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At least 1,621 records · Page 90Linked to original sources
PubMed1984

Structural modeling of spatial vision.

A linear structural model of mechanisms underlying spatial vision was generated from the variance-covariance matrix of contrast sensitivity data. The data had been collected on a large group of observers ranging in age from 19 to 87 yr, using gratings of 0.5-16 c/deg spatial frequency. Structural models incorporating various numbers of spatial frequency-tuned mechanisms were compared, with a three-mechanism model giving the best account of the data. The same analysis was applied to contrast sensitivity data simulated from Wilson and Bergen's (1979) model. When the stimulated data covered 0.5-16 c/deg, only three mechanisms were needed to give a satisfactory account of the data; when the simulated data covered 0.25-16 c/deg, four mechanisms were required. Peak sensitivities and bandwidths of the mechanisms extracted from the simulated data resembled those extracted from the real, population data. This reinforces the idea that at an early stage of human vision a small number of spatially-tuned mechanisms are operative. In addition, the outcome of analyses with both real and simulated data illustrate the potential value of linear structural models for vision research.

Adult↗
PubMed1985

Color vision in squirrel monkeys: sex-related differences suggest the mode of inheritance.

Behavioral tests of vision in squirrel monkeys (Saimiri sciureus) reveal that there are widespread individual variations in color vision in this species. The variation has a sex-related component: whereas both trichromatic and dichromatic color vision occurs among female monkeys, males appear exclusively dichromatic. This finding suggests that, unlike humans, squirrel monkeys have only a single photopigment locus on the X chromosome.

Animals↗
PubMed1988

Albino spatial vision as an instance of arrested visual development.

Adult albinos and human infants share a number of common visual characteristics: both have low grating acuity, both lack a foveal pit (foveal hypoplasia), and both have much lower central cone densities than in the normal adult. We have explored the consequences of these characteristics by measuring both spatial and temporal contrast sensitivity in the central retina and by comparing central and peripheral grating and vernier acuities in two young adult albino subjects. To compensate for nystagmus, horizontally oriented patterns were employed. Both subjects had normal flicker sensitivities, but their central grating and vernier acuities were approximately five times worse than normal. At 10.0 degrees in the inferior visual field, however, vernier and grating acuities were normal for both subjects. Finally, the ratio of grating to vernier acuity in albino central vision fell within the normal foveal range, suggesting that albino central vision does not resemble the adult periphery. These results are consistent with the hypothesis that spatial processing deficiencies in albino central vision are a direct consequence of the increased spacing of their central cones. Our data are comparable to available psychophysical results obtained from infants of approx. 10 months of age, thus suggesting that the albino visual system may represent a case of arrested development.

Adult↗
PubMed1989

Tetrachromatic color vision in the goldfish becomes trichromatic under white adaptation light of moderate intensity.

Spectral sensitivity of the goldfish was measured under white room light of 5 lx and 1.5 lx illuminance, using a behavioral training technique. Compared with the result obtained under 25 lx (Neumeyer, 1984), the functions differed remarkably in the mid- and longwave spectral ranges. Under 1.5 lx, the longwave maximum was absent, and wavelength discrimination was impossible in the mid- and longwave range (between 555 and 663 nm). This indicates that the longwave cone type does not contribute to color vision in these conditions. Since discrimination ability was not affected in other spectral ranges, we conclude that color vision is trichromatic then, being subserved by the ultraviolet, the short- and the midwave cone types only. Under 5 lx, the longwave cone type contributes to color vision, but, as shown in color mixture experiments, to a lesser extent.

Adaptation, Ocular↗
PubMed1992

The Bezold-Brücke effect in the color vision system of the honeybee.

