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Showing papers on "Contrast (vision) published in 1981"


Journal ArticleDOI
TL;DR: Receptive field size and magnification have been studied in striate cortex of awake, behaving rhesus monkeys at visual eccentricities and it is found that a point of light projected onto foveal retina is “seen” by larger numbers of striate cortical cells than a point that is projected onto peripheral retina.
Abstract: Receptive field size and magnification have been studied in striate cortex of awake, behaving rhesus monkeys at visual eccentricities in the range of 5–160 min. The major findings that emerge are (1) magnification in the foveola achieves values in the range of 30 mm/deg, (2) mean field size is not proportional to inverse magnification in contrast with previous reports, and (3) the product, magnification X aggregate field size, is greater in central vision than in peripheral vision. Thus, a point of light projected onto foveal retina is “seen” by larger numbers of striate cortical cells than a point of light projected onto peripheral retina. Implications of these findings for visual localization and two-point discrimination are discussed.

448 citations


Journal ArticleDOI
TL;DR: Comparison increment thresholds were measured as a function of the background contrast of suprathreshold sine wave gratings at 2 and 8 c/deg and Weber's Law does not hold for contrast discrimination under any of the conditions studied.

288 citations


Journal Article
TL;DR: A high spatial frequency deficit was found from tests of the amblyopic eyes of all subjects and this defect decreased with spatial frequency and was correlated with the magnitude of anisometropia.
Abstract: Contrast sensitivity functions were measured for sinusoidal gratings from a sample of 10 anisometropic amblyopes. A high spatial frequency deficit was found from tests of the amblyopic eyes of all subjects. This defect decreased with spatial frequency and was correlated with the magnitude of anisometropia. Controls were instituted to rule out psychophysical method and residual defocus as possible causes of these effects. At low spatial frequencies, there were small differences between the two eyes. For some subjects, sensitivities of the amblyopic eyes appeared actually higher than normal whereas the reverse was found for most of the others. Additional tests demonstrated that the low-frequency differences could be accounted for by magnification differences (aniseikonia) between the two eyes. These findings are consistent with the idea that monocular contrast deprivation is the causal agent in anisometropic amblyopia.

190 citations


Journal Article
TL;DR: It is reported that a daily perceptual activity, which relies on lower spatial frequency information, is also adversely affected: as compared to young individuals, many older individuals require more contrast to detect a face and to discriminate between two faces.
Abstract: Previous work showed that despite good visual acuity, many healthy older people require more contrast to see gratings of low and intermediate spatial frequencies than do younger observers. Here we report that a daily perceptual activity, which relies on lower spatial frequency information, is also adversely affected: as compared to young individuals, many older individuals require more contrast to detect a face and to discriminate between two faces. Ocular pathology, optical changes within the eyeball, and variation in criterion are ruled out as explanations for the age-related elevation in threshold.

165 citations


Journal ArticleDOI
TL;DR: Responses to moving sinusoidal gratings, whose spatial frequency, velocity, and contrast were varied systematically, indicated that knowledge of one spatial an .d one temporal curve of a cell allows one to calcu late its response to any combination of spatial and temporal frequencies.
Abstract: I. Recordings were obtained from 108 cells near the border of areas 17 and 18 in anesthetized, paralyzed cats. Emphasis was placed on analyzing responses to moving sinusoidal gratings, whose spatial frequency, velocity, and contrast were varied systematically. In the presence of drifting gratings, about 30% of the cells responded with a periodic discharge at virtually all effective spatial and temporal frequencies. These neurons tended to be “simple,” to have very low levels of spontaneous activity, and to have the narrowest spatialand temporal-frequency response functions. Another 30% of the cells responded aperiodically at all but the lowest spatial and temporal frequencies. These cells tended to be “complex” and to have the broadest tuning curves. The remaining cells responded periodically over part of the range of effective frequencies, and could be simple, complex, or intermediate and difficult to classify. 2. For most of the neurons that responded appreciably to both directions of movement at the optimal orientation, the peak frequency (and shape) of spatialand/or temporal-frequency response functions differ by more than 0.3 octave for the two directions of movement. The peak frequency and/or bandwidth of the temporal response function for either direction may also depend on whether there is a pause between movements in the two directions. 3. The response of almost all cells increases linearly with contrast up to a saturation level. The threshold contrast shows little dependence on spatial frequency, but is a function of temporal frequency. The slopes of response-contrast functions are steepest at the optimal spatial or temporal frequencies and diminish at lower or higher frequencies. 4. The peak frequency and shape (bandwidth and high-frequency roll-off) of temporal-frequency response functions do not depend significantly on the spatial frequency used to make the measurement and the converse is true. Accordingly, it is possible to use a spatial-frequency tuning curve measured at fixed temporal frequency and a temporal curve measured at fixed spatial frequency to predict the spatial-frequency tuning curve that is obtained when all spatial frequencies are presented at the same velocity. This implies that knowledge of one spatial an .d one temporal curve of a cell allows one to calcu late its response to any combination of spatial and temporal frequencies. 5. The higher a cell’s best spatial frequency, the lower is the optimal velocity of movement at the best spatial frequency. The equation for the regression line that summarizes this correlation has velocity proportional to spatial frequency raised to the -5/4 power.

