The Binocular Summation of Chromatic Contrast

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 145-145 ◽  
Author(s):  
D R Simmons ◽  
F A A Kingdom
Keyword(s):  
Contrast Sensitivity ◽  
Detection Threshold ◽  
Luminance Contrast ◽  
Binocular Summation ◽  
Chromatic Contrast ◽  
Probability Summation ◽  
Investigative Ophthalmology ◽  
Contrast Thresholds ◽  
Detection Mechanisms ◽  
Neural Summation

The level of binocularity possessed by mechanisms sensitive to chromatic contrast is still unclear. Recent studies of stereopsis and chromatic contrast have suggested that stereopsis is maintained at isoluminance, although the contrast sensitivity and disparity ranges of chromatic stereopsis mechanisms are reduced compared to luminance stereopsis mechanisms. Rose, Blake, and Halpern (1988 Investigative Ophthalmology and Visual Science29 283 – 290) hypothesised a link between binocular summation (ie the superiority of binocular detection over monocular detection) and stereopsis. Is this link maintained with heterochromatic isoluminant stimuli? To address this question, the binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 Gabor patches were measured. The stimuli possessed different relative amounts of colour and luminance contrast ranging from isoluminance (red/green) to isochrominance (yellow/black) through intermediate values. It was found that, with these stimuli, binocular detection was well modelled by assuming independent mechanisms sensitive to chromatic contrast and luminance contrast. Furthermore, with isoluminant stimuli, levels of binocular summation were above those expected from probability summation between the eyes, thus providing evidence for binocular neural summation within chromatic detection mechanisms. Given that stereoscopic depth identification is impossible at contrast detection threshold with isoluminant heterochromatic stimuli, these results suggest that the link between stereopsis and levels of binocular neural summation may not be a particularly strong one. These results also provide clear evidence for the binocularity of chromatic detection mechanisms.

scholarly journals More than noise: Context-dependant luminance contrast discrimination in a coral reef fish (Rhinecanthus aculeatus)

2020 ◽  
Author(s):  
Cedric P. van den Berg ◽  
Michelle Hollenkamp ◽  
Laurie J. Mitchell ◽  
Erin J. Watson ◽  
Naomi F. Green ◽  
...  
Keyword(s):  
Contrast Sensitivity ◽  
Luminance Contrast ◽  
Individual Species ◽  
Diverse Range ◽  
Bright Spots ◽  
Context Dependent ◽  
Luminance Discrimination ◽  
Contrast Perception ◽  
Contrast Discrimination ◽  
Contrast Thresholds

AbstractAchromatic (luminance) vision is used by animals to perceive motion, pattern, space and texture. Luminance contrast sensitivity thresholds are often poorly characterised for individual species and are applied across a diverse range of perceptual contexts using over-simplified assumptions of an animal’s visual system. Such thresholds are often estimated using the Receptor Noise Limited model (RNL) using quantum catch values and estimated noise levels of photoreceptors. However, the suitability of the RNL model to describe luminance contrast perception remains poorly tested.Here, we investigated context-dependent luminance discrimination using triggerfish (Rhinecanthus aculeatus) presented with large achromatic stimuli (spots) against uniform achromatic backgrounds of varying absolute and relative contrasts. ‘Dark’ and ‘bright’ spots were presented against relatively dark and bright backgrounds. We found significant differences in luminance discrimination thresholds across treatments. When measured using Michelson contrast, thresholds for bright spots on a bright background were significantly higher than for other scenarios, and the lowest threshold was found when dark spots were presented on dark backgrounds. Thresholds expressed in Weber contrast revealed increased contrast sensitivity for stimuli darker than their backgrounds, which is consistent with the literature. The RNL model was unable to estimate threshold scaling across scenarios as predicted by the Weber-Fechner law, highlighting limitations in the current use of the RNL model to quantify luminance contrast perception. Our study confirms that luminance contrast discrimination thresholds are context-dependent and should therefore be interpreted with caution.

The Binocular Combination of Chromatic Contrast

Perception ◽  
10.1068/p5279 ◽  
2005 ◽  
Vol 34 (8) ◽  
pp. 1035-1042 ◽  
Author(s):  
David R Simmons
Keyword(s):  
Contrast Sensitivity ◽  
Chromatic Contrast ◽  
Linear Summation ◽  
Binocular Interactions ◽  
Contrast Thresholds