Evidence is presented that intensity dependent color shifts (Bezold-Brücke effect) occur in the color vision system of the honeybee. The evidence comes from a fit between the choices of monochromatic lights in training experiments (Menzel, R., 1981; Journal of Comparative Physiology A, 141, 389-393) and the choice percentages derived now from recently presented quantitative predictions from the color opponent coding (COC) model for the bee (Backhaus, W., 1991; Vision Research, 31, 1381-1397) for the Bezold-Brücke effect. The only open parameter in the simulations of the training experiments is an experiment type dependent factor describing the weighting of color differences (judgement values) in the choice behavior. The results show (1) that the Bezold-Brücke effect exists in the bee. The results (2) confirm the color opponent coding (COC) model which was developed to describe the physiological components of the color vision system in the bee, (3) the general psychophysical assumptions about the structure of the color space, (4) the color difference formula, and (5) the general psychophysical assumptions about the (triadic) structure of judgements as tested in color similarity experiments.

Animals↗
PubMed1994

Biological aspects of bird colouration and avian colour vision including ultraviolet range.

Many diurnal birds possess a set of four spectrally different types of cone photoreceptor. The spectral range of vision is extended into the UV by a UV receptor. We have investigated the spectral properties of plumage colours including the UV by reflection spectroscopy. Some basic general principles of colour vision indicate that plumage colours are tuned to avian colour vision.

Animals↗
PubMed1996

Characterization of spatial aliasing and contrast sensitivity in peripheral vision.

Psychometric performance was measured for contrast detection and spatial resolution tasks in foveal and peripheral vision. Objective evidence was obtained for a quantitative difference between resolution acuity and detection acuity in the peripheral field. These two types of spatial acuity differed by up to an order of magnitude (3 vs 30 c/deg at 30 deg eccentricity) and they varied with stimulus contrast in distinctly different ways. Contrast sensitivity at the resolution limit was an order of magnitude above the absolute threshold of unity and the shape of the contrast sensitivity function was significantly different from that measured for foveal vision. The results suggest that current models of eccentricity scaling of contrast sensitivity be re-evaluated to take account of the extensive aliasing zone of spatial frequencies which becomes functional in peripheral vision when the retinal image is well focused.

Contrast Sensitivity↗
PubMed1984

Colour-spatial vision.

A critical survey is made of neurophysiological and psychophysiological investigations of colour vision. A neuronal model of colour-spatial vision is suggested. The model allows a unified explanation of the whole range of psychophysiological phenomena: the mixing of colours of high-frequency image components, the McCollough type colour after-effects, the simultaneous and successive colour contrast, the hue constancy perception, the appearance of non-spectral colours by mixing of monochromatic lights. A suggestion is made as to the existence of two main mechanisms of colour vision. The first of these, by means of Fourier transforms, gives a set of coefficients which describes the spatial distribution of light (quantity of energy) and hue (quality of energy) in the visual field. The second mechanism establishes colour names in each chromatically homogenous area of the field described by the first mechanism. Both mechanisms cooperate on the basis of their common spatial organization.

Color Perception↗
PubMed1987

Plasticity of monocular and binocular vision following cerebral blindness: evoked potential evidence.

Using monocular and dynamic random dot correlogram (DRDC) stimuli, sequential visual evoked potentials changes were demonstrated in 2 patients following cerebral blindness. The recovery of binocular vision was delayed in comparison to the recovery of monocular vision. The results are not due to simple acuity impairment or convergence deficiency, and thus provide evidence for the vulnerability of postsynaptic cortical mechanisms of human binocular vision.

Adult↗
PubMed1995

Colour vision loss in workers exposed to elemental mercury vapour.

We evaluated colour vision in 33 workers exposed to elemental mercury (Hg) vapour and in 33 referents matched for sex, age, alcohol consumption and cigarette smoking. The results were expressed as colour confusion index (CCI). In the workers urinary excretion of Hg (HgU) ranged from 28 to 287 micrograms/g creatinine. Subclinical colour vision loss, mainly in the blue-yellow range, was observed in the workers. This effect was related to exposure, as indicated by the correlation between HgU and CCI (r = 0.488, P < 0.01). In the workers whose HgU exceeded 50 micrograms/g creatinine, mean CCI was significantly increased compared to the matched referents. The results suggest that exposure to elemental Hg inducing HgU values exceeding 50 micrograms/g creatinine can induce a dose-related colour vision loss.