132 citations


Journal ArticleDOI
TL;DR: The perception of the apparent frequency of rotation of gratings of various spatial-frequencies and contrast is investigated and high spatial-frequency and low contrast gratings appear to move slower and an oscilloscope spot oscillating back and forth at a constant velocity appears to have a lower velocity in the peripheral field.

131 citations


Journal ArticleDOI
TL;DR: An adaptation method was used to determine the specificity of orientation-selective channels in the human visual system at different retinal eccentricities in both hemifields of each eye.
Abstract: An adaptation method was used to determine the specificity of orientation-selective channels in the human visual system at different retinal eccentricities (up to 16 deg) in both hemifields of each eye. For a vertical test grating, the elevation in contrast threshold produced by adapting to a high-contrast grating of the same spatial frequency but variable orientation was equated with the contrast levels of a vertical adapting grating that produced equivalent effects (equivalent-contrast transformation). This enabled comparisons to be made between the orientation tuning of the aftereffect at different retinal loci. For the spatial frequency employed (3 cycles deg-1), no systematic change in orientation selectivity was found as a function of either retinal eccentricity or the hemifield (and hence the cerebral hemisphere) stimulated.

113 citations



Journal ArticleDOI
TL;DR: The results suggest that the mechanism responsible for detecting low spatial frequencies has a gain characteristic similar to that of cat retina Y cells and that the mechanismsresponsible for detecting high spatial frequency has a loss characteristic similar for cat retina X cells, as found by Shapley and Victor.
Abstract: We measure threshold for a vertical test grating superimposed on a fixed-contrast horizontal background grating of the same spatial and temporal frequency The rate of change of this threshold with increasing contrast of the background grating is a measure of the contrast gain of the responding mechanism Large slopes (high contrast gains) occur when spatial frequency is low and temporal frequency is high; small slopes (low contrast gains) occur when both spatial and temporal frequencies are low and when spatial frequency is high This division of the spatiotemporal frequency domain into low- and high-gain regions is consistent with the transient/sustained dichotomy found in previous psychophysical studies Furthermore, our results suggest that the mechanism responsible for detecting low spatial frequencies has a gain characteristic similar to that of cat retina Y cells and that the mechanism responsible for detecting high spatial frequencies has a gain characteristic similar to that of cat retina X cells, as found by Shapley and Victor [J Physiol (London) 285, 275-298 (1978)]

74 citations


Journal ArticleDOI
Lo J. Bour1
TL;DR: The results indicate that dynamic accommodation is optimal for image contrast of intermediate spatial frequencies, and that steady-state accommodation is most stable for target contrast of somewhat less than 100%.

74 citations


Journal ArticleDOI
TL;DR: This investigation shows that contrast is an important parameter in CCTV reading performance; for many patients, even slight contrast reductions significantly reduce reading performance.
Abstract: Closed circuit television (CCTV) systems have proven useful in professional and recreational rehabilitation of the partially sighted. However, the parameters for optimum performance on such systems have not been examined. This investigation shows that contrast is an important parameter in CCTV reading performance; for many patients, even slight contrast reductions significantly reduce reading performance. Distance acuity is not a good predictor of CCTV reading performance, nor is performance on conventional contrast sensitivity measures. However, a commercially available test for contrast sensitivity (the Arden plates) may be useful for predicting CCTV reading performance.

