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At least 289 records · Page 16Linked to original sources
PubMed2000

Role of perceptual organization in chromatic induction.

Color matches between two small patches were made in a display containing ten larger regions of different chromaticities. The spatial organization of the ten regions was varied while keeping constant the immediate surround of each patch as well as the space-average chromaticity of the entire stimulus. Different spatial arrangements were designed to alter the perceptual organization inferred by the observer without changing the ensemble of chromaticities actually in view. For example, one arrangement of the ten regions was consistent with five surfaces under two distinct illuminations, with one edge within the display (an "apparent illumination edge") dividing the stimulus into two areas, one under illuminant A and the other under illuminant C. Another spatial arrangement had the ten regions configured to induce an observer to infer ten surfaces under a single illumination. When the ten regions were arranged with an apparent illumination edge, the patch within the area of illuminant C was perceived as bluer than when the same patch and immediate surround were presented without an apparent illumination edge. The results are accounted for by positing that observers group together regions sharing the same inferred illumination, with a consequent effect on color perception: A fixed patch-within-surround shifts in hue and saturation toward the perceived illumination. We suggest that the change in color perception in a complex scene that results from a difference in real illumination may be caused by the inferred illumination at the perceptual level, not directly by the physical change in the light absorbed by photoreceptors.

Adult↗
PubMed1997

Evaluation of agreement among dermatologists in the assessment of the color of port wine stains and their clearance after treatment with the flashlamp-pumped dye laser.

BACKGROUND: Color classification and its subjective clearance evaluation in response to treatment are essential in the management of patients with port wine stains (PWS). But color perception by physicians is not an objective measurement so that it can change among observers. Agreement among physicians is essential for the reliability of the color classification and the clinical assessment of the response to laser treatment. OBJECTIVE: The purpose of our study was to determine the reliability of the clinical color classification of port wine stains and of their color change or clearance in response to laser treatment. The study was not designed to evaluate the outcome of laser treatment in PWS or the factors that could predict the final response. METHODS: We used the kappa index to evaluate the proportion of agreement in color and clearance perception among dermatologists. Six dermatologists classified the initial color of PWS in 80 patients. Three of them also assessed the amount of clearance achieved after treatment with the flashlamp-pumped dye laser. These three dermatologists were usually dedicated to treat patients with PWS, while the other three were not. RESULTS: The kappa index showed a substantial agreement in both cases. No difference in the initial color perception was observed between the group of dermatologists specialized in PWS and the other three dermatologists. CONCLUSION: These results favor the reliability of the clinical method in the assessment of PWS before and after laser treatment. So, although subjective, color perception by physicians can be used in the study of laser treatment outcome in PWS and its related factors, and the results of different authors can be compared.

Color↗
PubMed2000

Computer-based training of stimulus detection improves color and simple pattern recognition in the defective field of hemianopic subjects.

In a previously conducted randomized placebo-controlled trial, we were able to demonstrate significant visual field enlargement induced by restitution therapy in patients with cerebral lesions [Kasten, E., Wuest, S., Behrens-Bamann, W., & Sabel, B. A. (1998c). Computer-based training for the treatment of partial blindness. Nature Medicine, 4, 1083-1087.]. Visual field training was performed on a computer monitor for 1 hr per day over a period of 6 months. Since the procedure included only stimulation with white light, in the present study we investigated if this simple detection training had a transfer effect on color or form recognition in the trained area (i.e., in the absence of modality specific training). Answering this question would be crucial for planning optimal restitution therapy: In case there is no transfer of training effects to other visual modalities, a specific treatment of each visual function must be performed in order to achieve maximum benefit. Therefore, we analyzed the data from 32 patients with visual field defects who had participated in the original trial and whose form and color recognition had been investigated. The experimental group (n = 19, restitution training) experienced not only an increase of 12.8% correctly detected stimuli (PeriMa program, p <.05), but also an improvement of 5.6% in pattern recognition (PeriForm) and of 6.1% in color perception (PeriColor), respectively. In contrast, the placebo group (n = 13, fixation training) showed no significant changes from baseline to final outcome in any of the visual modalities (PeriMa: 0.3%; PeriForm: -0.3%; PeriColor: 0.4%). Conventional perimetry yielded an increase of 7.8% detected stimuli in the experimental group, but only of 1.2% in the placebo group (p <.05). For form recognition and color perception, the differences between the results of the experimental and the placebo groups narrowly missed significance. However, correlations of diagnostic results showed that mainly those patients who had achieved visual field enlargement also improved in color and form perception: r =.67 (p <.05) between PeriMa and PeriForm and r =.32 between PeriMa and PeriColor. We conclude that visual restitution training using a simple white light stimulus has at least some influence on improving other visual functions such as color and pattern recognition. This result supports the "bottleneck theory" of visual restitution, i.e., training effects can be explained as a process of perceptual learning and increased processing of information by residual structures surviving lesions of the primary visual pathways.

