Showing papers on "Contrast (vision) published in 1976"

The measurement of spatial contrast sensitivity in cases of blurred vision associated with cerebral lesions

Abstract: Thirty-five patients with known cerebral lesions complained of recently acquired blurred vision. None of them had evident oculomotor or pupillary abnormalities, and each had intact central fields and normal visual acuity by conventional standards. Examination of spatial contrast sensitivity was carried out with sinusoidal grating patterns, by determining the minimum contrast between alternate light and dark bars required to distinguish the pattern from a homogeneous field. This was done at each of several spatial frequencies which were established by varying the width of the bars and hence the coarseness of the pattern. The contrast sensitivities were plotted as "visuograms" which, by analogy to audiograms, record the sensitivities in comparison to normal standards. Of the 35 patients, most showed significant losses, amounting to greater than 50 per cent elevation of contrast thresholds. Eighteen showed high frequency losses; 11 had uniform reductions over the entire visible spatial frequency range and 6 had selective frequency losses in the intermediate frequency ranges. These defects in spatial contrast sensitivity, which were not predictable from standard acuity scores, indicate that the visual symptoms in our patients may have been caused by damage to frequency-selective neural elements in the central visual systems. The method may be used to advantage in clinical investigations as well as in physiological investigations of the functional pathways subserving central vision.

The conditions required for the maintenance of binocularity in the kitten's visual cortex.

Abstract: 1. In young kittens, cortical neurones, which are usually binocularly driven, have their binocularity reduced if one eye is covered, or if the eyes are made strabismic or alternately occluded. Some of the factors causing these changes were analysed. 2. If the contrast of one retinal image is abolished with no difference in mean illumination, the input from that eye is virtually lost. 3. If one eye merely has its mean retinal illumination attenuated, that eye does not specifically lose its influence in the cortex, although there is a reduction in the proportion of binocular units. This change might partly be due to a difference in the timing of signals from the two eyes but is more likely to be caused by a difference in the strength of the discharges. 4. There is little change in binocularity if one image is dimmed but contrast is absent from both. 5. If contours of very different orientation fall simultaneously on corresponding retinal regions, binocularity breaks down, as in the case of strabismus or when different patterns are presented to the two eyes. But as long as the patterns on corresponding retinal points have similar orientation, even if the visual axes are misaligned, binocularity can be maintained. 6. If the eyes are not stimulated simultaneously, binocularity is reduced, even if the contours falling on the two retinae (at different times) are identical. 7. Roughly simultaneous stimulation, with roughly congruent patterns on the two receptive fields, are needed for the upkeep of binocular connexions on to cortical cells.

Visual contrast sensitivity of a 6-month-old infant measured by the evoked potential.

Abstract: THE visual contrast sensitivity of the human infant has previously been measured using behavioural methods, in which psychophysical thresholds have been inferred from visual preferences1. In this paper we report a preliminary investigation of contrast sensitivity, as measured by the amplitude of the evoked cortical response, in a 6-month-old infant. These results are compared with behavioural measurements on the same infant, and with adult data obtained psychophysically and from evoked cortical responses.

Measurement of surface roughness properties by using image speckle contrast

Abstract: As a practical monitoring tool for measurements of surface roughness properties, a new instrument is actually constructed on the basis of using the average contrast of image speckle patterns. With this instrument an experimental investigation on the contrast variation of image speckle patterns is conducted systematically for various surface roughnesses of the objects under different conditions of an optical imaging system. It is found that the roughness and correlation length of the objects can be precisely determined from the experimental curve of the contrast variation versus the point spread of the imaging system. The present method using image speckle patterns is superior to the previous one which uses the contrast variation of speckle patterns in the diffraction field.

Neural integration in the first optic neuropile of dragonflies

Abstract: 1. The transfer ofangular sensitivity from photoreceptors (retinula cells) to second order neurons (large monopolar cells — LMC's) is investigated by means of intracellular recordings from the retina and lamina ofHemicordulia tau. Angular sensitivity is measured by using a single point light source in two different ways. In the first, the constant intensity test flash method, responses to test flashes delivered at different angles of incidence are compared with the axial intensity/response function of the unit (Pig. 1). In the second, the off-axis intensity/ response function method, complete LMC intensity/response functions are derived at a number of angular inclinations toaxis (defined as the point of maximum sensitivity within the unit's visual field) (Fig. 4, 5). 2. The constant intensity test flash method shows that dragonfly retinula cells have a high angular sensitivity when compared to other insects. The horizontal and vertical acceptance angles are 1.46°±0.44 and 1.31°±0.23 respectively. Application of this same method to LMC's demonstrates that they retain retinal acuity for their angular sensitivity functionsappear to be the same as those of retinula cells (Pig. 2, Table 1). 3. The off-axis intensity/response functions show that the shape of the triphasic LMC response waveform depends upon the angular inclination of the stimulus to axis. The relative amplitudes of “on” transient and plateau (Pig. 3) vary independantly with angle (Pig. 4). The slope of the plateau response/log intensity curve decreases as the stimulus moves off axis but the “on” transient curve's slope remains relatively constant (Pig. 5). 4. Constant intensity test flash methods cannot measure LMC angular sensitivity because the slope of the response/log intensity curves depend upon stimulus inclination. The off-axis intensity/response function method shows that lateral inhibition narrows the LMC visual fields (Fig. 6) and angular sensitivity is increased during the transfer of visual information (Pig. 7). 5. Examination of the LMC response waveform (Fig. 8) and the intensity/response characteristics (Fig. 5) shows that two types of inhibition shape the response to square wave stimuli. Intracartridge inhibition acts at the level of the first synapses to attenuate the response to maintained stimuli. Intercartridge inhibition acts with a time delay to depolarise the LMC membrane and increase angular sensitivity. 6. It is concluded that LMC's integrate retinal input by acting as high sensitivity detectors of contrast differences within the spatial domain. Their role as an input to the visual system is discussed in relationship to visual behaviour and its experimental analysis.

