultaneous brightness contrast effect (p less than .05) than the 20 younger adults (aged 17-26 yrs.). The increase in simultaneous brightness contrast in older adults is attributed to a degeneration of damping fibers in the visual system.
TL;DR: The results suggest that the newborn is sensitive not only to large border areas of high contrasting illumination but to finer configurational details of stimuli as well.
Abstract: Visual pursuit was used in studying the ability of newborn infants to discriminate levels of contrast. Ratings of the degree of eye and head following were made as subjects pursued facial targets which varied in terms of the degree of figure-ground contrast and the degree of contrast internal to the figure as defined by the presence or saliency of facial features. Differential pursuit mirrored the degree of contrast such that the strongest pursuit occurred to stimuli which had clearly discriminable facial detailing in addition to strong figure-ground contrast. These results suggest that the newborn is sensitive not only to large border areas of high contrasting illumination but to finer configurational details of stimuli as well.
TL;DR: Results indicate that ramp (gradual onset and offset) test flashes yield qualitatively different spatial summation functions than functions obtained with square-wave test flashes, which suggest the involvement of both excitatory and inhibitory factors in detection.
TL;DR: This paper showed that the rate of acquisition of the form discrimination varied inversely with the rates of reinforcement for the color discrimination, thus demonstrating a contrast effect in simultaneous discrimination learning, which is called the contrast effect.
Abstract: Pigeons were trained on a form discrimination that alternated across trials with an already-learned color discrimination, which was associated with different probabilities of reinforcement for different groups. The rate of acquisition of the form discrimination varied inversely with the rate of reinforcement for the color discrimination, thus demonstrating a “contrast effect” in simultaneous discrimination learning.
12 Oct 1977
TL;DR: It is argued that recognition of the present set of objects is visually equivalent to the detec-tion, and can be predicted from image quality data (displayed S/14, MTF) along that line, as a function of luminance and contrast in object space.
Abstract: As a realistic visual task subjects had to recognize military vehicles out of six. alternatives. Percentages of correct identifications were determined at three different observation distances in order to interpolate the distance required for 50% correct, which is taken as a measure of performance. The scenery was simulated indoors by slide-projection in favour of better control of conditions and faster procedure. The slides were photographed at the location of an earlier field trial. The performance of a. portable, image, intensifier was measured, in this way as a function of luminance and contrast in object space. It ap-pears that recognition of the present set of objects is visually equivalent to the detec-tion. of a circular disk, and can be predicted from image quality data (displayed S/14, MTF) along that line.