Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Contrast and Phase Combination in Binocular Vision

Abstract: Background How the visual system combines information from the two eyes to form a unitary binocular representation of the external world is a fundamental question in vision science that has been the focus of many psychophysical and physiological investigations. Ding & Sperling (2006) measured perceived phase of the cyclopean image, and developed a binocular combination model in which each eye exerts gain control on the other eye's signal and over the other eye's gain control. Critically, the relative phase of the monocular sine-waves plays a central role. Methodology/Principal Findings We used the Ding-Sperling paradigm but measured both the perceived contrast and phase of cyclopean images in three hundred and eighty combinations of base contrast, interocular contrast ratio, eye origin of the probe, and interocular phase difference. We found that the perceived contrast of the cyclopean image was independent of the relative phase of the two monocular gratings, although the perceived phase depended on the relative phase and contrast ratio of the monocular images. We developed a new multi-pathway contrast-gain control model (MCM) that elaborates the Ding-Sperling binocular combination model in two ways: (1) phase and contrast of the cyclopean images are computed in separate pathways, although with shared cross-eye contrast-gain control; and (2) phase-independent local energy from the two monocular images are used in binocular contrast combination. With three free parameters, the model yielded an excellent account of data from all the experimental conditions. Conclusions/Significance Binocular phase combination depends on the relative phase and contrast ratio of the monocular images but binocular contrast combination is phase-invariant. Our findings suggest the involvement of at least two separate pathways in binocular combination.

Color Vision Defects in Ocular Hypertension and Glaucoma: Quantification With a Computer-Driven Color Television System

Abstract: • In order to detect early defects of color vision caused by increased intraocular pressure, a computer graphics device and color monitor system were used to measure color contrast sensitivity. The system determines the threshold chrominance of a colored grating in which there is no change in luminance. The study included 13 control subjects aged 10 to 57 years and 19 patients with ocular hypertension or glaucoma aged 20 to 58 years. In the 13 eyes with visual field loss, color contrast sensitivity was profoundly reduced when the grating colors fell on a tritan color confusion line. In the eyes without visual field loss, tritan color contrast sensitivity was reduced to an average level considerably below the extreme limits of the control group. These results were compared with those of other color vision tests and diagnostic criteria for glaucoma. The findings suggest that among the tests used, color contrast sensitivity testing was able to discriminate most effectively between patients who had retinal damage and the normal population.

The effect of glaucoma on central visual function.

Abstract: Glaucoma has traditionally been thought to affect peripheral visual function in its early stages and to spare central visual function until late in the disease process The basis for this assumption has been the reliance on Goldmann-type perimetry, a rather sensitive method for assessing the peripheral visual function, and on Snellen-type visual acuity measurements, a rather insensitive method of assessing central visual function This belief has persisted despite frequent complaints from patients with glaucoma that their central vision is disturbed Over the past two decades, several investigations of central visual functions and their anatomic substrate have challenged this assumption Histologic studies of the nerve fiber layer in eyes with glaucoma suggest that the number of ganglion cells subserving macular function is decreased even in early stages of the disease In addition, afferent pupillary defects (a gross measurement of macular nerve fiber function) may also be present in eyes with early glaucoma Several studies have demonstrated that color perception (largely mediated by the fovea) is defective in glaucoma Furthermore, defects in color perception may even precede the development of visual field abnormalities Seventy-eight percent of patients with early glaucomatous visual field defects were found to have a defect in color perception when tested with a desaturated D-15 color panel that tests only the central 15 degrees In addition, both chromatic and achromatic foveal perception channels are defective in eyes with glaucoma and even in some eyes of those with suspected glaucoma Contrast sensitivity has become recognized as an important component of visual function Partial loss of contrast sensitivity may cause a degradation in the quality of perception even though the Snellen visual acuity remains normal Although contrast sensitivity is not entirely a macular function, it has been shown that as little as 3 degrees of disturbance of the macula (eg, with macular degeneration or with an artificial central scotoma) will reduce the contrast sensitivity, suggesting that this modality is indeed mediated to a significant extent by this portion of the retina Spatial contrast sensitivity appears to be reduced in patients with glaucoma However, because of overlap and lack of a sharp cutoff measurement, present testing procedures fail to allow a clear distinction between the glaucomatous and normal populations Although reduced temporal contrast sensitivity has been demonstrated in glaucomatous eyes by others, I undertook a systematic investigation of this function in a large group of patients with glaucoma and with suspected glaucoma(ABSTRACT TRUNCATED AT 400 WORDS)