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At least 1,747 records · Page 97Linked to original sources
PubMed2006

Activation of the blue opsin gene in cone photoreceptor development by retinoid-related orphan receptor beta.

Color vision requires the expression of opsin photopigments with different wavelength sensitivities in retinal cone photoreceptors. The basic color visual system of mammals is dichromatic, involving differential expression in the cone population of two opsins with sensitivity to short (S, blue) or medium (M, green) wavelengths. However, little is known of the factors that directly activate these opsin genes and thereby contribute to the S or M opsin identity of the cone. We report that the orphan nuclear receptor RORbeta (retinoid-related orphan receptor beta) activates the S opsin gene (Opn1sw) through binding sites upstream of the gene. RORbeta lacks a known physiological ligand and activates the Opn1sw promoter modestly alone but strongly in synergy with the retinal cone-rod homeobox factor (CRX), suggesting a cooperative means of enhancing RORbeta activity. Comparison of wild-type and mutant lacZ reporter transgenes showed that the RORbeta-binding sites in Opn1sw are required for expression in mouse retina. RORbeta-deficient mice fail to induce S opsin appropriately during postnatal cone development. Photoreceptors in these mice also lack outer segments, indicating additional functions for RORbeta in photoreceptor morphological maturation. The results identify Opn1sw as a target gene for RORbeta and suggest a key role for RORbeta in regulating opsin expression in the color visual system.

Animals↗
PubMed1986

The detection of various color combinations under different chromatic ambient illuminations.

Our purpose was to reveal the effects of ambient illumination color and various foreground/background color pairings on a choice reaction time task performed on a color CRT. Six men and two women with normal color vision served as observers in a four-alternative forced choice procedure. A small (18' visual angle) colored circle appeared in the center of one of the unmarked quadrants of the screen. The observer's task was to respond as quickly as possible to this target by pressing one of four buttons corresponding to its location. We found that target colors that were opponent to the background colors were most quickly detected. Detection was enhanced by maximizing both brightness and chromatic contrast, but brightness contrast was much more effective. Chromatic ambient lighting which was a log unit dimmer than the target luminance had no effect on performance.

Choice Behavior↗
PubMed1993

Natural history and visual outcome in patients with APMPPE.

We undertook a retrospective study of the files of 21 patients (42 affected eyes) with acute posterior multifocal placoid pigment epitheliopathy to obtain details on the natural history of the disease and on the functional and visual outcome (mean follow up: 17 months). The final visual acuities were 8/10 or better in 34 eyes (81.0%), 7/10 to 2/10 in 6 eyes (14.2%) and 1/10 in two eyes (4.8%). Although the final visual acuity was good in most eyes, 24 eyes (57.2%) were still symptomatic due to scotomas (33.3%), metamorphosia (21.4%), decreased vision (16.6%), floaters (4.8%) and chronic redness (2.4%). Recurrences did not occur in this group of patients. Electrophysiological and color vision tests were performed in the initial phase of the disease, but we found no correlation between the test results and the final visual acuity.

Adolescent↗
PubMed1989

Evaluation of the functional results after different techniques for treatment of retinal detachment due to macular holes.

A total of 50 eyes with retinal detachment due to macular holes were treated in the period from July 1986 to December 1987. In all, 10 eyes underwent pneumatic retinopexy using plain room air. A total of 30 eyes were treated by pars plana vitrectomy, followed by fluid/air exchange, with no treatment of the macular break; in 9 of these the detachment recurred, reflattening of the retina by air tamponade followed by laser photo-coagulation. The other 10 eyes underwent pars plana vitrectomy followed by silicone oil tamponading because of proliferative vitreoretinopathy (PVR). This paper compares the functional results for each group. The parameters used included visual acuity, color vision and visual fields.

Adult↗
PubMed1981

Chromatic adaption and the fundamental stimuli.

A bipartite adaption stimulus with a horizontal dividing line adapted the upper half of the retina to red or yellow light and the lower half to white light. Monochromatic test stimuli between 460 and 520 nm were presented to the red or yellow adapted portion of the retina. After desaturating the test stimulus with red light, it was possible to match it to a mixture of 458 and 520 nm. From these data one can plot on a mixture diagram the shifts in color produced by the two kinds of adaption. The data support a zone theory of color vision similar to that proposed by Adams.

Adaptation, Ocular↗
PubMed2006

Cross-species differences in color categorization.