Journal ArticleDOI
TL;DR: Overall, cod contrast detection compared very favourably with figures available for other species including man.
Abstract: The contrast discrimination of Gadus morhua L was studied by means of a cardiac conditioning technique Fish were trained to respond to a projected pattern of spots and the contrast of pattern and background then reduced until the minimum contrast required to elicit a response was established This was repeated at seven different background light levels to cover the range of light conditions naturally encountered by the cod The minimum detectable contrast decreased with increasing light level to a minimum of around 20% The contrast threshold curve showed a discontinuity at a light level of approximately 80 × 10-6 W sr-1 m-2 This was thought to be linked to the change from photopic to scotopic vision Significant differences were found in cod taken from two different locations Overall, cod contrast detection compared very favourably with figures available for other species including man Using the obtained contrast discrimination figures some estimates were made of the cod sighting distance of hypothetical targets under natural conditions

Journal ArticleDOI
TL;DR: Evidence was found that low-frequency structure in the visual world is perceived not by harmonic analysis but by detection of contrast gradients, supported by the thresholds of trapezoidal gratings, i.e. gratings which have regions of uniform luminance alternating with linear luminance ramps.

Journal ArticleDOI
TL;DR: The performance of young adult subjects was recorded when the photometric contrast of a task was altered using “realistic” methods and suggestions for practical lighting design were presented.
Abstract: The performance of young adult subjects was recorded when the photometric contrast of a task was altered using “realistic” methods. A general transfer function was obtained relating task contrast to performance. Based upon the transfer function and additional photometric measurements, suggestions for practical lighting design were presented.

Journal ArticleDOI
TL;DR: With advancing age, the position of the peak sensitivity remained unchanged but there was an overall decrease in contrast sensitivity, and the loss of contrast sensitivity was greater for middle range spatial frequencies than for higher spatial frequencies.
Abstract: Visual performance was measured in sixty-six subjects aged from 5 to 94 years. The curve of contrast sensitivity against spatial frequency was obtained for each subject. This curve had a peak contrast sensitivity in the 2-6 c/deg (cycles/degree) range with the fall-offs to either side of the peak described, on a double logarithmic plot, by straight lines. With advancing age, the position of the peak sensitivity remained unchanged but there was an overall decrease in contrast sensitivity. The highest spatial frequency which could be perceived remained constant up to 50 years, thereafter it fell with increasing age. The slope of the low frequency straight line remained unchanged while that of the high frequency straight line fell with increasing age, i.e. the loss of contrast sensitivity was greater for middle range spatial frequencies than for higher spatial frequencies. The possible site of these changes, i.e. the optics of the eye, the retina/brain or higher decision making centres, is discussed.

Journal Article
TL;DR: Investigation of the visual performance of human subjects during presentation of a digital display moving at constant velocity with regard to the stationary eye found that performance was improved by increasing digit size, decreasing exposure time, or increasing display luminance.
Abstract: The visual performance of human subjects has been investigated during presentation of a digital display moving at constant velocity with regard to the stationary eye. The display was presented for brief periods (10-80 ms) at different luminance levels (0.5-8 cd/m2), contrast levels (1-16), and display sizes (character height 12-24' of arc). The probability of correctly identifying the display decreased to 90% when the velocity reached 3-4 degrees/s. Performance was improved by increasing digit size, decreasing exposure time, or increasing display luminance. Theoretical arguments have been adduced to indicate the usefulness of the results in predicting performance during continuous display exposure.