On visual detection of light sources

Abstract: Experiments show that human beings are capable of detecting self-illuminating surfaces in their visual field, and that this capacity is based, to a great extend, on immediate processing by the visual system, rather than on a higher-level analysis. What are the physical parameters associated with this perception? The following factors are discussed; The highest intensity in the scene, absolute intensity value, local and global contrast, comparison with the average intensity, and lightness computation. All these factors are shown to be insufficient for explaining human's ability to identify light sources in their visual field. Finally, a method for accomplishing the source detection task in the so-called Mondrian world is presented.

Contrast Effects at Planar Interfaces

Abstract: Minerals are often known to be to a certain extent disordered structurally as can be deduced from the X-ray diffraction data and occasionally from high-resolution optical microscopy.

Abnormal visual resolution in the Siamese cat

Abstract: When tested behaviorally, Siamese cats display marked differences in contrast sensitivity compared to ordinary cats. Overall sensitivity is depressed, the high-frequency cutoff point is lower, and there is less falloff in sensitivity at low spatial frequencies. Optical factors may contribute to these differences, or they may be attributable to the well-established anatomical abnormalities within the visual system of the Siamese cat.

On differential phase contrast with an extended illumination source

Abstract: Images of periodic phase objects are calculated for oblique illumination, the scanning method of Dekkers and de Lang, and differential interference contrast. The close relation between the scanning method and oblique illumination is shown. All the methods are capable of resolving grating periods larger than λ/2a, where a is the numerical aperture of both the objective and the condenser lenses. Differential interference gives higher contrast for object periods below λ/a; contrast is slightly higher above λ/a with oblique illumination.

Luminance specifications for automobile instrument panels.

Abstract: To establish a minimum luminance level, a psychophysical procedure was used to establish the 95% correctness threshold for 95% of older drivers (ages ranged from 45 to 67). The correctness threshold and subject response times were obtained over eight letter luminance levels, four letter sizes, and three contrast ratios. The results showed that letters must be at least 0.64 cm high (at an 81.3–cm viewing distance) in order to be visible to 95% of the older drivers when letter luminance is set at 1.71 cd/m2. Response times declined as letter size, contrast ratio, and letter luminance increased beyond their threshold values. Although older drivers' visual acuity losses may be compensated by the use of corrective lenses, their losses in brightness and contrast sensitivity simply mean that they need about 10 times as much light as younger drivers.

Arthrography with Amipaque (metrizamide) and other contrast media. A roentgenographic and histologic evaluation in rabbits.

Abstract: Arthrography of the knee joint was performed in 30 rabbits for comparison of Amipaque (metrizamide) with Urografin 60% (meglumine-sodium diatrizoate), Isopaque Amin (meglumine-calcium metrizoate), Conray Meglumin 282 (meglumine iothalamate) and Dimer-X (meglumine iocarmate). Films taken at regular intervals show longer contrast duration, and less hydrarthrosis after injection of Amipaque. Minimal focal inflammatory reaction in the synovial membrane is found in many cases when the animals are sacrificed 1 day or 7 days after the injections. No significant difference can be found between the contrast media, and similar changes are also seen after injection of physiologic saline.

Method and apparatus for testing vision

Abstract: The disclosure relates to a method and apparatus for testing eyesight in the presence of controlled varying degrees of contrast at a target which is being viewed. The contrast ratio of the illumination of the portion of a target having a series of test patterns with respect to the illumination of the background of the target surrounding the patterns affects intraocular light scattering in a subject's eyes. In one disclosed embodiment an eye chart is provided which has opaque symbols on an illuminated background. By means of a transparent surface which is partly reflective, such as a half-silvered mirror, a veiling light is superimposed uniformly upon the light transmitted from the illuminated background of the target toward the subject's eyes. By varying the level of the background light or the veiling light or the darker (polarized) portions of the target pattern with a polarizing filter, or all, different contrast ratios of the light directed from the location of the target toward the subject's eyes can be presented. The disclosure additionally relates to the measurement of the effect of varying contrast ratios of a target on a subject's eyes by the use of a plurality of different charts, each having a background and a pattern thereon which provide a different contrast ratio to the subject's eyes.

