Showing papers on "Contrast (vision) published in 1978"
TL;DR: The results indicate that peripheral contrast sensitivity and acuity are inferior to foveal performance, because of the diminished cortical projection area.
Abstract: THE area of visual cortex devoted to the analysis of a con-slant-size region in the visual field diminishes progressively for more peripheral locations. The change is described quantitatively by the cortical magnification factor, which indicates the linear extent of cortex in mm corresponding to one degree of visual angle at various eccentricities (angular distances from the middle fovea). The human cortical magnification factor has been estimated by Cowey and Rolls1 from the data of Brindley and Lewin2, who mapped the phosphenes (sensations of light) caused in the lower nasal visual field by electrical stimulation of the human visual cortex. Building on these results, we have studied the spatial contrast sensitivity functions in man at various eccentricities. We used two methods: in one the retinal image sizes of the test gratings were kept similar at different eccentricities and in the other, the calculated sizes of cortical projections of the test gratings were made similar at different locations. Our results indicate that peripheral contrast sensitivity and acuity are inferior to foveal performance, because of the diminished cortical projection area.
390 citations
TL;DR: The non-spatial memory deficits that have been found after unrestricted lateral prefrontal lesions are due mainly to damage below the principal sulcus in the inferior prefrontal cortex, which appears so far to be limited largely to the spatial modality.
359 citations
TL;DR: It is concluded that lack of perception during saccadic eye movements made in normal contoured environments results primarily from the visual “masking” effect of a clear image before and/or after the eye movement acting on the grey-out during the eyemovement.
329 citations
Journal Article•
TL;DR: The results indicate that the magnitude and extent of the intra-resolution limit abnormality vary dramatically in cataract subjects and that, for some subjects, vision is abnormal for objects of all sizes.
Abstract: Contrast thresholds for a range of different spatial frequencies were compared with "acuity" tests for 10 subjects with uniocular senile cataract The results indicate that the magnitude and extent of the intra -^resolution limit abnormality vary dramatically in cataract subjects and that, for some subjects, vision is abnormal for objects of all sizes This finding indicates that the present acuity evaluation of vision with cataracts is inadequate because, in some cases, it grossly overestimates the nature of the visual world of the cataract patient
259 citations
Journal Article•
TL;DR: The CSF's measured provide evidence for the presence of a low-frequency fall-off at 2 and 3 months of age, and sensitivity to contrast was shown to increase between 1 and 3 years of age.
Abstract: The importance of assessing infant visual function is indicated by recent demonstrations that early visual experience in part determines the eventual state of adult visual function. It is argued that the contrast sensitivity function (CSF) could be a valuable index in the assessment of infant vision because it provides information concerning several aspects of vision. CSF's were measured in 1-, 2-, and 3-month-old infants. The "cut-off" spatial frequencies, which are estimates of visual acuity, were 2.4 cy/deg for 1-month-olds, 2.8 cy/deg for 2-month-olds, and 4.0 cy/deg for 3-month-olds. Sensitivity to contrast was shown to increase between 1 and 3 months of age. The CSF's measured also provide evidence for the presence of a low-frequency fall-off at 2 and 3 months.
235 citations
TL;DR: The detectability of compound gratings containing two sinusoidal components was compared to that of each component alone and the results are consistent with models postulating several sizes of receptive fields at each position in the visual field but not with model postulating only one size at each positions.
233 citations
TL;DR: It is concluded that optical and neural effects combine in normal viewing to produce saccadic suppression, and minimizing the optically originating effects of contour masking and retinal image smear failed to eliminate the considerable impairment of vision that occurs during a saccades.
133 citations
TL;DR: In the visual cortex of kittens that have received their only visual experience while wearing a high-power lens before one eye, most neurons are dominated by input from the normal eye, mimicking psychophysical results from human anisometropic amblyopes.
Abstract: In the visual cortex of kittens that have received their only visual experience while wearing a high-power lens before one eye, most neurons are dominated by input from the normal eye. Moreover, contrast sensitivity and resolving power are lower for stimulation through the originally defocused eye, mimicking psychophysical results from human anisometropic amblyopes.