Adult↗
PubMed2006

Responsibility ascriptions and Vision Zero.

Vision Zero is a traffic safety policy that was adopted by the Swedish Parliament in 1997. Similar policies have been adopted in Norway and Denmark. In essence, Vision Zero states that it is unacceptable for anyone to die while using the road transport system. The policy also introduces an explicit distribution of responsibility for traffic safety, in which the system designers are ultimately responsible. In this article, it is argued that the proposed new distribution of responsibility can be better understood if we distinguish between two general types of responsibility ascriptions, namely backward-looking and forward-looking responsibility ascriptions. Both types include some kind of causal responsibility and whereas backward-looking responsibility implies an element of blame, forward-looking responsibility implies potential blame, meaning that in cases where the agent who was ascribed responsibility did not achieve the expected result, we are likely to blame her. Vision Zero still ascribes backward-looking responsibility and to some degree forward-looking responsibility to individuals, but adds the explicit forward-looking responsibility of the system designers.

Accidents, Traffic↗
PubMed2005

Partial perceptual equivalence between vision and touch for texture information.

The present study examined the extent to which vision and touch are perceptually equivalent for texture information in adults. Using Garbin's method, we selected two sets of textures having high versus low cross-modal dissimilarity values between vision and touch (Experiment 1). The two sets of textures were then used as material in a cross-modal matching task (Experiment 2). Results showed that asymmetries occurred in the performances when the stimuli had high cross-modal dissimilarity values, but not when the stimuli had low cross-modal dissimilarity values. These results extend Garbin's findings on shape information to the texture domain and support the idea that partial perceptual equivalence exists between vision and touch.

Adult↗
PubMed2006

The effect of decreased visual acuity on clinical color vision testing.

PURPOSE: Evaluate the effect of visual acuity on color vision testing. DESIGN: University based clinical experimental study. METHODS: Right eyes of 12 healthy subjects were fogged with plus lenses to logMAR 1.88 and assessed with D-15 panel, Ishihara, and Hardy-Rand-Rittler (HRR) plates. Subjects were tested at lesser degrees of fogging, 0.1 logMAR intervals. The acuity at which 5% of the population tests abnormally was estimated as follows. The average acuity at which a 10% reduction in correct responses occurred was determined. From this, two standard deviations were subtracted. Examination devices were compared using repeated measures analysis of variance. RESULTS: Color vision testing did not significantly differ from baseline up to logMAR 1.40 (D-15 panel), 1.10 (HRR plates), and 0.72 (Ishihara plates). Testing devices were significantly different (P < .005). CONCLUSIONS: Color vision testing is accurate up to logMAR 1.40 (20/501) with D-15 panel, 1.10 (20/252) with HRR plates, and 0.72 (20/106) with Ishihara plates.

Adult↗
PubMed2006

Predicting patients' night vision complaints with wavefront technology.

PURPOSE: To evaluate the accuracy of the diagnostic capabilities of optical metrics generated from wavefront measurements in relationship to post-laser-assisted in situ keratomileusis (LASIK) visual complaints as expressed and drawn by patients. DESIGN: Retrospective analysis and observational case series. METHODS: Patient wavefront data from an investigational device exemption study for wavefront-guided ablations were used to derive normative modulation transfer function (MTF), encircled energy (EE), and Strehl ratio. These optical metrics and their point-spread functions (PSF) were compared with data from five postoperative patients with night vision complaints. Patients were asked to draw their symptoms, which were elicited by testing with a Fenthoff muscle light, while using their best-corrected distance vision. RESULTS: The MTF, EE, and Strehl ratio of most patients were markedly different from those of the averages of 208 normal myopic eyes before and after LASIK surgery. The spatial extent of the PSF correlated positively with the severity of the visual complaints. Wavefront-derived PSFs were markedly similar to the patients' drawings. CONCLUSIONS: The results of this study demonstrate the diagnostic capability of the wavefront system in predicting visual symptoms and complaints of patients with high-order aberrations. Objective visual metrics from patients with night vision complaints were different from those of normal myopic eyes that had undergone LASIK procedures.