Berlin and Kay (1969) found systematic restrictions in the color terms of the world's languages and were inclined to look to the primate visual system for their origin. Because the visual system does not provide adequate neurophysiological discontinuities to supply natural color category boundaries, and because recent evidence points to a linguistic origin (Davidoff, Davies, & Roberson, 1999), a new approach was used to investigate the controversial issue of the origin of color categories. Baboons and humans were given the same task of matching-to-sample colors that crossed the blue/green boundary. The data and consequent modeling were remarkably clear-cut. All human subjects matched our generalization probe stimuli as if to a sharp boundary close to the midpoint between their training items. Despite good color discrimination, none of the baboons showed any inclination to match to a single boundary but rather responded with two boundaries close to the training stimuli. The data give no support to the claim that color categories are explicitly instantiated in the primate color vision system.

Adult↗
PubMed2025

Tandem Gene Clusters as Phylogenetic Anchors Reveal the Hidden History of Vertebrate Visual Opsins.

The expansion of the visual opsin gene family was a crucial event in the diversification of vertebrate vision in evolution. Additional expansions in phototransduction-related genes facilitated the development of dim-light (rods) and color vision (cones). Sequence-based phylogeny and gene positions from extant jawed vertebrate genomes are insufficient to untangle the visual opsin duplications in early vertebrates. Additionally, jawless vertebrates share a visual opsin gene repertoire with jawed vertebrates which conflicts with recent findings of distinct whole-genome duplications in each lineage. To resolve these questions, we analyzed jawless vertebrate genomes, focusing on visual opsin genes. Our findings, based on chromosomal arrangements and relationships, confirm tandem duplications of visual opsins before the vertebrate radiation.

Animals↗
PubMed2006

Physiological basis for cochlear and auditory brainstem implants.

Cochlear implants bypass functions of the cochlea that have been regarded to be fundamental for discrimination of the frequency (or spectrum). Frequency discrimination is essential for discrimination of sounds, including speech sounds, and the normal auditory system is assumed to make use of both (power) spectral and temporal information for frequency discrimination. Spectral information is represented by the place on the basilar membrane that generates the largest amplitude of vibration on the basilar membrane. Evidence has been presented that the temporal representation of frequency is more robust than the place representation and thus regarded more important for speech discrimination. The fact that some cochlear implants provide good speech discrimination using only information about the energy in a few spectral bands seems to contradict these studies. In that way, frequency discrimination may be similar to trichromatic color vision, which is based on the energy in only three different spectral bands of light, accomplished by different color-sensitive pigments in the cones of the retina. Cochlear nucleus implants (ABIs) also bypass the auditory nerve, which does not perform any processing. Therefore, it may be expected that ABIs are equally efficient as cochlear implants. However, experience from the use of ABIs in patients with bilateral vestibular schwannoma has not been encouraging, but recent studies of the use of ABIs in patients with other causes of injuries to the auditory nerve have shown similar speech discrimination as achieved with modern cochlear implants. Cochlear implants and ABIs are successful in providing speech discrimination because of redundancy in the processing in the ear, redundancy of the speech signal and because the auditory nervous system has a high degree of plasticity. Expression of neural plasticity makes the auditory nervous system adapt to the change in demands of processing of the information provided by cochlear implants.

Auditory Brain Stem Implants↗
PubMed1995

IPS Classic. Science, art and nature: a case report.

The ceramo-metal restoration still forms the backbone of modern restorative dentistry, despite many new systems. This article discusses a unique ceramo-metal system, its advantages, and clinical and technical applications; teamwork between the dentist and the technician is emphasized. IPS Classic (Ivoclar Williams) is a ceramic system with several exclusive features. It encompasses Color Visions, a computer-generated shade system, and the IPS Impulse modifier system allows the ceramist unlimited creativity in color development.

Aluminum Silicates↗
PubMed1995

Science, art and nature: a case report.

The ceramo-metal restoration still forms the backbone of modern restorative dentistry, despite many new systems. This article discusses a unique ceramo-metal system, its advantages, and clinical and technical applications teamwork between the dentist and the technician is emphasized. IPS Classic (Ivoclar Williams) is a ceramic system with several exclusive features. It encompasses Color Visions, a computer-generated shade system, and the IPS Impulse modifier system allows the ceramist unlimited creativity in color development.

Dental Porcelain↗
PubMed1997

Hue scaling of isoluminant and cone-specific lights.