Audiovisual Aids↗
PubMed2000

Perception and the conditioning reflex: vector encoding.

Color perception is dependent on the generation of an excitation vector which, acting on a pool of color detectors (color detector map), produces a corresponding sensation. The generation of the color excitation vector starts at the retinal level, proceeds in the lateral geniculate body, and reaches color detectors at the cortical level. Following processing at the level of declarative memory and semantic maps, results in a verbal categorization of colors. Parallel to the excitation vector pathway, a network computing color differences is operating. The computation of color differences at the retinal level possibly takes place in phasic bipolar cells and progresses in the lateral geniculate body and at the cortical level. Detectors of color differences are assumed to be a basis of respective numerical estimations in humans. Data from frogs, fish, monkeys and humans are compared.

Animals↗
PubMed2002

Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words.

In 'colored-hearing' synesthesia, individuals report color experiences when they hear spoken words. If the synesthetic color experience resembles that of normal color perception, one would predict activation of parts of the visual system specialized for such perception, namely the human 'color center', referred to as either V4 or V8. Using functional magnetic resonance imaging (fMRI), we here locate the region activated by speech in synesthetes to area V4/V8 in the left hemisphere, and demonstrate overlap with V4/V8 activation in normal controls in response to color. No activity was detected in areas V1 or V2, suggesting that activity in primary visual cortex is not necessary for such experience. Control subjects showed no activity in V4/V8 when imagining colors in response to spoken words, despite overtraining on word-color associations similar to those spontaneously reported by synesthetes.

Adult↗
PubMed1972

Motion perception: a color-contingent aftereffect.

When observers who watched repeated alternations of a red contracting spiral and green expanding spiral were later shown stationary spirals, red and a green the red stationary spiral appeared to be expanding and the green stationary spiral appeared to be contracting. These color-contingent motion after effects complement reports of motion-contingent color aftereffects and suggest that both may reflect adaptation of detectors specific to color and motion.

Adolescent↗
PubMed2001

Perception of forbidden colors in retinally stabilized equiluminant images: an indication of softwired cortical color opponency?

In color theory and perceptual practice, two color naming combinations are forbidden-reddish greens and bluish yellows-however, when multicolored images are stabilized on the retina, their borders fade and filling-in mechanisms can create forbidden colors. The sole report of such events found that only some observers saw forbidden colors, while others saw illusory multicolored patterns. We found that when colors were equiluminant, subjects saw reddish greens, bluish yellows, or a multistable spatial color exchange (an entirely novel perceptual phenomena); when the colors were nonequiluminant, subjects saw spurious pattern formation. To make sense of color opponency violations, we created a soft-wired model of cortical color opponency (based on winner-take-all competition) whose opponency can be disabled.

Color Perception↗
PubMedDate not supplied

[Trichromatic model of the constant perception of the color of objects].

A description is presented of a trichromatic model of colour constancy (MCC) of objects with concavities: folds, holes and so on. MCC involves the system of algorithmically independent processing blocks of the image heterarchically interacting and creating at its outlet a triparametric estimation of surface reflectance of each object of the picture. This estimation little depends on changes in the illumination colour. Results are presented and discussed of a computer experiment with MCC simulating the scene in which a plane with differently coloured regions and a conic hole in each are illuminated with a single chromatic light source.

Algorithms↗
PubMed1980

[Follow-up study of macular function after retinal detachment surgery (author's transl)].

