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At least 19 recordsLinked to original sources
PubMed1999

Chromatic induction with remote chromatic contrast varied in magnitude, spatial frequency, and chromaticity.

Chromatic induction from a surround is attenuated by chromatic contrast within a remote region outside of the surround (Shevell & Wei, 1998, Vision Research, 38, 1561-1566). The present study reports hue-cancellation measurements that show the attenuation depends on the magnitude, spatial frequency and chromaticity of remote chromatic contrast. Spatial-frequency tuning is shown by maximal attenuation of induction with remote contrast elements of the same size as the test. Experiments with various chromaticities of remote contrast show that S-cone stimulation within the remote region has a much weaker effect than L-/M-cone chromatic contrast, and does not depend on whether the S-cone stimulation is uniform or uneven across the region. Overall, the results show that remote L/M contrast affects classical chromatic induction, with its effect depending on the spatial frequency and magnitude of contrast. The influence of remote S-cone stimulation, on the other hand, is relatively weak and depends on only the S-cone spatial average, at least when S-cone stimulation by the test and its immediate surround is minimal (as in all experiments here).

Color Perception↗
PubMed1988

Transformation of C3H/10T1/2 mouse embryo cells to focus formation and anchorage independence by insoluble lead chromate but not soluble calcium chromate: relationship to mutagenesis and internalization of lead chromate particles.

The genotoxicity of soluble and insoluble hexavalent chromium compounds was studied in mammalian cell assays which detect base substitution, deletion, addition, and frameshift mutations [6-thioguanine resistance in Chinese hamster ovary cells], primarily base substitution mutations [ouabain resistance in Chinese hamster ovary and C3H/10T1/2 Cl 8 mouse embryo fibroblasts (10T1/2)] and morphological transformation [focus formation] in 10T1/2 cells. Soluble hexavalent CaCrO4, administered in either acute (5-h) or subacute (24-h) dosing regimens, induced dose-dependent cytotoxicity and mutation to 6-thioguanine resistance in Chinese hamster ovary cells but no mutation to ouabain resistance or focus formation in transformation assays, although the acute treatment induced a high frequency of conversion of 10T1/2 cells to adipocytes. Cell lines established from cloned adipocytic cells were not morphologically transformed and did not grow in soft agarose. PbCrO4 did not induce mutation to either 6-thioguanine or ouabain resistance but did induce a reproducible dose-dependent, low frequency of focus formation in 10T1/2 cells. Cell lines established from PbCrO4-induced foci stably formed foci when coseeded with 10T1/2 cells, had 3-5-fold increased saturation densities relative to nontransformed 10T1/2 cells, and formed colonies in soft agarose, indicating their likelihood to be neoplastic. Long term exposure of 10T1/2 cells to either CaCrO4 or PbCl2, even at 85% cytotoxic concentrations, or pretreatment of cells with either CaCrO4 or PbCl2 followed by treatment with the alternate compound, did not induce morphological transformation. Treatment of cells with insoluble hexavalent PbCrO4 resulted in progressive and extensive vacuolization of cells in contact with the particles. Progressive cytoplasmic engulfment of PbCrO4 particles was observed using scanning electron microscopy, although PbCrO4 particles were not observed inside vacuoles. These results indicate that the soluble clastogens K2Cr2O7 and CaCrO4 were probably mutagenic by a non-base substitution mechanism but could not transform 10T1/2 cells. In contrast, PbCrO4 was not detectably mutagenic but induced transformation, which could not be explained solely by acute or chronic exposure to dissolution products of either lead or chromate alone. Since PbCrO4 particles were found to be intracytoplasmic in extensively vacuolated cells, we suggest that the unique physiochemical properties of PbCrO4 particles, leading to their internalization and the resultant associated cellular stress response, may be related to the transformation induced by this compound.

Adipose Tissue↗
PubMed1992

Plasmid chromate resistance and chromate reduction.

