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PubMed1995

Color appearance with sparse chromatic context.

We compared changes in the appearance of a test region caused by introducing an inhomogeneous chromatic background to changes caused by a space-averaged equivalent uniform background. Subjects adjusted a test field presented on a CRT so that it appeared neither reddish nor greenish. Sparse "white" or "green" dots, randomly scattered throughout a "red" background field, caused a large decrease (up to 15 nm) in the dominant wavelength of the red/green equilibrium setting, compared to measurements with a uniform "red" background. A uniform background with the same space-averaged chromaticity and luminance as the complex background had an effect similar to the uniform "red" background. These results contradict theories of color constancy that rely on the "gray world" assumption, and indicate the significance for color perception of individual chromaticities within discrete, noncontiguous regions.

Adaptation, Ocular↗
PubMedDate not supplied

Electrophysiological studies of color processing in human visual cortex.

Electrophysiological recordings from human visual cortex were carried out with electrodes chronically implanted in 13 patients for localization of an epileptogenic focus. Visual evoked potentials (VEPs) elicited by red or blue checkerboard stimuli were recorded using an adaptation stimulus-test stimulus design in which color was the most salient feature. A "significant color effect," defined as a statistically significant effect of the adaptation stimulus on test stimulus VEPs evoked by the same or a different color, was determined for various cortical regions: medial lingual gyrus, 20%; lateral lingual gyrus, 38%; posterior fusiform gyrus, 50%; anterior fusiform gyrus, 0%; inferior temporal gyrus, 5%; occipital pole, 30%; lateral surface of non-visual cortex, 6%; inferior parietal and temporal cortex, 5%. The time course of the significant color effects suggests that wave length-selective neuronal activity occurs initially at the first stage of cortical processing in the medial lingual gyrus, followed by progressively later activation of the lateral lingual gyrus, the posterior fusiform gyrus, and the inferior temporal gyrus. In two patients, stimulation of the lateral lingual and fusiform gyri elicited color sensations in the contralateral half-field, whereas stimulation of the medial lingual and cuneate gyri evoked retinotopically appropriate quadrantic "shimmering" devoid of color. These results suggest that a region of inferior occipital cortex, primarily the posterior portion of the fusiform gyrus, is involved in color perception and may be homologous with area V4 in monkeys. There is also a region of dorsolateral surface cortex which exhibits a fairly high percentage of significant color effects and when stimulated may evoke sensations of color. This region may be the same as the dorsolateral region thought to be involved in selective attention to color.

Adult↗
PubMedDate not supplied

Color-coded pattern suppresses visual evoked cortical potentials and electroretinograms.

We developed a new visual stimulating system for recording visual evoked cortical potentials and electroretinograms. The stimulus was a color checkerboard, in which each check kept its chromaticity but changed its luminance with its corresponding check. Color-coded pattern stimuli using red and green checks did not produce visual evoked cortical potentials, while yellow checks produced clear responses in a normal subject. Moreover, five color stairs from red and green to yellow showed only that the more colors are different, the smaller the visual evoked cortical potentials become. In addition electroretinogram recordings indicated that color-coded patterns behave in the same way as in visual evoked cortical potentials. The mechanism that causes the small color visual evoked cortical potentials may already be present in the retina. Color perception may be able to induce a suppression of responses for luminance contrast that appears to be formed already in the retina. Retinal responses were affected whether the stimulus field was color coded or not. Pattern electroretinograms appear to be more than the sum of local on and off responses.

Adult↗
PubMed1994

Retrieval of color and form during suppression of temporal cortex with cold.

Five cryodes were implanted on each side over the dorsal aspect of inferotemporal cortex (TEd) of three monkeys. They were trained on a form discrimination and three color discriminations. Suppression of TEd with cold disrupted retrieval of the color, but not the form discriminations. The animals could find the colors in a background of shifting values of gray, indicating that the suppression did not reduce their color perception to gray. They initially had great difficulty matching red to red and green to green, although that recovered with experience. The animals tended to respond to one or the other of the colors, indicating that they could perceive and discriminate them, but, either lost information about the correct stimulus, or something from past experience was interfering with performance. We suggested that cooling TEd suppresses new and recent learning of color discriminations, but it does not suppress some previous experience that intrudes upon performance of new tasks. TEd might contain episodic information about colors necessary for performance of the immediate task.

