Contrast-coding in amblyopia. I. Differences in the neural basis of human amblyopia

Hess, Robert F.; Bradley, A.; Piotrowski, Leon N

doi:10.1098/rspb.1983.0012

Cited by 71 publications

(14 citation statements)

References 17 publications

(18 reference statements)

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“…To this extent, the sensitivity of fMRI may not be the same for cellular loss confined to stimuli of just low and just high contrasts. Here, we concentrate on the processing of intermediate spatial frequencies where human contrast sensitivity is best, but where there is behavioral evidence both in humans [Baker et al, 2008;Harrad and Hess, 1992;Hess et al, 1983] and monkeys [Kiper and Kiopes, 1994] for amblyopic processing deficits. We show that the fMRI deficits in this spatial frequency range are greater at high contrasts.…”

Section: Discussionmentioning

confidence: 99%

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

Hess¹,

Li²,

Lu³

et al. 2010

Human Brain Mapping

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Although there is general agreement that the fMRI cortical response is reduced in humans with amblyopia, the deficit is subtle and has little correlation with threshold-based psychophysics. From a purely contrast sensitivity perspective, one would expect fMRI responses to be selectively reduced for stimuli of low contrasts. However, to date, all fMRI stimuli used in studies of amblyopia have been of high contrast. Furthermore, if the deficit is selective for low contrasts, one would expect it to reflect a selective M-cell loss, because M-cells have much higher contrast gain than P-cells and make a larger contribution to the threshold detection of stimuli of low spatial and medium temporal frequencies. To test these two predictions, we compared % BOLD response between the eyes of normals and amblyopes for low- and high-contrast stimuli using a phase-encoded design. The results suggest that the fMRI deficit in amblyopia depends upon stimulus contrast and that it is greater at high contrasts. This is consistent with a selective P-cell contrast deficit at a precortical or early cortical site.

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Section: Discussionmentioning

confidence: 99%

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

Hess¹,

Li²,

Lu³

et al. 2010

Human Brain Mapping

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“…[7][8][9] That is to say that amblyopes do not perceive their world to be simply reduced in contrast when viewing with their amblyopic eye. 10 Under binocular viewing conditions there is thought to be little or no contribution from the amblyopic eye due to a strong dominance of the fixing eye, a condition known clinically as suppression.…”

Section: -4mentioning

confidence: 99%

Is Suppression Just Normal Dichoptic Masking? Suprathreshold Considerations

Reynaud

Hess

2016

Invest. Ophthalmol. Vis. Sci.

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PURPOSE. Amblyopic patients have a deficit in visual acuity and contrast sensitivity in their amblyopic eye as well as suppression of the amblyopic eye input under binocular viewing conditions. In this study we wanted to assess the origin of the amblyopic suppression by studying the contrast perception of the amblyopic eye at suprathreshold levels under binocular and monocular viewing.METHODS. Using a suprathreshold contrast matching task in which the reference and target stimuli were presented to different eyes either simultaneously or successively, we measured interocular contrast matching in 10 controls and 11 amblyopes (mean age 35 6 15; 5 strabismics; 3 anisometropes; 3 mixed). This was then used as an index of the binocular balance across spatial frequency and compared against the contrast sensitivity ratio measured with the same stimuli.RESULTS. We observed that binocular matching becomes more imbalanced at high spatial frequency for amblyopes, compared with controls; that this imbalance did not depend in either group on whether the stimuli were presented simultaneously or successively; and that for both modes of presentation the matching balance correlates well with the interocular contrast sensitivity ratio (mean correlation coefficient of the slopes R ¼ 0.7125). CONCLUSIONS.The results from our amblyopes show comparable losses of contrast perception at and above threshold under these binocular viewing conditions across a wide spatial frequency range, much stronger than that observed for our controls. This occurs under conditions in which there should be no dichoptic masking. Furthermore, the matching contrast could be well predicted by the monocular contrast sensitivity. Altogether, this suggests that amblyopic suppression cannot be explained by normal dichoptic masking but rather an attenuation of the input.Keywords: interocular matching, amblyopia, qCSF, contrast constancy, suppression A mblyopia involves a loss of monocular vision and a suppression of the amblyopic eye's function under binocular viewing. There is debate about the causal relationship between these two factors. One possibility is that the suppression seen in amblyopia is a consequence of combining normal dichoptic masking with elevated contrast threshold in the amblyopic eye. Dichoptic masking depends on the level of suprathreshold contrast, so an elevated threshold in one eye (e.g., the amblyopic eye) would automatically result in imbalanced masking at all contrast levels, such that one eye (e.g., the fellow fixing eye) will always dominate over the other. We refer to this as the threshold hypothesis, as implemented by the offset subtraction model (see Appendix) where the primary deficit is the amblyopia and the secondary consequence is the binocular dysfunction.1,2 An alternate explanation is that the suppression results from anomalously large dichoptic inhibition of the amblyopic eye's input by the fellow fixing eye's input that in the long term results in a contrast threshold elevation in the amblyopic eye. We refer to this as the...

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“…Included within this group of measures are methods that measure spatial frequencies in the Fourier domain [30], those that measure a weighted color contrast based on the distance between chroma regions [31], and those that calculate the difference between a single pixel and a surrounding region or neighborhood [32,33]. Despite this range of methods, there is still little consensus on how to produce a single number that represents the contrast perception of an image through localized pixel or neighborhood values [29].…”

Section: Measuring Contrast Through Digital Imagesmentioning

confidence: 99%

Measuring the dynamics of contrast & daylight variability in architecture: A proof-of-concept methodology

Rockcastle

Andersen

2014

Building and Environment

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a b s t r a c tUnlike artificial light sources, which can be calibrated to meet a desired luminous effect regardless of latitude, climate, or time of day, daylight is a dynamic light source, which produces variable shadow patterns and fluctuating levels of brightness. While we know that perceptual impacts of daylight such as contrast and temporal variability are important factors in architectural design, we are left with an imbalanced set of performance indicators e and few, if any, which address the positive visual and temporal qualities of daylight from an occupant point-of-view. If visual characteristics of daylight, such as contrast and spatial compositions, can be objectively measured, we can contribute to a more holistic analysis of daylit architecture with metrics that complement existing illumination and comfort-based performance criteria. Using image processing techniques, this paper will propose a proof-of-concept methodology for quantifying contrast-based visual effects within renderings of daylit architecture. Two new metrics will be proposed; annual spatial contrast and annual luminance variability. Using 56 time-step instances (taken symmetrically from across the day and year) this paper will introduce a method for quantifying local contrast values within a set of rendered images and plot those instances over time to visualize hourly and seasonal fluctuations in contrast composition. Using the same 56 instances, this paper will also introduce a method for quantifying variations in luminance (brightness) between instances to measure fluctuations in brightness. This paper pre-validates each of the proposed methods by calculating annual spatial contrast and annual luminance variability across ten abstract digital models and comparing those results to the authors' own intuitive ranking.

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Contrast-coding in amblyopia. I. Differences in the neural basis of human amblyopia

Cited by 71 publications

References 17 publications

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

Is Suppression Just Normal Dichoptic Masking? Suprathreshold Considerations

Measuring the dynamics of contrast & daylight variability in architecture: A proof-of-concept methodology

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