130 citations
TL;DR: The contrast sensitivities to sine-wave grating stimuli were measured for 36 observers with ages in the range 8 to 67 years and the younger members of the group with normal vision were lesssensitive to low spatial frequencies and the older members were less sensitive to high spatial frequencies than the middle-aged observers.
Abstract: The contrast sensitivities to sine-wave grating stimuli were measured for 36 observers with ages in the range 8 to 67 years Thirty-one observers had normal, healthy vision while 4 were suffering from diabetic retinopathy and 1 had a early lens opacities and macular degeneration The younger members of the group with normal vision were less sensitive to low spatial frequencies and the older members were less sensitive to high spatial frequencies than the middle-aged observers The 5 observers with pathological conditions were less sensitive to most grating stimuli than those with normal vision
127 citations
115 citations
TL;DR: It is shown that a smaller area, measuring several just resolvable distances across, has to be stimulated before successive or simultaneous contrast detection is possible at all.
Abstract: Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6°, 21°, and 50° on the nasal horizontal meridian. The targets subtended from 30 × 30 minutes of arc up to 16° × 16°. We have found that the contrast detection thresholds depend critically on the extent of the target field. If this extent is large enough peripheral detection thresholds are on a par with those measured at the fovea, only the sensitivity range is shifted to lower spatial frequencies. We show that if the just resolvable distance at any eccentricity is taken as a yardstick, and field width and spatial frequency are scaled accordingly, then the spatio-temporal contrast detection thresholds become identical over the whole visual field. It is shown that a smallest area, measuring several just resolvable distances across, has to be stimulated before successive or simultaneous contrast detection is possible at all. Detection performance improves if the stimulated area is enlarged up to diameters of at least 102 just resolvable distances. The just resolvable distance correlates well with mean interganglion cell distance, and with the cortical magnification factor.
TL;DR: A model is proposed that permits the prediction of contrast detection thresholds for arbitrary spatial patterns and an explanation is offered for certain invariance properties of spatial contrast detection that seems to possess promising generality.
Abstract: A model is proposed that permits the prediction of contrast detection thresholds for arbitrary spatial patterns. The influence of the inhomogeneous structure of the visual field and a form of spatial integration are incorporated in the model. A hypothetical density function for the spatial sampling units, which specifies the distribution of these units with respect to both size and location, is described. The density function is compared with anatomical and electrophysiological knowledge of the density of retinal and cortical receptive fields. This density function permits a particularly lucid interpretation in terms of pattern processing. It can be considered as a system that permits simultaneous global and focal views of the surroundings. The density function, together with a schematized adaptation behaviour of single units, and an incoherent summation rule permit us to calculate a measure of the mass response, and consequently the threshold function. Predictions of the model are compared with recently obtained psychophysical data. In particular an explanation is offered for certain invariance properties of spatial contrast detection that seems to possess promising generality.
TL;DR: In this paper, contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6°, 12°, 21°, 32°, and 50° on the nasal horizontal meridian.
Abstract: Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6°, 12°, 21°, 32°, and 50° on the nasal horizontal meridian. The field subtended 4° × 4°. Spatial frequencies ranged from 0.25 cpd up to the resolution limit, temporal frequencies from 0.1 Hz up to the CFF. Mean retinal illuminance was 10 trolands. We find for these conditions: (i) For any eccentricity there exists a unique combination of spatial frequency and velocity for which the threshold is a minimum. (Extremes are 2 cpd and 2° s−1 at the fovea, and 0.5 cpd and 12° s−1 at an eccentricity of 50°. (ii) Acuity depends little on velocity, the CFF only little on spatial frequency. (iii) The higher the eccentricity, the higher the threshold for any drifting sine wave pattern. Except for this the qualitative threshold behavior as a function of spatial and temporal frequency is identical at the fovea and at eccentricities up to 50°. The thresholds double every 12° for spatial frequencies of 0.25–2 cpd. For a given spatial frequency the visual field is blind beyond a certain critical eccentricity. This critical eccentricity is a monotonically decreasing function of spatial frequency.