How is chromatic contrast combined binocularly? One index of binocularity is the binocular contrast summation ratio (BCSR), which is the improvement in contrast sensitivity with binocular rather than monocular presentation. Simmons and Kingdom (1998, Vision Research38 1063–1071) noted that BCSRs with some red-green isoluminant stimuli were suggestive of full linear summation. This suggestion was investigated further in four subjects by measuring binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 isoluminant (red-green) and isochromatic (yellow-black) Gabor patches. These Gabor patches had either vertically or horizontally oriented carrier gratings and were either dichoptically in phase (same coloured bars in binocular correspondence) or in dichoptic anti-phase (opposite coloured bars in binocular correspondence). Full linear summation would be indicated by BCSRs of 2 for the in-phase and close to 0 for the anti-phase conditions. Mean BCSRs at isoluminance were 1.93 and 0.90, respectively, for the in-phase and anti-phase stimuli with horizontal carriers, the former being consistent with full linear summation, but the latter not. Despite these results, BCSRs obtained with isoluminant and isochromatic stimuli under similar conditions were not statistically distinguishable from each other, although there was a tendency for summation at isoluminance with in-phase stimuli to be higher and anti-phase stimuli to be lower. These data fall short of demonstrating full linear summation of chromatic contrast between the eyes under all presentation conditions, but they do indicate that there are strong binocular interactions at red-green isoluminance, which are similar to, and possibly even stronger than, those obtained with luminance stimuli.

Contrast coding by cells in the cat's striate cortex: Monocular vs. binocular detection

1995 ◽  
Vol 12 (1) ◽  
pp. 77-93 ◽  
Author(s):  
Akiyuki Anzai ◽  
Marcus A. Bearse ◽  
Ralph D. Freeman ◽  
Daqing Cai
Keyword(s):  
Contrast Sensitivity ◽  
Small Proportion ◽  
Behavioral Contrast ◽  
Striate Cortex ◽  
Binocular Summation ◽  
Characteristic Analysis ◽  
Physiological Basis ◽  
Contrast Detection ◽  
Binocular Stimulation ◽  
Contrast Thresholds

AbstractMany psychophysical studies of various visual tasks show that performance is generally better for binocular than for monocular observation. To investigate the physiological basis of this binocular advantage, we have recorded, under monocular and binocular stimulation, contrast response functions for single cells in the striate cortex of anesthetized and paralyzed cats. We applied receiver operating characteristic analysis to our data to obtain monocular and binocular neurometric functions for each cell. A contrast threshold and a slope were extracted from each neurometric function and were compared for monocular and binocular stimulation. We found that contrast thresholds and slopes varied from cell to cell but, in general, binocular contrast thresholds were lower, and binocular slopes were steeper, than their monocular counterparts. The binocular advantage ratio, the ratio of monocular to binocular thresholds for individual cells, was, on average, slightly higher than the typical ratios reported in human psychophysics. No single rule appeared to account for the various degrees of binocular summation seen in individual cells. We also found that the proportion of cells likely to contribute to contrast detection increased with stimulus contrast. Less contrast was required under binocular than under monocular stimulation to obtain the same proportion of cells that contribute to contrast detection. Based on these results, we suggest that behavioral contrast detection is carried out by a small proportion of cells that are relatively sensitive to near-threshold contrasts. Contrast sensitivity functions (CSFs) for the cell population, estimated from this hypothesis, agree well with behavioral data in both the shape of the CSF and the ratio of binocular to monocular sensitivities. We conclude that binocular summation in behavioral contrast detection may be attributed to the binocular superiority in contrast sensitivity of a small proportion of cells which are responsible for threshold contrast detection.

scholarly journals Binocular Summation Is Intact in Intermittent Exotropia After Surgery

2021 ◽  
Vol 8 ◽  
Author(s):  
Meiping Xu ◽  
Yiya Chen ◽  
Yiyi Peng ◽  
Zhifen He ◽  
Jun Jiang ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
Visual Information ◽  
Threshold Level ◽  
Contrast Threshold ◽  
Binocular Summation ◽  
Intermittent Exotropia ◽  
Probability Summation ◽  
Spatial Frequencies ◽  
Significant Difference