Compounds of hexavalent chromium (chromates and dichromates) are highly toxic. Plasmid genetic determinants for chromate resistance have been described in several bacterial genera, most notably in Pseudomonas. Resistance to chromate is associated with decreased chromate transport by the resistant cells. The genes for a hydrophobic polypeptide, ChrA, were identified in chromate resistance plasmids of Pseudomonas aeruginosa and Alcaligenes eutrophus. ChrA is postulated to be responsible for the outward membrane translocation of chromate anions. Widespread bacterial reduction of hexavalent chromate to the less toxic trivalent chromic ions is also known. Chromate reduction determinants have not, however, been found on bacterial plasmids or transposons. In different bacteria, chromate reduction is either an aerobic or an anaerobic process (but not both) and is carried out either by soluble proteins or by cell membranes. Chromate reduction may also be a mechanism of resistance to chromate, but this has not been unequivocally shown.

Amino Acid Sequence↗
PubMed2000

Infant color vision: sharp chromatic edges are not required for chromatic discrimination in 4-month-olds.

In our previous demonstrations of chromatic discrimination in infants, we have used test and surround fields of different chromaticities that abutted each other at sharp chromatic edges. In order to see whether sharp chromatic edges are necessary for infants to make chromatic discriminations, 16-week-old infants were tested with three stimulus configurations in which sharp chromatic edges were eliminated. The three edge manipulations involved black borders, a dark surround, or blurred edges around the chromatic test field. In each case red, green, and violet test fields were used. Although performance decreased when sharp chromatic edges were eliminated, observers' percent correct scores remained clearly above chance for eight of the nine discriminations (three colors x three edge manipulations). We argue that all three edge manipulations reduce the likelihood of mediation of chromatic discrimination by M (magnocellular) cells. These data thus provide evidence that young infants have functional P (parvocellular) pathways, and use them for making chromatic discriminations.

Color Perception↗
PubMed1977

The significance of chromate ingestion in patients allergic to chromate.

A double-blind study was carried out to demonstrate the significance of chromate ingestion in the persistence of chromic chromate dermatitis. Each of 31 chromate-allergic patients was given one tablet containing 7.1 mg potassium dichromate, plus a placebo tablet. The dermatitis of 11 of the 31 patients flared after the ingestion of chromate, but not after placebo. 3 patients had equivocal reactions to both tablets; the dermatitis worsened in 2 patients following ingestion of the placebo but not after the chromate tablet. No statistically significant difference could be found between reactivity to chromate and eczema of dyshidrotic morphology. Nor was it possible to correlate the degree of patch test reactivity to the reaction following chromate ingestion. It is concluded that a low-chromate diet is of value in the management of patients with chronic chromate dermatitis.

Administration, Oral↗
PubMed1989

[Chromatic study of composite resins. Report 1. The influence of the color measuring instruments and the background colors on the chromatic values].

The purpose of this study was to investigate the influence of the structural difference of the color measuring instruments and the background colors on the chromatical values of the composite resins. Composite resin disks which were 10 mm in diameter and 1 mm and 2 mm in thickness, and made by the light-cured composite resin Silux Plus (3M Co.) were chromatically measured. The colors of the composite resin used in this study were universal, yellow, dark-yellow and light. The color measuring instruments used in this study were the Murakami Color Research Laboratory Fast Spectrophotometer CMS-500 used with the Flexible Sensor FS-1, FS-2 and FS-3, and the Murakami Color Research Laboratory Color Difference Meter CD-270 used with the Improved Light Guide CD-270. The diameters of the head which receives the light from the object were: FS-1 (2 mm), FS-2 (3 mm), FS-3 (5 mm) and Improved Light Guide CD-270 (2 mm). The chromatical values of the resin specimens were measured without back color, backed by a white plate and backed by a black plate. The chromatical values of the composite resin disks were measured with the different color measuring instruments under the different background colors. The XYZ, L*a*b* and xy values were compared and the following results were obtained. 1) The chromatical XYZ, L*a*b* and xy values of the composite resins showed different value patterns among the color measuring instruments. 2) Different influences of the background colors on the chromatical values of the composite resins were obtained among the different colors and different thicknesses of the resins in the cases of some color measuring instruments were used. 3) The most precise color measuring instrument for chromatical measuring of the composite resins among the instruments used in this study was the Fast Spectrophotometer CMS-500 used with the FS-3. 4) Prior to the comparison of the chromatical values measured by the different color measuring instruments, the chromatical values obtained by measurement with the same specimens should be compared and the structural differences, the precision and the sensitivities of the instruments should be understood.