Using a hue scaling technique, we have examined the appearance of colored spots produced by shifts from white to isoluminant stimuli along various color vectors in order to examine color appearance without the complications of the combined luminance and chromatic stimulation involved in most previous hue scaling studies, which have used flashes of monochromatic light. We also used spots lying along cone-isolating vectors in order to determine what hues would be reported with a change in activation of only single cone types or of only single geniculate opponent-cell types, an issue of direct relevance to any model of color vision. We find that: 1. Unique hues do not correspond either to the change in activation of single cone types or of single geniculate opponent-cell types. This is well known to be the case for yellow and blue, but we find it to be true for red and green as well. 2. These conclusions are not limited to the particular white (Illuminant C) used as an adapting background in most of the experiments. Shifts along the same cone-contrast vectors relative to different backgrounds lead to much the same hue percepts, independent of the starting white used. 3. The shifts of the perceptual colors from the geniculate axes are in the directions, and close to the absolute amounts, predicted by our [De Valois & De Valois (1993). Vision Research, 33, 1053-1065] multi-stage color model in which we postulate that the S-opponent cells are added to or subtracted from the M- and L-opponent cells to form the four perceptual color systems. 4. There are distinct asymmetries with respect to the extent to which various hues within each perceptual opponent system deviate from the geniculate opponent-cell axes. Blue is shifted more from the S-LM axis than is yellow; green is shifted more from the L-M axis than is red. There are also asymmetries in the angular extent of opponent color regions. Blue is seen over a larger range of color vectors than is yellow, and red over a slightly larger range than green. 5. Such asymmetries are not accounted for by any model that treats red-green and yellow-blue each as unitary, mirror-image opponent-color systems. Although red and green are perceptually opponent, the red and green perceptual systems do not appear to be constructed in a mirror-image fashion with respect to input from different cone types or from different geniculate opponent-cell types. The same is true for yellow and blue.

Color Perception↗
PubMed1985

Two temporal phases, brightness-dependent and -independent, in the chromatic response elicited by a briefly-flashed monochromatic light: a preliminary report.

The strength of chromatic response elicited by a briefly-flashed monochromatic light, which varied in its exposure duration, was measured with the "transient cancellation method" in Experiment 1. It was found that the chromatic response of a test color depended on brightness of the test field, up to the exposures of 100-200 msec. But it began to decrease, independent of brightness of the field, at the longer durations. The above results were confirmed by Experiment 2, in which the perceived saturation of a colored light was estimated with the two alternative forced choice method. Those results were tentatively interpreted as indicating the two kinds of chromatic responses presumably originating at the different stages in the visual system. Some other psychophysical dada on color vision were briefly referred to in relation to the present results.

Color Perception↗
PubMed2001

Nonlocal interactions in color perception: nonlinear processing of chromatic signals from remote inducers.

The perceived color of an object depends on the chromaticity of its immediate background. But color appearance is also influenced by remote chromaticities. To quantify these influences, the effects of remote color fields on the appearance of a fixated 2 degrees test field were measured using a forced-choice method. Changes in the appearance of the test field were induced by chromaticity changes of the background and of 2 degrees color fields not adjacent to the test field. The appearance changes induced by the color of the background corresponded to a fraction of between 0.5 and 0.95 of the cone contrast of the background change, depending on the observer. The magnitude of induction by the background color was modulated on average by 7.6% by chromaticity changes in the remote color fields. Chromaticity changes in the remote fields had virtually no inducing effect when they occurred without a change in background color. The spatial range of these chromatic interactions extended over at least 10 degrees from the fovea. They were established within the first few hundred milliseconds after the change of background color and depended only weakly on the number of inducing fields. These results may be interpreted as reflecting rapid chromatic interactions that support robustness of color vision under changing viewing conditions.

Color Perception↗
PubMed2002

Opsin gene and photopigment polymorphism in a prosimian primate.

A recent genetic investigation found some species of prosimian to have an opsin gene polymorphism [Nature 402 (1999) 36]. In the present study the functional implications of this finding were explored in a correlated investigation of opsin genes and spectral sensitivity measurements of a diurnal prosimian, Coquerel's sifaka (Propithecus verreauxi coquereli). Spectra recorded using electroretinogram (ERG) flicker photometry reveal a cone photopigment polymorphism paralleling an opsin gene polymorphism detected by molecular methods. This species has two middle-to-long-wavelength cone pigments with peak sensitivities of about 545 and 558 nm and a short-wavelength-sensitive cone with a peak at about 430 nm. The distribution of these pigments among animals predicts the presence of both dichromatic and trichromatic forms of color vision.