Forty patients successfully operated on for retinal detachment involving the macula were followed up for periods ranging from six months to nine years. The follow-up examination included testing for visual acuity, color perception and metamorphopsias, as well as biomicroscopy and fluorescein angiography. Postoperative visual acuity was correlated with the preoperative duration of retinal detachment. As expected, visual outcome was reduced in cases with lesions demonstrated by biomicroscopy and/or fluorescein angiography. In some patients visual acuity and color perception were impaired and metamorphopsias were present, even though the macula appeared normal in funduscopy and fluorescein angiography. This may be due to a possible misalignement of the photoreceptors as demonstrated in the owl monkey by Machemer.

Adult↗
PubMed1999

Color, consciousness, and the isomorphism constraint.

The relations among consciousness, brain behavior, and scientific explanation are explored in the domain of color perception. Current scientific knowledge about color similarity, color composition, dimensional structure, unique colors, and color categories is used to assess Locke's "inverted spectrum argument" about the undetectability of color transformations. A symmetry analysis of color space shows that the literal interpretation of this argument--reversing the experience of a rainbow--would not work. Three other color to color transformations might work, however, depending on the relevance of certain color categories. The approach is then generalized to examine behavioral detection of arbitrary differences in color experiences, leading to the formulation of a principled distinction, called the "isomorphism constraint," between what can and cannot be determined about the nature of color experience by objective behavioral means. Finally, the prospects for achieving a biologically based explanation of color experience below the level of isomorphism are considered in light of the limitations of behavioral methods. Within-subject designs using biological interventions hold the greatest promise for scientific progress on consciousness, but objective knowledge of another person's experience appears impossible. The implications of these arguments for functionalism are discussed.

Color↗
PubMed1979

Blue field entoptic phenomenon in cataract patients.

The blue field entoptic phenomenon (BFE), which allows the observation of one's own leukocytes flowing in macular retinal capillaries, was used to predict postoperative macular function in 136 consecutive patients undergoing uncomplicated cataract operation. The results were compared to those obtained with three commonly used tests: two-light discrimination, color perception, and the Purkinje vascular entoptic phenomenon. All four tests identified a nearly equal number of the good maculae (visual acuity 20/40 of better) ranging from 87% for the two-light discrimination test to 94% for the BFE test. However, the tests varied greatly in predicting poor macular function (visual acuity 20/50 or worse). The BFE test identified more than 75% of the poor maculae; the Purkinje vascular entoptic test and the two-light discrimination test, only 22%; and the color perception test, 11%. A positive response to the BFE test indicated a .98 probability of good macular function; a negative response indicated a .82 probability of poor macular function, predictions that were better than the other three tests or their combination.

Cataract↗
PubMed1976

Polymorphism of human color vision.

The genetic polymorphism of human color vision is examined within the framework of a photopigment replacement model. An analysis of the X-linked recessive dichromacies and anomalous trichromacies indicates that one source of variability of normal color perception may be the inclusion of several distinct phenotypes in what is usually described as normal color vision. This analysis also reveals the cause of the dominance hierarchy at the protan and deutan loci, the perceptual effects of dosage compensation, and the phenotypes of various compound hemizygotes.

Alleles↗
PubMed1975

Color and form perception on the Rorschach as a function of eye color.

Recent research had demonstrated that dark-eyed individuals are more reactive than light-eyed people. The present paper investigated one area of reactivity, ease of emotional arousal. The hypothesis that dark-eyed male subjects (n equals 40) would show greater ease of arousal than light-eyed male subjects (n equals 40) was tested using color and form responses on the Rorschach as dependent measures. The predicted interaction was significant; light-eyed subjects gave relatively more form responses, but dark-eyed subjects gave relatively more color responses. Implications for future research and application were discussed.

Arousal↗
PubMed1992

A bidimensional theory of achromatic color vision.

The theory is based on a perceptive color system where the achromatic colors are specified by their degree of similarity to the three qualities white, black and luminous. Black and luminous are treated as opponent variables. It is assumed that white and luminous/black are determined by different kinds of visual processes termed the w- and the b-process. The relationship between these processes and luminance parameters in a simple disc/ring configuration is derived from available data. The b-process is related to stimulus contrast in a simple manner. It is assumed to involve cells with antagonistic center/surround organization of the receptive field. The w-process is primarily determined by the local luminance, and it is assumed to involve cells that lack a center/surround organization of the receptive field. The w-process has properties similar to the processes involved in chromatic color vision. The theory can account for different kinds of psychophysical data on achromatic colors like data on simultaneous contrast, color scaling, and color constancy.

Color Perception↗