Animals↗
PubMedDate not supplied

An fMRI version of the Farnsworth-Munsell 100-Hue test reveals multiple color-selective areas in human ventral occipitotemporal cortex.

Studies of patients with cerebral achromatopsia have suggested that ventral occipitotemporal cortex is important for color perception. We created a functional magnetic resonance imaging (fMRI) version of a clinical test commonly used to assess achromatopsia, the Farnsworth-Munsell 100-Hue test. The test required normal subjects to use color information in the visual stimulus to perform a color sequencing task. A modification of the test requiring ordering by luminance was used as a control task. Subjects were also imaged as they passively viewed colored stimuli. A limited number of areas responded more to chromatic than achromatic stimulation, including primary visual cortex. Most color-selective activity was concentrated in ventral occipitotemporal cortex. Several areas in ventral cortex were identified. The most posterior, located in posterior fusiform gyrus, corresponded to the area activated by passive viewing of colored stimuli. More anterior and medial color-selective areas were located in the collateral sulcus and fusiform gyrus. These more anterior areas were not identified in previous imaging studies which used passive viewing of colored stimuli, and were most active in our study when visual color information was behaviorally relevant, suggesting that attention influences activity in color-selective areas. The fMRI version of the Farnsworth-Munsell test may be useful in the study of achromatopsia.

Adaptation, Physiological↗
PubMed1991

Shade color discrimination by men and women.

Women have traditionally been believed to be more capable of matching colors than men. Because of this factor women should tend to agree with one another more often than men regarding tooth shade selection. This study tested differences in dental color perception between men and women. Six women and six men, all dental students, were selected and given the Farnsworth-Munsell 100 Hue test and the Farnsworth D15 test to rule out any inherent color deficiences. The students then used three different shade guides and three different light sources to match each others' teeth. Students selected shades for the gingival third and incisal third sites of selected maxillary anterior teeth. The students rotated use of the different shade guides and light sources. Descriptive statistics and ANOVA were performed on the data. Generally, there were no statistically significant findings with the use of three light sources and two shade guides for men at the p less than 0.05 level. For women, the light source made a difference. The men, as a group, showed borderline more (63% to 58%) uniform shade selection than the women.

Adult↗
PubMed1979

Effects of pseudoephedrine and triprolidine on visual performance.

The effects of q.i.d. administration of 60 mg pseudoephedrine (Sudafed) tablets or pseudoephedrine-triprolidine (Actifed) tablets after 5 d of medication were measured on tests of night vision, color perception, stereopsis, and reaction time. Neither drug appeared to impair performance.

Color Perception↗
PubMed1989

A regularized approach to color constancy.

Color constancy is the ability of color perception independent of the spectrum of the ambient illumination. We present an algorithm that makes use of biologically plausible assumptions concerning the spectra of illumination and surface reflectance in order to solve the undetermined problem of color constancy. We test the proposed algorithm by means of computer simulations and examine its range of performance.

Algorithms↗
PubMed1994

Kromoscopic analysis: a possible alternative to spectroscopic analysis for noninvasive measurement of analytes in vivo.

Light that penetrates scattering media shows nonlinearities that mask the broad and shallow perturbations made by trace analytes on the background illuminant spectrum. Narrow-band spectroscopic decomposition and deconvolution of such weak bands is a formidable analytical task that pushes the fundamentally linear spectroscopic method beyond practical limits. Kromoscopy is a high-dimensional analog of human color perception; it has broad-band spectrally overlapping detectors similar to those of the visual system, but in the infrared. Analyte bands are integrated fully in two or more detectors with different relative weightings. As in color vision, the analyte information is coded in the direct correlations between detector signals, which individually have higher signal-to-noise ratios than their spectroscopic counterparts. Our Kromoscopic instrument responds directly to glucose in aqueous solution, is not affected by temperature disturbances, and is fast enough to measure physiologically induced Kromoscopic changes in the arterial pulse waveform with high precision.

