Contrast (vision)

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

Rhythmic modulation of visual contrast discrimination triggered by action

Abstract: Recent evidence suggests that ongoing brain oscillations may be instrumental in binding and integrating multisensory signals. In this experiment, we investigated the temporal dynamics of visual–motor integration processes. We show that action modulates sensitivity to visual contrast discrimination in a rhythmic fashion at frequencies of about 5 Hz (in the theta range), for up to 1 s after execution of action. To understand the origin of the oscillations, we measured oscillations in contrast sensitivity at different levels of luminance, which is known to affect the endogenous brain rhythms, boosting the power of alpha-frequencies. We found that the frequency of oscillation in sensitivity increased at low luminance, probably reflecting the shift in mean endogenous brain rhythm towards higher frequencies. Importantly, both at high and at low luminance, contrast discrimination showed a rhythmic motor-induced suppression effect, with the suppression occurring earlier at low luminance. We suggest that oscillations play a key role in sensory–motor integration, and that the motor-induced suppression may reflect the first manifestation of a rhythmic oscillation.

Visual dysfunction and its correlation with retinal changes in patients with Parkinson's disease: an observational cross-sectional study

Abstract: Objectives To evaluate visual dysfunction and its correlation with structural changes in the retina in patients with Parkinson's disease (PD). Methods Patients with PD (n=37) and controls (n=37) were included in an observational cross-sectional study, and underwent visual acuity (VA), colour vision (using the Farnsworth and Lanthony desaturated D15 colour tests) and contrast sensitivity vision (CSV; using the Pelli-Robson chart and CSV 1000E test) evaluation to measure visual dysfunction. Structural measurements of the retinal nerve fibre layer (RNFL), and macular and ganglion cell layer (GCL) thicknesses, were obtained using spectral domain optical coherence tomography (SD-OCT). Comparison of obtained data, and correlation analysis between functional and structural results were performed. Results VA (in all different contrast levels) and all CSV spatial frequencies were significantly worse in patients with PD than in controls. Colour vision was significantly affected based on the Lanthony colour test. Significant GCL loss was observed in the minimum GCL+inner plexiform layer. A clear tendency towards a reduction in several macular sectors (central, outer inferior, outer temporal and superior (inner and outer)) and in the temporal quadrant of the RNFL thickness was observed, although the difference was not significant. CSV was the functional parameter most strongly correlated with structural measurements in PD. Colour vision was associated with most GCL measurements. Macular thickness was strongly correlated with macular volume and functional parameters (r>0.70, p<0.05). Conclusions Patients with PD had visual dysfunction that correlated with structural changes evaluated by SD-OCT. GCL measurements may be reliable indicators of visual impairment in patients with PD.

Visual function tests, eye disease and symptoms of visual disability: a population‐based assessment

Abstract: Purpose: To examine associations between eye disease and tests of visual function with self-reported visual disability. Methods: The Blue Mountains Eye Study is a cross-sectional census-based survey of eye disease in two postcode areas in the Blue Mountains, west of Sydney, Australia. Of 4433 eligible residents, 3654 (82.4%) participated. Subjects had a detailed eye examination, including tests of visual acuity, contrast sensitivity, disability glare and visual field. Lens and retinal photographs were taken and graded according to standardized protocols for presence of cataract, early and late age-related maculopathy, glaucoma, diabetic retinopathy, retinal vein occlusion and other eye diseases. An interviewer-administered questionnaire included questions about perception of visual disability. Results: Scores on all tests of visual function significantly decreased with age (P < 0.0001). This decrease persisted for all tests except disability glare after excluding subjects with identifiable eye disease. The presence of one or more eye diseases was significantly associated with all (self-reported) measures of visual disability (trouble driving at night, difficulty recognizing a friend across the street, reading a newspaper or recognizing detail on television); mixed cataract (cortical and nuclear, or posterior subcapsular and nuclear) was associated with trouble driving at night and difficulty recognizing a friend across the street. A 10-letter (two-line) decrease in best corrected or presenting visual acuity was significantly associated with all self-reported measures of visual disability, as was a two-step decrease in contrast sensitivity. A five-point increase in points missing in the visual field was weakly but significantly associated with all self-reported measures of visual disability except trouble driving at night. Conclusions: Visual function declines with age. Impaired visual function was strongly, and eye disease relatively weakly associated with reports of visual disability.

The effects of age on spatial frequency perception in human subjects

Abstract: Visual performance was measured in sixty-six subjects aged from 5 to 94 years. The curve of contrast sensitivity against spatial frequency was obtained for each subject. This curve had a peak contrast sensitivity in the 2-6 c/deg (cycles/degree) range with the fall-offs to either side of the peak described, on a double logarithmic plot, by straight lines. With advancing age, the position of the peak sensitivity remained unchanged but there was an overall decrease in contrast sensitivity. The highest spatial frequency which could be perceived remained constant up to 50 years, thereafter it fell with increasing age. The slope of the low frequency straight line remained unchanged while that of the high frequency straight line fell with increasing age, i.e. the loss of contrast sensitivity was greater for middle range spatial frequencies than for higher spatial frequencies. The possible site of these changes, i.e. the optics of the eye, the retina/brain or higher decision making centres, is discussed.

Contrast in diaphanography of the breast.

Abstract: Diaphanography is an imaging technique used in diagnosis of breast disease including cancer. The breast is illuminated with low intensity light and the transmission pattern of red and near‐infrared radiation is detected, amplified, reconstructed and displayed in a monitor. The instrumentation for diaphanography has evolved empirically, mostly through clinical practice, without a very clear understanding of the scientific basis of the technique. This research is concerned with investigating theoretically the dependence of the contrast produced by a lesion in a diaphanography image on the size, depth at which a tumor is located, photon energy, and photon angular flux distribution. Contrast calculations using the dotcomputer code in a two‐dimensional geometry showed that decreasing the size of a tumor by 50% decreases the contrast by a factor of 3 and 4 for 695‐ and 853‐nm photons, respectively. Decreasing the size of the normal tissue where a tumor is imbedded by 25% (from 4 to 3 cm) does not change the contrast very much (less than 20%) for both 695‐ and 853‐nm photons. The contrast for 950‐ and 695‐nm photons is comparable while the values for 853‐nm photons are smaller by a factor of 5 for similar cases. The contrast was also found to be dependent on the angle at which the diffuse light is detected after it transverses the host tissue, maximum contrast was found for 695‐ and 853‐nm photons at about 55°. For a detection angle of 77° the contrast observed is 3× and 12× smaller for 695‐ and 853‐nm photons, respectively. For smaller angles such as 18° the contrast was found to be a factor of 2 and 4 smaller for 695‐ and 853‐nm photons, respectively. It was also found that a tumor perturbs the photon flux density over very short distances in normal tissue (the effect is very localized). The flux recuperates at a distance of about two diffusion lengths. The condition that the lesion must be located next to the skin surface where a detector or camera is placed overrides any other effect.