Color↗
PubMed1999

Chromate efflux by means of the ChrA chromate resistance protein from Pseudomonas aeruginosa.

Everted membrane vesicles of Pseudomonas aeruginosa PAO1 harboring plasmid pCRO616, expressing the ChrA chromate resistance protein, accumulated four times more (51)CrO(4)(2-) than vesicles from plasmidless cells, indicating that a chromate efflux system functions in the resistant strain. Chromate uptake showed saturation kinetics with an apparent K(m) of 0.12 mM chromate and a V(max) of 0. 5 nmol of chromate/min per mg of protein. Uptake of chromate by vesicles was dependent on NADH oxidation and was abolished by energy inhibitors and by the chromate analog sulfate. The mechanism of resistance to chromate determined by ChrA appears to be based on the active efflux of chromate driven by the membrane potential.

Bacterial Proteins↗
PubMedDate not supplied

Chromate allergy: total chromium and hexavalent chromate in the air.

This is a study on atmospheric concentration of total chromium and hexavalent chromate and its role in chromate sensitivity. Air concentration of total chromium and hexavalent chromate in a construction factory, a busy city area, a suburban area, a residential area, and a heavy industrial area were measured by air sampling pumps. Hexavalent chromate was not detected in any sampled areas. Two (concreting areas) of 8 locations in the construction factory had total chromium of 0.2 and 2.3 micrograms/m3 in the atmosphere. It appeared that the atmospheric concentration of total chromium and hexavalent chromate was negligible. These findings indicate that unexplained chromate sensitivity, as so often seen in patients attending a contact dermatitis clinic, is not attributable to exposure to hexavalent chromate in the air.

Chromates↗
PubMed1989

The interactions between chromatic aberration, defocus and stimulus chromaticity: implications for visual physiology and colorimetry.

It has long been recognised that chromatic aberration can introduce luminance artifacts into nominally isoluminant colour stimuli. In this study the effects of chromatic aberration (along with those of defocus and stimulus spatial frequency) on the chromaticity of the retinal image are considered. Such optical effects have important methodological and functional implications for visual physiology. The "Silent Substitution" principle is a fundamental feature of modern colorimetry, being employed in both psychophysical and electrophysiological approaches to the visual system. The theoretical colour spaces introduced by MacLeod and Boynton (1979) and Derrington et al. (1984) are also ultimately based on this principle. All such applications of the silent substitution principle are sensitive to the optical effects of chromatic aberration, defocus, spatial frequency and stimulus chromaticity. The spatial acuity of the mechanisms of colour vision are appreciably lower than those of the luminance system (Mullen, 1985). In addition chromatic aberration has been shown to be a cue to ocular accommodation (Fincham, 1951). The analysis presented in this study suggests a possible explanation for these findings in terms of the ecological and computational constraints placed on the visual system by chromatic aberration.

Color Perception↗
PubMed2001

Chromate reduction by a pseudomonad isolated from a site contaminated with chromated copper arsenate.

A pseudomonad (CRB5) isolated from a decommissioned wood preservation site reduced toxic chromate [Cr(VI)] to an insoluble Cr(III) precipitate under aerobic and anaerobic conditions. CRB5 tolerated up to 520 mg of Cr(VI) liter(-1) and reduced chromate in the presence of copper and arsenate. Under anaerobic conditions it also reduced Co(III) and U(VI), partially internalizing each metal. Metal precipitates were also found on the surface of the outer membrane and (sometimes) on a capsule. The results showed that chromate reduction by CRB5 was mediated by a soluble enzyme that was largely contained in the cytoplasm but also found outside of the cells. The crude reductase activity in the soluble fraction showed a K(m) of 23 mg liter(-1) (437 microM) and a V(max) of 0.98 mg of Cr h(-1) mg of protein(-1) (317 nmol min(-1) mg of protein(-1)). Minor membrane-associated Cr(VI) reduction under anaerobiosis may account for anaerobic reduction of chromate under nongrowth conditions with an organic electron donor present. Chromate reduction under both aerobic and anaerobic conditions may be a detoxification strategy for the bacterium which could be exploited to bioremediate chromate-contaminated or other toxic heavy metal-contaminated environments.