Blood Glucose↗
PubMedDate not supplied

Video-endoscope versus endoscope for paranasal sinus surgery: influence on visual acuity and color discrimination.

Endoscopic and video-endoscopic visual acuity and color discrimination were investigated using a standard disk for testing visual acuity and a color discrimination test. A 1-chip-CCD-Camera (CCC) or 3-chip-CCD-Camera plus digital image processing (digivideo) on the endoscope and a 15 inch high resolution video monitor were used. Color discrimination was investigated by comparing the ability to sort colored disks of low chromatic saturation (desaturated Panel D-15 Test), ranging from yellow to red, under direct vision or via monitor using the same 1-CCC- and 3-CCC-system. Visual acuity deteriorated by 1.58 +/- 0.16 steps (+/- SEM) for the 1-CCC and 1.21 +/- 0.16 steps for the 3-CCC plus digivideo compared to vision through the endoscope (p < 0.001 and p < 0.001). Visual acuity was significantly better for the 3-CCC-video-endoscope compared to the 1-CCC-video-endoscope (p = 0.0045). The difference in color discrimination between the naked eye and the 1-CCC-monitor system was not significant. More mistakes were made with the 3-CCC-monitor system. The impairment of image quality with the video endoscope, which is experienced by many surgeons, is reflected in a marked loss of visual acuity in our experiments. Sharpness and contrast of the video-image are significantly enhanced by the 3-CCC plus digital image processing, compared to the 1-CCC. Color discrimination, however, was not impaired by the 1-CCC, indicating that color perception with the video-endoscope can be very good and may not contribute significantly to the loss of image quality.

Color Perception↗
PubMed1996

Neuronal mechanisms of color categorization in areas V1, V2 and V4 of macaque monkey visual cortex.

A landmark study conducted by Berlin and Kay (Basic Color Terms, University of California Press, Berkeley, 1969, pp. 1-12) demonstrates that well-developed languages contain exactly 11 basic color terms. The basic colors (8 chromatic and 3 achromatic) are situated in specific locations of color space, suggesting a fixed relationship between specific hue and luminance. To determine the physiologic origins of the basic colors, we have studied the responses of cells in visual cortical areas V1, V2 and V4 of the behaving macaque monkey, using chromatic and achromatic stimuli of varying luminance. A total of 569 cells (291 from V1, 205 from V2, 73 from V4) were obtained, and classified as 'B' (bright; 43-50% of the total cells in each area), 'D' (dark; 6-12% of the total), and 'B/D' (bright/dark; 27-28% of the total) color or non-color cells according to each cell's color/luminance preference in relation to the neutral gray background. About two thirds of 'B' cells in each area were color specific, whereas the proportion of color cells in 'B/D' and 'D' categories was lower. In all three areas (v1, V2, V4), color cells with preferences for midspectral colors (such as yellow, lime and green) also preferred high luminance levels, while color cells with preferences for endspectral colors (such as red and blue) responded preferentially to luminance levels closer to background. The date provide evidence for categorical color perception within the visual system, as well as providing a physiological basis for the increased saliency of endspectral contours observed at equiluminance in psychophysical studies.

Action Potentials↗
PubMed1998

Color vision deficits during laser lithotripsy using safety goggles for coumarin green or alexandrite but not with holmium:YAG laser safety goggles.