Journal ArticleDOI
03 Sep 1981-Nature
TL;DR: It is reported here that ablation of cortical areas 17 and 18 in the cat results in severe selective deficits in binocular depth perception consistent with a loss of stereopsis.
Abstract: The massive visual projection to cortical areas 17 and 18 (striate and parastriate cortex) of the cat strongly suggests that these structures have a major role in visual processing. It is therefore paradoxical that ablation of these areas has been reported to result in very trivial deficits in their visual perception and behaviour1,2. In contrast to humans and monkeys, which show profound visual deficits after ablation of the visual cortex3–6, cats with similar lesions show essentially normal visual behaviour and are able to discriminate complex visual patterns. The only apparent effect of cortical lesions is a mild impairment of the visual acuity for gratings and a possibly greater reduction of vernier acuity7. In the past, the functional deficits resulting from lesions or ablations of various cortical structures have provided important clues to the function of many cortical areas, but recently a more detailed picture has emerged from electro-physiological studies of the properties of their constituent neurones. A striking aspect of most visual cortical cells in both cat and monkey is their specificity for horizontal retinal disparity8–10, the detection of which is a prerequisite for stereopsis11. This suggests that the visual cortex may play a major part in mediating stereopsis. We report here that ablation of cortical areas 17 and 18 in the cat results in severe selective deficits in binocular depth perception consistent with a loss of stereopsis.

Journal ArticleDOI
TL;DR: The results of behavioural experiments determining contrast sensitivity functions (CSFs) for the eagle Aquila audax and man at two low luminances are compared and the relatively poor performance of the eagle under these conditions may result from its adaptation to achieve high resolution in conditions of high luminance and contrast.

Patent
14 Jul 1981
TL;DR: In this paper, a chart and method for measuring and quantifying generalized visual sensitivity in terms of contrast sensitivity and spatial frequency response is presented, where a multiplicity of grating patches whose contrast varies sinusoidally for differing spatial frequencies.
Abstract: A chart and method for measuring and quantifying generalized visual sensitivity in terms of contrast sensitivity and spatial frequency response The chart contains a multiplicity of grating patches whose contrast, in terms of luminance, varies sinusoidally for differing spatial frequencies The threshold levels of contrast and spatial frequency at which the presence of gratings can be detected accurately defines generalized visual sensitivity

Journal ArticleDOI
TL;DR: In this article, an astronomic reflective telescope has been converted to a telephotometer and an adjustable stop with normal size of 1 mm is inserted, thus selecting a small portion of the target to be measured.

Journal Article
TL;DR: It is concluded that these vision changes can be attributed to the short-term occlusion experienced by all subjects during treatment and that grating stimulation did not contribute to this improvement.
Abstract: Single letter and linear acuity (near and distance) and contrast sensitivity were measured in 15 amblyopes (ages 5 to 12) before, during, and after four weekly 7 min sessions of CAM treatment Six of the children, however, played games over a homogeneous grey disc having the same space-averaged luminance as that of the striped stimuli Experimental and controls results were indistinguishable In a few subjects from both groups, contrast sensitivity and slight linear acuity improvement was observed We conclude that these vision changes can be attributed to the short-term occlusion experienced by all subjects during treatment and that grating stimulation did not contribute to this improvement

Journal ArticleDOI
TL;DR: The Arden grating test appeared to be a sensitive test of abnormal central visual function in patients with retinitis pigmentosa.
Abstract: Arden gratings were used to measure contrast sensitivity in 40 patients with retinitis pigmentosa whose Snellen visual acuity was 6/12 or better. When compared with a group of 30 normal subjects the patients with retinitis pigmentosa had substantially decreased contrast sensitivity, especially at high frequencies. The Arden grating test appeared to be a sensitive test of abnormal central visual function in patients with retinitis pigmentosa.

Journal Article
TL;DR: A He-Ne laser interference device for clinical measurements of the neural contrast sensitivity fraction (CSF) and the mean CSF for normal observers (95 eyes) is presented, and the data are compared with overall CS values from other authors.
Abstract: A He-Ne laser interference device for clinical measurements of the neural contrast sensitivity fraction (CSF) is described. The system uses planoparallel glass plates for the generation of sinusoidal gratings on the retina. Incoherent light from two light-emitting diodes is superimposed for reducing the contrast to a range from 2 X 10-3 to 0.5. The device is coupled with a microcomputer that calculates the contrast sensitivity (CS) and permits control of the system by a dialogue program. The mean CSF for normal observers (95 eyes) is presented, and the data are compared with overall CS values from other authors. Pathologic CSFs of three patients are shown as examples for the clinical application. For screening purposes the CS values for five spatial frequencies are compared with the normal CSF. And loss-of-contrast values are calculated.