Animals↗
PubMed2003

Quality of life in glaucoma and its relationship with visual function.

PURPOSE: The aims of this study were (a) to explore patients self-reported visual disability resulting from glaucoma by means of a questionnaire developed for this purpose; (b) identify activities strongly associated with a measure of visual field loss, (c) to quantify different psychophysical aspects of visual function; (d) to assess the relationship between objective measures of visual function and patients' perception of their vision-related quality of life. PATIENTS AND METHODS: Three groups of glaucoma patients (n = 47) with mild (n = 18), moderate (n = 19), and severe visual field loss (n = 10) and a group of normal controls (n = 19) underwent a comprehensive clinical examination, completed a questionnaire and, on a separate visit, performed a number of psychophysical tests of visual function. MAIN OUTCOME MEASURES: Questionnaire responses (vision-related quality of life, general health and psychosocial variables), visual acuity, visual fields, Esterman binocular disability scores, contrast sensitivity, critical flicker frequency, color vision, dark adaptation, glare disability (brightness acuity), and stereoacuity scores were measured. RESULTS: Fifteen of the 50 questions were noted to have a strong significant relationship with a measure of visual field loss and were included in a new questionnaire scale, the Glaucoma Quality of Life - 15 (GQL-15). The scale validity showed a significant correlation with perimetric mean deviation (MD) values (r = -0.6; P < 0.0001), the reliability of the scale was high (Cronbach alpha = 0.95), and test-retest reliability of the questionnaire was strong (r = 0.87). An overall statistically significant decrease in performance-related quality of life was noted between normal subjects and all groups of glaucoma patients. A significant relationship was found between the scale questionnaire summary performance measure and a number of psychophysical tests: Pelli-Robson contrast sensitivity (r = -0.45, P < 0.001), glare disability (r = -0.41, P < 0.001), Esterman binocular visual field test (r = -0.39, P < 0.001), dark adaptation (r = 0.34, P = 0.007), and stereopsis (r = 0.26, P = 0.04). CONCLUSION: Perceived visual disability relating to certain tasks (particularly involving dark adaptation and disability glare, activities demanding functional peripheral vision such us tripping over and bumping into objects and outdoor mobility tasks) was significantly associated with the severity of binocular visual field loss. As a result, a new glaucoma-specific questionnaire scale with good performance characteristics is presented in this study. The difficulties encountered by patients in everyday life (as measured with the questionnaire) were also mirrored in their performance on a number of psychophysical tests, especially contrast sensitivity, glare disability, Esterman binocular visual field test, and dark adaptation.

Aged↗
PubMed2002

Color constancy and the functional significance of McCollough effects.

A central problem in visual perception concerns how humans perceive stable and uniform object colors despite variable lighting conditions (i.e. color constancy). One solution is to 'discount' variations in lighting across object surfaces by encoding color contrasts, and utilize this information to 'fill in' properties of the entire object surface. Implicit in this solution is the caveat that the color contrasts defining object boundaries must be distinguished from the spurious color fringes that occur naturally along luminance-defined edges in the retinal image (i.e. optical chromatic aberration). In the present paper, we propose that the neural machinery underlying color constancy is complemented by an 'error-correction' procedure which compensates for chromatic aberration, and suggest that error-correction may be linked functionally to the experimentally induced illusory colored aftereffects known as McCollough effects (MEs). To test these proposals, we develop a neural network model which incorporates many of the receptive-field (RF) profiles of neurons in primate color vision. The model is composed of two parallel processing streams which encode complementary sets of stimulus features: one stream encodes color contrasts to facilitate filling-in and color constancy; the other stream selectively encodes (spurious) color fringes at luminance boundaries, and learns to inhibit the filling-in of these colors within the first stream. Computer simulations of the model illustrate how complementary color-spatial interactions between error-correction and filling-in operations (a) facilitate color constancy, (b) reveal functional links between color constancy and the ME, and (c) reconcile previously reported anomalies in the local (edge) and global (spreading) properties of the ME. We discuss the broader implications of these findings by considering the complementary functional roles performed by RFs mediating color-spatial interactions in the primate visual system.

Animals↗