Adult↗
PubMed2005

Video-assisted surgery represents more than a loss of three-dimensional vision.

BACKGROUND: Loss of depth cues is a major challenge facing surgeons performing video-assisted surgery (VAS). Whether the degradation of image quality from a video-displayed image plays a direct role in performance of VAS has not been studied. METHODS: Twenty-four volunteer novice subjects were randomized to binocular direct-vision (BDV), monocular direct-vision (MDV), or video-imaging (VI) conditions. Each subject completed ten trials of a simple cutting task in a box trainer using standard laparoscopic instruments. RESULTS: VI subjects made significantly fewer correct incisions than both of the other groups for all trials. Differences between the BDV and MDV groups did not reach statistical significance. Improvement in performance was more rapid in the BDV group than in either the MDV or VI groups. CONCLUSIONS: The degradation of image quality with VI has a detrimental influence on VAS performance above and beyond the loss of binocular vision.

Adult↗
PubMed2005

Coronary artery disease and risk factors in people with posttraumatic vision loss.

OBJECTIVE: To examine the prevalence of coronary artery disease (CAD) and its risk factors in people with posttraumatic vision loss (PTVL). DESIGN: Cross-sectional, controlled study. SETTING: The general community. PARTICIPANTS: Study groups included 82 subjects with PTVL, 49 siblings, 58 blind subjects with retinitis pigmentosa (RP), and the general population in Israel. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Sociodemographic and biomedical data collected by using a structured questionnaire and medical records. RESULTS: The prevalence of CAD among subjects with PTVL (24%) was 2 to 3 times higher than the control groups ( P <.001). However, the prevalence of the CAD risk factors in these subjects was similar to or lower than those in the control groups. For example, significantly fewer subjects with PTVL were physically inactive (16%) than patients with RP (55%, P <.01). The only variable that was significantly associated with CAD prevalence was the cause of blindness-that is, trauma versus disease; the odds of having CAD after traumatic vision loss was 3.75 times higher than after RP. CONCLUSIONS: People with PTVL exhibit elevated rates of risk for CAD similar to those of other groups with physical disability. The traumatic injury that caused vision loss might be an important factor underlying that risk.

Adult↗
PubMed2006

Loss of vision as a presenting sign of cobalamin deficiency: An eye-opener.

We describe a patient who presented with loss of vision that turned out to be caused by cobalamin deficiency. Both her vision and her visual field improved upon supplementation of cobalamin. It is, therefore, important to consider cobalamin deficiency as a treatable cause of loss of vision.

Journal Article↗
PubMedDate not supplied

A comparison of neural computations underlying stereo vision and sound localization.

Stereo vision and sound localization are behaviors that help organisms to orient in space. Stereo vision provides information about the distance of an object. In sound localization mainly directional signals are analyzed. Two specific cues, binocular disparities underlying stereo vision, and the interaural time difference, suited to represent azimuth in sound localization, have many computational problems in common, although they are generated in two different modalities. The extraction of both cues requires a comparison of signals that arise from two independent sensors, called two-sensor comparison here. This two-sensor comparison is achieved by algorithms similar to summation, half-wave rectification and multiplication. Since the underlying neurons are band-pass filters, the two-sensor comparison results in ambiguities. These are removed in a hierarchical way in several computational steps, involving squaring, inhibition and across-frequency integration.

Animals↗