Topic
Contrast (vision)
About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: Comparison sensitivity measurements at 6 and 12 c/deg appear to be most useful in the assessment of patients who have undergone laser refractive surgery because defocus and optical aberrations primarily affect the higher spatial frequencies.
Abstract: PURPOSE: To study the utility of measurements of contrast sensitivity at different spatial frequencies as an index of visual recovery following refractive surgery. METHODS: Contrast sensitivity at 1.5, 3, 6, 12, and 18 c/deg was measured with the Stereo Optical FACT chart in 20 patients after photorefractive keratectomy (PRK) using the Nidek EC-5000 excimer laser system, and in 18 patients following laser in situ keratomileusis (LASIK). Contrast sensitivity was measured preoperatively and 1, 3, 6, and 12 months after surgery. RESULTS: Results showed a statistically significant reduction (P .1). In LASIK patients, decreased contrast sensitivity values 1 month after surgery were also obtained at all spatial frequencies. After 3 months, contrast sensitivity at 1.5 and 3 c/deg had recovered and did not differ significantly from preoperative values (P>.1), although contrast sensitivity at other frequencies remained reduced (P .1). CONCLUSIONS: Contrast sensitivity measurements at 6 and 12 c/deg appear to be most useful in the assessment of patients who have undergone laser refractive surgery because defocus and optical aberrations primarily affect the higher spatial frequencies.
127 citations
TL;DR: This work uses colour matches to demonstrate that departures from "colour constancy" are large and that it is possible to obtain the same colour shifts when the complex Mondrian pattern is replaced by a homogeneous grey field surrounding a test patch.
126 citations
TL;DR: The results suggest that suppressive spatial interactions in amblyopic vision extend over larger distances than in normal foveal vision, similar to peripheral vision of non-amblyopic observers, for targets of the same size.
126 citations
TL;DR: 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.
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.
125 citations
TL;DR: This work studied the chromatic and temporal responses in several different clusters of human visual field maps using functional magnetic resonance imaging to measure color and contrast response functions.
Abstract: Neurological case studies and qualitative measurements suggest that regions within human extrastriate cortex are specialized for different perceptual functions, including color. However, there are few quantitative measurements of human extrastriate color specializations. We studied the chromatic and temporal responses in several different clusters of human visual field maps using functional magnetic resonance imaging. Contrast response functions were measured for luminance [(L + M)-cone], red-green [(L - M)-cone] and blue-yellow (S-cone) modulations at various temporal frequencies. In primary visual cortex (V1), temporal responsivities to luminance and red-green modulations are approximately constant up to 10 Hz, but responsivities to blue-yellow modulations decrease significantly. In ventral occipital cortex (VO), all colors elicit strong responses, and, for each color, low temporal frequency modulations are more effective than high temporal frequency modulations. Hence, VO represents the full range of color information but does not respond well to rapid modulations. Conversely, in human motion-selective cortex (MT+) and V3A, blue-yellow modulations elicit very weak responses, whereas luminance and red-green high temporal frequency modulations are equally or more effective than low temporal frequency modulations. Hence, these dorsal occipital regions respond well to rapid modulations, but not all color information is represented. Similar to human motion perception, MT+ and V3A respond powerfully to all temporal frequencies but only to some colors. Similar to human color perception, VO responds powerfully to all colors but only to relatively low temporal frequencies.
125 citations