An acquired color defect of the opponent-color system.

Abstract: An acquired unilateral color defect in a 22-year-old man has been investigated with standard clinical tests and by using techniques which, it is thought, test specifically for the sensitivity of the luminance and opponent-color systems. The spectral sensitivity of the defective left eye, using 1 degree 200 ms. test flashes on a white background, has a single broad peak at about 550 nm. and resembles the photopic luminosity curve; in contrast, the normal curve, measured in the same conditions, has three peaks at about 440, 520, and 600 nm. However, the subject's spectral sensitivity curve for detecting 20 Hz. flicker is quite normal and is similar to his curve for 200 ms. flashes. It has recently been proposed that the three peaks of the normal curve for 200 ms. flashes reflect the activity of the opponent-color system, whereas the single peak for flicker detection is related to the luminance system. The preceding observations may thus be interpreted in terms of a specific loss of the subject's opponent-color system and this would explain his poor color discrimination. His luminance system appears to be normal, and evidence is presented for the maintained function of red- and green-sensitive (but not blue-sensitive) cones. The spectral sensitivity of the subject's right eye is nearly normal, suggesting a precortical origin of the defect; however, there seems to be some abnormality in this eye, indicating a less developed form of the same defect.

Contour interaction and temporal masking in strabismus and amblyopia.

Abstract: Visual acuity of amlyopic eyes, measured under binocular viewing conditions, was improved by reducing the contrast of targets presented to the normal eye. Improvement was also obtained by adjusting the temporal relationship between inputs to the normal and amblyopic eye. Optimal acuity was obtained by alternately presenting targets to the two eyes at rates centered about 2 and 7 Hz. These results are interpreted in terms of binocular contour interaction and metacontrast suppression. They suggest that a portion of the amblyope's acuity loss during binocular viewing conditions results from excessive masking by the dominant normal eye.

On the site of strabismic suppression.

Abstract: A grating pattern presented to one eye of an individual capable of alternating suppression induces a visual aftereffect (contrast threshold elevation), even when the pattern is phenomenally suppressed from vision This finding indicates that strabismic suppression occurs within the visual system after the site of the aftereffect, and points out a similarity between strabismic suppression and binocular rivalry suppression

Luminance and contrast for sign legibility and color recognition

Abstract: A laboratory study of sign legibility has shown that a contrast of between 30 and 50 percent is required to maintain 75th percentile legibility. Legibility distance increased gradually with greater contrast to about 80 percent; above a luminance ratio of 5 to 1, legibility did not increase greatly. As ambient levels increased, legibility distance increased linearly with the logarithm of either the letter or the sign luminance, whichever was greater. Five color combinations were measured. This report gives additional results on color recognition and applies the effects of luminance and contrast to legibility distance for 11 color combinations, after corrections were made for letter and stroke, width. A method for estimating legibility was developed for black and white letter and sign combinations. The effects of luminance and contrast on color recognition at five ambient levels showed the need to increase luminance and contrast as ambient levels increase. Laboratory luminance data, confirmed by two sets of outdoor measurements, furnished a basis for determining the luminance ratios used in the legibility estimates. A basis for estimating glance legibility distance in relation to ordinary legibility (long viewing time) is suggested. /Author/

A New Measure of Television Display Quality Relatable to Observer Performance

Abstract: : This report describes a new, direct measurement method of determining the imaging quality of cathode-ray tube (CRT), line scan displays. This measurement was specifically developed as a more critical and realistic indicator of display quality. The measurement consists of recording the modulation contrast available on the display as a function of spatial frequency. An electronic sine wave generator produces a sine wave intensity pattern of the face of a CRT display. The display luminance distribution is scanned using a telephotometer or microphotometer depending on the size of the display. The modulation contrast of the display is obtained from the photometer scan for several spatial frequencies. The resulting graph showing modulation versus frequency is defined as the Sine Wave Response (SWR) Curve of the display. Since human vision is not linearly related to modulation, it is desirable to transform the modulation axis to another parameter which is linearly related to vision. This can theoretically be accomplished by transforming the modulation contrast to square root of 2 incremented Gray Shades. The resulting Gray Shade Response (GSR) indicates how many gray shades are visible as a function of spatial frequency.

Transsituational negative contrast

Abstract: Rats were shifted from 32% sucrose solution in one apparatus to a 4% sucrose solution in a different apparatus, and the performance of these animals was compared to rats that received the 4% solution in both situations. Transsituational negative contrast effects were found in both consummatory and instrumental measures of behavior and, in addition, these contrast effects were found to have some elements in common with both successive and simultaneous contrast effects, but were identical to neither.

Luminance profiles demonstrate nonlinearities of brightness perception

Abstract: A projector and cylindrical lens are used for displaying gratings and for simple demonstrations of Weber’s law, Fechner’s law, simultaneous contrast, and Fourier synthesis effects in vision.