PURPOSE: Laser lithotripsy requires urologists to wear laser eye protection. Laser eye protection devices screen out specific light wavelengths and may distort color perception. This study tests whether urologists risk color confusion when wearing laser eye protection devices for laser lithotripsy. MATERIALS AND METHODS: Urologists were tested with the Farnsworth Dichotomous Test for Color Blindness (D-15) and the Farnsworth-Munsell 100-Hue Test (FM-100) without (control) and with laser eye protection devices for coumarin green, alexandrite and holmium:YAG lasers. Error scores were tabulated. The pattern of color deficits was characterized with confusion angles, confusion index (C-index), scatter index (S-index) and color axes. Laser eye protection devices were tested with spectrophotometry for spectral transmittance and optical density. RESULTS: The D-15 transposition errors (mean plus or minus standard deviation) for control, holmium:YAG, alexandrite and coumarin green laser eye protection were 0 +/- 0, 0 +/- 0, 0.3 +/- 0.5 and 6.4 +/- 1.6, respectively (p = 0.0000001). The FM-100 error scores (mean plus or minus standard deviation) were 20 +/- 15, 20 +/- 14, 91 +/- 32 and 319 +/- 69, respectively (p = 0.0001). The confusion index scores indicated a mild color confusion for the alexandrite and pronounced color confusion for the coumarin green laser eye protection. The confusion angles and scatter indexes mimicked a congenital blue-yellow deficit for coumarin green laser eye protection. Color axes showed no significant deficits for control or holmium:YAG laser eye protection in any subject, red-green axis deficits in 3 of 6 tested with alexandrite and blue-yellow axis deficits in 12 of 12 tested with coumarin green (p < 0.001). Spectrophotometry showed that laser eye protection for coumarin green blocks light less than 550 nm., alexandrite blocks light greater than 650 nm. and holmium:YAG blocks light greater than 825 nm. CONCLUSIONS: Laser eye protection for coumarin green causes pronounced blue-yellow color confusion, whereas alexandrite causes mild red-green color confusion among urologists, holmium:YAG causes no significant color confusion compared to controls. The differences are explained by laser eye protection spectrophotometry characteristics and visual physiology.

Adult↗
PubMed1992

Depth, motion, and static-flow perception at metaisoluminant color contrast.

Many experiments concerned with the role of color in depth and motion perception have applied isoluminant random-dot stereograms and cinematograms. The poor performance in the absence of luminance contrast has been associated with color-blindness of stereopsis and motion perception (Livingstone, M.S. & Hubel, D.H. (1987) J. Neurosci. 7, 3416-3468). Nevertheless, isoluminant stimuli are not fully accepted as appropriate tools in isolating central mechanisms (Logothetis, N.K., Schiller, P.H., Charles, E.R. & Hurlbert, A.C. (1990) Science 247, 214-217). In our experiments we use a broad luminance range to test whether color can contribute to a given mechanism when luminance contrast is present but has a strong "veto" effect from opposite luminance contrast, a condition we named "metaisoluminance." There is no fusion in stereopsis under polarity reversal, when only luminance information is given, and reversed-phi phenomenon is experienced for motion. As a third "matching" task, we included polarity-reversed random-dot Glass-patterns, which exhibit "static flow" and also show pattern reversal. We found that color can counteract the effects of polarity reversal by restoring stereoscopic fusion and reversed phi motion and does it with increased efficiency as the hue contrast increases. We found no such effect of color in Glass-patterns. Thus, we showed that the visual system for binocular depth and motion perception is not color-blind, although correlated hue information under metaisoluminance does not appear to yield shape perception.

Color Perception↗
PubMed1994

[Dependence of the sensitivity of the central visual field on hemoglobin-oxygen saturation].

Retinal function is very sensitive to changes in hemoglobin oxygen saturation. Characteristic ophthalmological symptoms of oxygen deficiency are: changes in color perception, visual field defect, eye flickering, reduction of visual acuity, seeing double images, defects in neural image interpretation. To test the dependency of changes in the central visual field sensitivity on different degrees of oxygen saturation, 48 probands (48 monocular tests) 20-50 years of age were examined in the altitude simulation chamber of the Aviation Medicine Institute of German Air Force at zero altitude (= 500 m) and at 10,000 ft (ca. 3,500 m height). Three types of experiments were performed: determination of abnormal quotient using a Heidelberg anomaloscope; determination of changes in color vision by saturated and disaturated panel D-15 test; determination of differences in light sensitivity for white, red, blue and green light by a threshold test using a Humphrey Field Analyzer (640) as perimeter. At zero level (500 m) hemoglobin-oxygen saturation was 97% +/- 1%. At 10,000 ft this value decreased to 83% +/- 3%. Hypoxic hypoxia caused neither significant AQ changes nor did it induce reproducible changes in color vision by the panel D-15 test. However, anoxia resulted in significant (P < 0.01) differences in light sensitivity in phototopic range.

Adult↗
PubMed1993

Positron-emission tomographic localization of abnormalities of brain metabolism in patients with minimal hepatic encephalopathy.