Journal Article•
TL;DR: The results show that the transient VER consists of a relatively simple waveform that is most easily characterized by the initial negative peak (N1) whose latency and amplitude vary with the contrast and spatial frequency of the grating.
Abstract: Transient visual evoked responses (VER's) to the appearance-disappearance of sinusoidal gratings have been investigated for a range of spatial frequencies Contrary to the results of previous studies, the results show that the transient VER consists of a relatively simple waveform that is most easily characterized by the initial negative peak (N1) whose latency and amplitude vary with the contrast and spatial frequency of the grating At spatial frequencies less than 3 cycles/degree (c/d) an additional short latency component appears in the response This component is maximum at 1 to 2 c/d, saturates at low contrast, and is insensitive to the precise position of the grating on the retina The results are related to the properties of transient and sustained channels assumed to exist in the human visual system
Journal Article•
TL;DR: 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 cortex contains several anatomically and functionally distinct subregions as mentioned in this paper, suggesting that 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.
TL;DR: It is argued that both electrophysiological and psychophysical evidence indicates that Weber behavior starts whenever some small fixed number of quantum absorptions occur within an area of 1 mean interganglion cell distance across.
Abstract: Contrast detection thresholds for moving sine wave gratings were obtained at the fovea and at eccentricities of 6°, 21°, and 50° on the nasal horizontal meridian. The targets subtended from 30 × 30 minutes of arc up to 16° × 16°. Mean retinal illuminance was varied between 10 and 0.01 trolands. The transition from the de Vries–Rose to the Weber region occurs in the far peripheral visual field at a 2–3 decades lower illuminance level than at the fovea. The spatio-temporal contrast detection thresholds become comparable over the whole visual field if the mean distance between retinal ganglion cells is taken as a yardstick, and field width, spatial frequency, and quantum density are scaled accordingly. This means that at scotopic illuminance levels coarse or medium gratings are preferentially detected at other than foveal locations. (The fine gratings cannot be resolved at all at such levels.) It is argued that both electrophysiological and psychophysical evidence indicates that Weber behavior starts whenever some small fixed number of quantum absorptions occur within an area of 1 mean interganglion cell distance across. Or, equivalently, if a fixed small number of “neural quanta” enters a 100 × 100 μm2 area of the visual cortex.
TL;DR: It appears that summation is reduced in situations where the available accommodative-vergence cues are weak, and binocular with monocular sensitivities over a wider range of luminances than has been considered before.
TL;DR: This modification of the Pneumotachography method is inexpensive and permits measurement on unrestrained animals by combining a close-fitting face mask with a built-on, lightweight flow transducer head.
Patent•
17 Aug 1978TL;DR: In this paper, a method for substantially increasing the dynamic range of contrast of an input sequence of pixels representative of an image is presented. But the method is limited to a single image.
Abstract: A system, and method, is disclosed for substantially increasing the dynamic range of contrast of an input sequence of pixels representative of an image. In a preferred embodiment a first circuit is responsive to an input sequence of pixels representative of an image for developing bias and gain parameters. These bias and gain parameters are respectively utilized by first and second function generators to generate bias correction signals and gain correction signals, respectively. A delay circuit delays the input sequence of pixels to synchronize said input sequence with the bias correction signals and the gain correction signals. A first expansion circuit expands in a first direction the range of contrast of the delayed input sequence of pixels as a function of the bias correction signals to produce a first contrast expanded sequence of pixels. A second expansion circuit expands in a second direction the range of contrast of the first contrast expanded sequence of pixels as a function of the gain correction signals to produce an output sequence of pixels which has a substantially expanded dynamic range of contrast in relation to the dynamic range of contrast of the input sequence of pixels.
Journal Article•
TL;DR: Contrast sensitivity functions for temporally modulated sine wave gratings were established at a variety of retinal eccentricities in three esotropic amblyopes with acuities in their amblyopic eyes of 20/50, 20/100, and 20/300 and shown to vary with eccentricity and the degree of amblyopia.