Purpose: To determine binocular summation of surgically treated intermittent exotropia (IXT) patients by measuring the contrast threshold.Methods: We recruited 38 surgically treated IXT patients aged 8–24 years and 20 age-matched healthy controls. All participants had normal or corrected-to-normal visual acuity (Snellen ≥ 20/20) in both eyes. The IXT patients had undergone the surgery at least a year prior to the study. Twenty-one of them obtained good alignment and 17 experienced a recurrence of exotropia. We measured the observers' monocular and binocular contrast sensitivities (CS) at six spatial frequencies (1.5, 3, 6, 12, 18, 24 cycles/degree) as an index of visual information processing at the threshold level. Binocular summation was evaluated against a baseline model of simple probability summation based on the CS at each spatial frequency and the area under the log contrast sensitivity function (AULCSF).Results: The exo-deviation of IXTs with good alignment was −6.38 ± 3.61 prism diopters (pd) at 33 cm and −5.14 ± 4.07 pd at 5 m. For the patients with recurrence, it was −23.47 ± 5.53 pd and −21.12 ± 4.28 pd, respectively. There was no significant difference in the binocular summation ratio (BSR) between the surgically treated IXT patients, including those with good alignment and recurrence, and normal controls at each spatial frequency [F(2,55) = 0.416, P = 0.662] and AULCSF [F(2,55) = 0.469, P = 0.628]. In addition, the BSR was not associated with stereopsis (r = −0.151, P = 0.365).Conclusion: Our findings of normal contrast sensitivity binocular summation ratio in IXT after surgical treatment suggest that the ability of the visual cortex in processing binocular information is intact at the contrast threshold level.

Spatial structure of chromatically opponent receptive fields in the human visual system

1995 ◽  
Vol 12 (1) ◽  
pp. 103-116 ◽  
Author(s):  
Pascal Girard ◽  
Maria Concetta Morrone
Keyword(s):  
Temporal Frequency ◽  
Receptive Fields ◽  
Local Variation ◽  
Luminance Contrast ◽  
Response Curves ◽  
Chromatic Contrast ◽  
Phase Discrimination ◽  
Human Color Vision ◽  
Contrast Thresholds ◽  
Contrast Response

AbstractThis study investigates the receptive-field structure of mechanisms operating in human color vision, by recording visual evoked potentials (VEPs) to multiharmonic gratings modulated either in luminance or color (red-green). Varying the Fourier phase of the harmonics from 0 deg to 90 deg produced a family of stimulus profiles that varied from lines to edges. The stimuli were contrast reversed to elicit steady-state VEPS, and also randomly jittered (at a higher temporal frequency than the contrast reversal) to ensure that the evoked response resulted from the polarity reversal, rather than from local variation of luminance or color. Reliable VEPs were recorded from both luminance and chromatic stimuli at all phases, suggesting that the mechanisms sensitive to chromatic contrast and those sensitive to luminance contrast have both symmetric and asymmetric receptive fields. Contrast thresholds estimated by extrapolation of the contrast response curves were very similar to psychophysical thresholds for phase discrimination, suggesting that the VEP response is generated by mechanisms mediating phase discrimination. The results support the idea that human color mechanisms have receptive fields with a variety of spatial symmetries (including odd- and even-symmetric fields) and that these mechanisms may contribute to phase discrimination of chromatic stimuli in a similar way to what has been suggested for luminance vision.

Color and luminance increment thresholds in poor readers

2008 ◽  
Vol 25 (3) ◽  
pp. 481-486 ◽  
Author(s):  
STEPHEN J. DAIN ◽  
RICHARD A. FLOYD ◽  
ROBERT T. ELLIOT
Keyword(s):  
Luminance Contrast ◽  
Poor Readers ◽  
Chromatic Contrast ◽  
Colored Overlays ◽  
Visual Processes ◽  
Computer Based ◽  
Luminance Increment ◽  
Contrast Discrimination ◽  
Contrast Thresholds ◽  
Higher Sensitivity

The hypotheses of a visual basis to reading disabilities in some children have centered around deficits in the visual processes displaying more transient reponses to stimuli although hyperactivity in the visual processes displaying sustained reponses to stimuli has also been proposed as a mechanism. In addition, there is clear evidence that colored lenses and/or colored overlays and/or colored backgrounds can influence performance in reading and/or may assist in providing comfortable vision for reading and, as a consequence, the ability to maintain reading for longer. As a consequence, it is surprising that the color vision of poor readers is relatively little studied. We assessed luminance increment thresholds and equi-luminous red-green and blue-yellow increment thresholds using a computer based test in central vision and at 10° nasally employing the paradigm pioneered by King-Smith. We examined 35 poor readers (based on the Neale Analysis of Reading) and compared their performance with 35 normal readers matched for age and IQ. Poor readers produced similar luminance contrast thresholds for both foveal and peripheral presentation compared with normals. Similarly, chromatic contrast discrimination for the red/green stimuli was the same in normal and poor readers. However, poor readers had significantly lower thresholds/higher sensitivity for the blue/yellow stimuli, for both foveal and peripheral presentation, compared with normal readers. This hypersensitivity in blue-yellow discrimination may point to why colored lenses and overlays are often found to be effective in assisting many poor readers.