Many patients with compensated cirrhosis without overt hepatic encephalopathy have deficits in visual-spatial perception, a condition we call minimal hepatic encephalopathy. Five patients with alcohol-induced cirrhosis and nine control subjects underwent positron-emission tomographic imaging of the brain with 18F-fluorodeoxyglucose. Patients also underwent neuropsychological and clinical chemistry tests. The patients had mild arterial hyperammonemia (62 +/- 13 mumol/L, range = 11 to 35 mumol/L) and other abnormalities typical of patients with cirrhosis. The patients' mean percentile scores on the digit symbol and block design subtests, from the Wechsler Adult Intelligence Scale (revised), and Purdue pegboard test were 11 +/- 7, 24 +/- 7 and 7 +/- 8 (right hand). Tests of vocabulary, memory, and new learning were normal. The technique of statistical parametric mapping was used to identify regions where cerebral 18F-fluorodeoxyglucose uptake and metabolism were abnormal. We noted significant reductions in the cingulate gyrus, a center mediating attention, target analysis and response formulation and significant increases in visual associative regions subserving motion and color perception and object orientation. We suggest that minimal hepatic encephalopathy is due to a deficit in the detection and formulation of responses to visual stimuli, a function of the cingulate, which is a part of the anterior attentional system of the brain. Increases in 18F-fluorodeoxyglucose metabolism may be compensatory. These studies show that brain regions differ in their sensitivity to the agents that cause hepatic encephalopathy and that positron-emission tomography is useful in studying the pathophysiology of this disorder.

Adult↗
PubMed1995

Vision in dogs.

Compared with the visual system in human beings, the canine visual system could be considered inferior in such aspects as degree of binocular overlap, color perception, accommodative range, and visual acuity. However, in other aspects of vision, such as ability to function in dim light, rapidity with which the retina can respond to another image (flicker fusion), field of view, ability to differentiate shades of gray, and perhaps, ability to detect motion, the canine visual system probably surpasses the human visual system. This has made the dog a more efficient predator in certain environmental situations and permits it to exploit an ecological niche inaccessible to humans.

Animals↗
PubMed1987

A central binocular mechanism affects chromatic adaptation.

Two experiments explored the role of central binocular mechanisms in color perception. The first experiment examined the effect of adapting to simultaneous, binocularly fused fields. Each eye adapted to a slowly flickering (0.5 Hz) long-wavelength light. The two eyes were adapted either inphase (both eyes stimulated at the same moment) or out-of-phase (only one eye stimulated at any given moment). Both adapting procedures shifted equilibrium yellow toward longer wavelengths, but a significantly greater shift was found when adapting light stimulated both eyes simultaneously. This reveals that a central binocular mechanism affects chromatic adaptation. The second experiment tested whether the binocular mechanism could shift equilibrium yellow measurements made with both eyes (identical, binocularly fused fields presented to each eye) outside of the range of measurements established by left-eye monocular viewing and right-eye monocular viewing. Differences were found between monocular left-eye and monocular right-eye color appearance under conditions of moderate chromatic adaptation, but binocularly fused measurements fell within the range established by the monocular results. This is consistent with the view that central mechanisms serve to keep the two eyes in balance, rather than systematically alter color appearance from colors perceived under monocular viewing.

Adaptation, Ocular↗
PubMedDate not supplied

[Spectral filters as a method of therapeutic correction].

Spectral filters were used for additional correction of vision in 67 patients: in 15 adults with initial cataracts (intensive yellow filter), 26 children with albinism (yellow-brown filter), 14 children with macular hypoplasia (orange filter), and 12 children with aphakia after removal of congenital cataracts (yellow filter). Selection of the filter density is carried out using a special method including visocontrastometry, examination of sensitivity to lateral light, and study of color perception thresholds. Use of filters resulted in improvement of the vision acuity by 43.5% in patients with initial cataracts, by 10% in those with albinism, by 20% in those with macular hypoplasia, and by 22% in those with aphakia; moreover, an improvement of the frequency-contrast characteristics was observed, as well as a reduction of photophobia, and a reduction of vision amplitude in patients with nystagmus. The possible applications of spectral correction are discussed.

Adult↗