Abstract: Contrast sensitivity functions (CSF's) for temporally modulated sine wave gratings were established at a variety of retinal eccentricities in three esotropic amblyopes with acuities in their amblyopic eyes of 20/50, 20/100, and 20/300. CSF's were shown to vary with eccentricity and the degree of amblyopia. In the 20/50 amblyope, reduced CSF's were confined to the higher spatial frequencies and to the central 5 degrees of the retina. Given greater acuity deficits (e.g., 20/100 and 20/300), CSF's were depressed over the entire spatial frequency range tested, with the effects intruding farther into the peripheral retina than for the 20/50 amblyope. In addition, the detection of the temporal as well as the spatial modulation was depressed in the CSF's of the observers with severe amblyopia.
TL;DR: The results indicate that the apparent latency of luminance EPs to noise modulated light can hardly be used for diagnosis of MS, and suggest that an increased latency can be ascribed to several causes, only one of these being an increased conduction time due to demyelination.
TL;DR: The visual acuity, refractive state, and depth of focus of the dark-reared hooded rat's dark-adapted eye were determined by recording the responses of retinal ganglion cell axons in the optic tract, implying that objects from 7 cm in front of the eye to optical infinity are in equivalent focus.
TL;DR: It was found that the contrast sensitivity function for stereopsis is similar in shape to that for detection, suggesting that as far as contrast requirements are concerned the mechanisms of global stereopsis do not show a bias in sensitivity to any particular spatial frequency but instead require a constant level of suprathreshold contrast regardless of spatial frequency.
Abstract: Contrast thresholds for stereopsis from narrow-band-filtered random-dot stereograms were compared with contrast thresholds for simple detection of similar narrow-band noise. Centre frequencies of filters were in the range 2.5--15 cycles deg(-1). It was found that the contrast sensitivity function for stereopsis is similar in shape to that for detection, suggesting that as far as contrast requirements are concerned the mechanisms of global stereopsis do not show a bias in sensitivity to any particular spatial frequency but instead require a constant level of suprathreshold contrast regardless of spatial frequency.
TL;DR: Coloured afterimages were obtained after fixation of a neutral grey spot on a coloured surround, and it was found that simultaneous contrast colours can produce afterimages (successive contrast), and conversely, coloured afterimages can induce simultaneous contrast colour.
TL;DR: It is shown that whenever the masking grating stimulates other mechanisms than those concerned with the detection of the test stimulus, the ratio of Δ contrast (test/contrast) is not constant, thereby indicating a departure from Weber's law.
TL;DR: Direction-specific losses of contrast sensitivity for sinusoidal test gratings as a function of the contrast of asinusoidal adapting grating were found to be similar to those measured previously with square-wave gratings, and direction- Specific losses of Contrast sensitivity are restricted to limited ranges of spatial frequency.
Abstract: Direction-specific losses of contrast sensitivity for sinusoidal test gratings as a function of the contrast of a sinusoidal adapting grating were found to be similar to those measured previously with square-wave gratings. Furthermore, both relationships were similar to that between motion aftereffect duration and the contrast of sinusoidal adapting gratings, and all three sets of data can be fit by a single function. The function shows that the magnitude of direction-specific adaptation effects increases linearly with the logarithm of adapting contrast in the low contrast region, but is essentially independent of contrast once the contrast exceeds threshold by more than a factor of five—six. In addition, it was found that direction-specific losses of contrast sensitivity are restricted to limited ranges of spatial frequency.
TL;DR: A microcomputer-based instrument is described that provides visual stimuli for a CRT display and collects and processes response data and produces a variety of visual patterns to facilitate the study of the properties of visual neurons of several different animals.
Abstract: A microcomputer-based instrument is described that provides visual stimuli for a CRT display and collects and processes response data. The system produces a variety of visual patterns to facilitate the study of the properties of visual neurons of several different animals. The visual patterns include drifting sinusoidal or bar gratings, contrast reversal gratings, and diffuse light. By means of a keypad, the experimenter can select the visual pattern and its parameters, such as depth of modulation, spatial frequency, initial spatial phase, temporal frequency, and rotation angle.