Contrast (vision)

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

Comparison of visual outcomes of 2 diffractive trifocal intraocular lenses.

Abstract: Purpose To compare the visual outcomes after cataract surgery with bilateral implantation of 1 of 2 diffractive trifocal intraocular lenses (IOLs). Setting Two clinical centers, Lisbon, Portugal. Design Prospective comparative case series. Methods Phacoemulsification with bilateral implantation of a Finevision Micro F IOL (Group 1) or an AT Lisa tri 839 MP IOL (Group 2) was performed. Over a 3-month follow-up, the main outcome measures were uncorrected distance visual acuity (UDVA), corrected monocular and binocular distance visual acuity, uncorrected intermediate visual acuity at 80 cm, distance-corrected intermediate visual acuity (DCIVA), uncorrected near visual acuity at 40 cm, distance-corrected near visual acuity (DCNVA), spherical equivalent (SE) refraction, defocus curves, contrast sensitivity, presence of dysphotopsia, and use of spectacles. Results Each group comprised 30 eyes (15 patients). The mean values at 3 months were UDVA, 0.03 logMAR ± 0.08 (SD) (Group 1) and 0.08 ± 0.12 (Group 2) ( P = .765); DCIVA, 0.04 ± 0.07 logMAR and 0.18 ± 0.18 logMAR, respectively ( P = .048); DCNVA, 0.03 ± 0.06 logMAR and 0.11 ± 0.08 logMAR, respectively ( P = .032); SE, −0.25 ± 0.30 diopter (D) and −0.02 ± 0.39 D, respectively ( P = .087). There was no significant difference in contrast sensitivity or dysphotopic phenomena between groups. Conclusions Both trifocal IOL models provided excellent distance, intermediate, and near visual outcomes. Monocular DCIVA and DCNVA appeared slightly better in Group 1. Predictability of the refractive results and optical performance were excellent, and all patients achieved spectacle independence. Financial Disclosure Neither author has a financial or proprietary interest in any material or method mentioned.

Detection of model flowers by honeybees: The role of chromatic and achromatic contrast

Abstract: Spatial acuity depends on several factors, the most important of which are the sampiing density of the photoreceptor array, defined in the compound eye as the interommatidial angle A q~, and the contrast sensitivity of the eye, which is determined mainly by the size of the visual field of a single ommatidium (for more details, see [1, 21). Because a single ommatidium measures no more than the average intensity of the light absorbed in it, two objects, one dark and one bright, will only be resolved if they project onto two different (neighboring) ommatidia, and therefore the anatomical limit of spatial resolution is 2A~b. In the bee, A O is 1.4 ° in the vertical direction and 2.8 ° in the horizontal direction [3], and thus the limit of spatial resolution is 2.8 ° and 5.6 °, respectively. A q~ can be determined not only with the help of anatomical measurements but, in addition, in behavioral experiments using high-contrast moving gratings. A tethered-flying insect's optomotor response reverses its direction when the spatial period of the grating is smaller than 2AO. The values obtained using this method agree well with those inferred from anatomical studies (for refs., see [1]). However, the finest possible resolution, the limit of which is set by 2Aq~, can only be realized if the difference in intensity (i.e., the contrast) perceived by the two neighboring ommatidia is high enough to be detected. Intensity contrast between two adjacent stimuli, also termed intensity modulation (m), is defined as the ratio between the modulation amplitude and the mean intensity of the two stimuli. This ratio can also be expressed as m = ( I 1 I 2 ) l ( I 1 +I2) (1)

Contextual Illusions Reveal the Limit of Unconscious Visual Processing

Abstract: The perception of even the most elementary features of the visual environment depends strongly on their spatial context. In the study reported here, we asked at what level of abstraction such effects require conscious processing of the context. We compared two visual illusions that alter subjective judgments of brightness: the simultaneous brightness contrast illusion, in which two circles of identical physical brightness appear different because of different surround luminance, and the Kanizsa triangle illusion, which occurs when the visual system extrapolates a surface without actual physical stimulation. We used a novel interocular masking technique that allowed us to selectively render only the context invisible. Simultaneous brightness contrast persisted even when the surround was masked from awareness. In contrast, participants did not experience illusory contours when the inducing context was masked. Our findings show that invisible context is resolvable by low-level processes involved in surface-brightness perception, but not by high-level processes that assign surface borders through perceptual completion.

Visual Surround Suppression in Schizophrenia

Abstract: Compared to unaffected observers patients with schizophrenia show characteristic differences in visual perception, including a reduced susceptibility to the influence of context on judgements of contrast - a manifestation of weaker surround suppression. To examine the generality of this phenomenon we measured the ability of 24 individuals with schizophrenia to judge the luminance, contrast, orientation and size of targets embedded in contextual surrounds that would typically influence the target’s appearance. Individuals with schizophrenia demonstrated weaker surround suppression compared to matched controls for stimuli defined by contrast or size, but not for those defined by luminance or orientation. As perceived luminance is thought to be regulated at the earliest stages of visual processing our findings are consistent with a suppression deficit that is predominantly cortical in origin. In addition, we propose that preserved orientation surround suppression in schizophrenia may reflect the sparing of broadly tuned mechanisms of suppression. We attempt to reconcile these data with findings from previous studies.