Journal ArticleDOI
TL;DR: The chicken exhibits asymptotic sensitivity to spatial detail (with acuity at about 1.5 c/deg) within 48 h of hatching, in contrast to the gradual visual development found for kittens, monkeys, and humans.

Journal ArticleDOI
TL;DR: A linear Fourier analysis on grating response predicts the collicular cells' preference for movement of small objects on a cell population basis as a function of spatial frequency velocity and contrast.

Journal ArticleDOI
TL;DR: The contrast sensitivity function of each patient agreed with the subjective view of the patient about his visual impairment and it also corresponded with the examiners' evaluation of the customer's performance in different visual and visuomotor tasks.
Abstract: Spatial contrast sensitivity functions of 11 retinitis pigmentosa patients were studied. The patients represented 3 different stages of the disease: 1: in the very severely impaired patients the contrast sensitivity and grating resolution had decreased to a fraction of normal. 2: in severely impaired patients, who had lost peripheral field but had subjectively satisfactory vision in the central field, contrast sensitivity differed considerably from one patient to another, 3: some of the moderately impaired patients, who still had useful peripheral vision, had nearly normal contrast sensitivity in the central vision while they already had large ring scotomas. The severity of reduction in contrast sensitivity was poorly correlated with visual acuity, the size of the visual field and the age of the patient. Because contrast sensitivity function cannot be predicted by means of other clinical measurements, it should be included in evaluation of visual impairment due to retinitis pigmentosa. We also measured contrast sensitivity at low luminance levels: this procedure provided useful information for evaluation of vision in retinitis pigmentosa. The contrast sensitivity function of each patient agreed with the subjective view of the patient about his visual impairment and it also corresponded with the examiners' evaluation of the patient's performance in different visual and visuomotor tasks.

Journal ArticleDOI
TL;DR: Spatio-temporal sensitivity at and above threshold was investigated in a group of patients who exhibited visual loss secondary to uniocular congenital cataract which was present within the first year of life and later removed, demonstrating that stimulus deprivation amblyopia is more similar to that condition than to strabismic amblyopian.
Abstract: Spatio-temporal sensitivity at and above threshold was investigated in a group of patients who exhibited visual loss secondary to uniocular congenital cataract which was present within the first year of life and later removed. The results fall into two general categories depending upon the severity of the visual loss and in particular upon the nature of the temporal loss. In the group exhibiting less severe amblyopia, contrast sensitivity for high and medium spatial frequencies was attenuated to a similar extent for all temporal frequencies. In the group exhibiting more severe amblyopia no form vision a was present; only temporal perception remained. In these cases a greater loss of flicker threshold sensitivity occurred at higher temporal frequencies. Supra-threshold tests revealed that movement perception was effectively normal in both of these groups. These results demonstrate that stimulus deprivation amblyopia, while different in some respects from anisometropic amblyopia is more similar to that condition than to strabismic amblyopia Previous animal results derived from monocular lid suture in cat and monkey are compared with these findings.

Proceedings ArticleDOI
01 Apr 1981
TL;DR: An image enhancement algorithm that modifies the local luminance mean of an image and controls the local constrast as a function of the local brightness mean of the image and is combined with the processed highs component.
Abstract: In this paper, we develop an image enhancement algorithm that modifies the local luminance mean of an image and controls the local constrast as a function of the local luminance mean of the image. The algorithm first separates an image into its lows (low-pass filtered form) and highs (high-pass filtered form) components. The lows component then controls the amplitude of the highs component to increase the local contrast. The lows component is then subjected to a non-linearity to modify the local luminance mean of the image and is combined with the processed highs component. The performance of this algorithm when applied to enhance typical undegraded images, images with large shaded areas, and also images degraded by cloud cover will be illustrated by way of examples.

Journal ArticleDOI
Richard A. Matula1
TL;DR: This bibliography brings together in one place the widely dispersed literature on the effects of VDUs on the eyes.
Abstract: Visual display units (VDUs) have been reported to cause such eye difficulties as eyestrain, visual discomfort, and visual fatigue. In addition, there are effects on visual accommodation as well as effects arising from contrast and glare sensitivity. This bibliography brings together in one place the widely dispersed literature on the effects of VDUs on the eyes.