scholarly journals Chromatic contrast detection in spatial chromatic noise

2004 ◽  
Vol 21 (3) ◽  
pp. 291-294 ◽  
Author(s):  
GIANLUCA MONACI ◽  
GLORIA MENEGAZ ◽  
SABINE SÜSSTRUNK ◽  
KENNETH KNOBLAUCH
Keyword(s):  
Color Space ◽  
Average Energy ◽  
Axial Component ◽  
Chromatic Contrast ◽  
Noise Masking ◽  
Contrast Detection ◽  
Uniform Background ◽  
Signal Color ◽  
Contrast Thresholds ◽  
Detection Mechanisms

The spectral properties of chromatic-detection mechanisms were investigated using a noise-masking paradigm. Contrast-detection thresholds were measured for a signal with a Gaussian spatial profile, modulated in the equiluminant plane in the presence of spatial chromatic noise. The noise was distributed within a sector in the equiluminant plane, centered on the signal direction. Each stimulus consisted of two adjacent fields, one of which contained the signal, separated horizontally by a gap with the same average chromaticity as the uniform background. Observers were asked to judge on which side of the central fixation point the signal was displayed via a two-alternative, forced-choice (2AFC) paradigm. Contrast thresholds were measured for four color directions and three sector widths at increasing levels of the average energy of the axial component of the noise. Results show that contrast thresholds are unaffected by the width of the noise sector, as previously found for temporally modulated stimuli (D'Zmura & Knoblauch, 1998). The results are consistent with the existence of spectrally broadband linear-detection mechanisms tuned to the signal color direction and support the hypothesis of the existence of higher-order color mechanisms with sensitivities tuned to intermediate directions in color space.

Basic visual capacities and shape discrimination after lesions of extrastriate area V4 in macaques

1996 ◽  
Vol 13 (1) ◽  
pp. 51-60 ◽  
Author(s):  
William H. Merigan
Keyword(s):  
Contrast Sensitivity ◽  
Luminance Contrast ◽  
Form Discrimination ◽  
Chromatic Contrast ◽  
Lower Quadrant ◽  
Line Segments ◽  
Area V4 ◽  
Fold Reduction ◽  
Visual Testing ◽  
Made In

Abstractlbotenic acid lesions were made in four macaque monkeys in a region of cortical area V4 that corresponds to the lower quadrant of one hemifield. For visual testing, fixation locus was monitoredwith scleral search coils and controlled behaviorally to place test stimuli either in the lesionedquadrant or in a control location in the opposite hemifield. Some basic visual capacities were slightly altered by the lesions; there was a two-fold reduction of luminance contrast sensitivity as well as red-green chromatic contrast sensitivity, both tested with stationary gratings. On the other hand, little or no loss was found when contrast sensitivity for detection or direction discrimination was tested with 10–Hz drifting gratings nor was there a reliable change in visual acuity. Hue and luminance matching were tested with a spatially more complex matching-to-sample task, but monkeys could not learn this task in the visual field locus of a V4 lesion. If previously trained at this locus, performance was not affected by the lesion. In contrast to the small effects on basic visual capabilities, performance on two form discrimination tasks was devastated by V4 lesions. The first involved discriminating the orientation of colinear groups of dots on a background of randomly placed dots. The second involved discriminating the orientation of a group of three line segments surrounded by differently oriented line segments. Some selectivity of the deficitsfor form discrimination was shown by the lack of an effect of the lesions on a global motion discrimination. These results show that while V4 lesions cause only slight disruptions of basic visual capacities, they profoundly disrupt form discriminations.

Development of face discrimination abilities, and relationship to magnocellular pathway development, between childhood and adulthood

2013 ◽  
Vol 30 (5-6) ◽  
pp. 251-262 ◽  
Author(s):  
PAMELA M. PALLETT ◽  
KAREN R. DOBKINS
Keyword(s):  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
Face Processing ◽  
Luminance Contrast ◽  
Object Discrimination ◽  
Chromatic Contrast ◽  
Object Processing ◽  
Age Related ◽  
Visual Characteristics ◽  
Age Related Changes

AbstractThe current study tested the development of face and object processing in young children (mean age = 5.24 years), adolescents (mean age = 15.8 years), and adults (mean age = 21.1 years) using stimuli that were equated for low-level visual characteristics (luminance, contrast, and spatial frequency make-up) and methods that equate for difficulty across ages. We also tested sensitivity to luminance and chromatic contrast (i.e., thought to be mediated primarily by the subcortical Magnocellular (M) and Parvocellular (P) pathways, respectively) to determine whether age-related improvements in face or object discrimination were driven by age-related changes in the M and/or P pathways. Results showed a selective age-related improvement in face sensitivity and a relationship between age-related increases in face sensitivity and luminance contrast sensitivity. These results add to the mounting evidence that the M pathway may influence face processing.

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