Aerobiosis↗
PubMed1984

Lung cancer mortality among workers making lead chromate and zinc chromate pigments at three English factories.

Lung cancer mortality among 1152 men working at three English chromate pigment factories was studied from the 1930s or 1940s until 1981. Workers at factory C were exposed only to lead chromate and experienced normal mortality (Obs/Exp deaths 7/6.45). Workers at factories A and B were exposed to both lead and zinc chromate; mortality was normal among those who had only low exposure (O/E 7/6.95). For workers with high or medium exposure lung cancer mortality was significantly raised among men remaining at least a year after entering service at factory A during 1932-54 (O/E 21/9.45) and at factory B during 1948-67 (O/E 11/2.50). At factory A, 1933-46 entrants staying only 3-11 months were not affected (O/E 6/5.04) and 1955-63 entrants also appeared unaffected (O/E 2/2.00); working conditions there improved in 1955. The hazard at factories A and B affected workers who left after one year as well as those with longer service, and latent intervals were unusually short. The results indicate that moderate or heavy exposure to zinc chromate may give rise to a severe risk of developing lung cancer, but that exposure which is relatively mild or lasts less than a year may not constitute an effective risk. The results provide no indication that lead chromate induces lung cancer in man, even under conditions conducive to lead poisoning.

Adult↗
PubMed1989

Dependence of the chromatic valence function on chromatic standards.

The red, green, yellow, and blue curve portions of chromatic valence functions (CVFs) were measured by an iso-cancellation technique using three or four different chromatic standards (cancellation stimuli of fixed intensity and chromaticity) for each of the four curve portions. Curve shapes of the red, green, and yellow CVF portions varied with different chromatic standards, while that of blue did not. These results of chromatic standard dependency in CVFs are discussed with respect to opponent equilibria in a color mixture space.

Adult↗
PubMed1993

Chromatic discrimination with variation in chromaticity and luminance: data and theory.

Boynton and Kambe developed a model of chromatic discrimination in which thresholds are mediated by two independent mechanisms: the short-wavelength sensitive (S-) cones (S-cone axis), and the middle-wavelength sensitive (M-) and long-wavelength sensitive (L-) cones (M/L-cone axis). In this study, we used a Maxwellian view optical system to investigate fundamental properties of the model as a function of chromaticity and luminance. We confirmed that discriminations along the S-cone axis were dependent on S-cone excitation level. However, changes in chromaticity and changes in mean luminance were not described by a single threshold-vs-radiance (TVR) template. We developed a model to account for the different effects of changing S-cone excitation by varying mean chromaticity and by varying mean luminance. M/L-cone discriminations showed a minimum at the L-cone excitation to white, indicating strong opponency. The thresholds increased with luminance approaching a Weber region and showing parallel functions for differing chromaticities. These data are fit by a model allowing retinal gain controls and spectral opponency.

Adult↗
PubMed1989

The gap effect revisited: slow changes in chromatic sensitivity as affected by luminance and chromatic borders.

Chromatic discrimination was studied with two half-fields that were either precisely juxtaposed or were separated by a narrow gap. When present, the gap was in some conditions filled with light isoluminant to the test fields. When the fields were juxtaposed, chromatic sensitivity declined with viewing duration. For a discrimination based solely on S cone activity, separating steadily-viewed fields by either a luminance or a purely chromatic gap caused similar enhancements of sensitivity. Neither type of gap had much effect when the fields were flashed. The results may be interpreted as showing that either a luminance or chromatic contour can spatially delimit the two half-fields, thus preventing a slow spatial integration from reducing the discriminability of the two sides of the field.

Adult↗
PubMed1990

Chromate-resistance in a chromate-reducing strain of Enterobacter cloacae.

Resistance to toxic hexavalent chromium (chromate: CrO4(2)) in Enterobacter cloacae strain HO1, isolated from an activated sludge sample, was investigated under aerobic and anaerobic conditions. Decreased uptake of 51CrO4(2-) in E. cloacae strain HO1 was observed under aerobic conditions, when compared with a standard laboratory E. cloacae strain (IAM 1624). Under anaerobic conditions E. cloacae strain HO1 was able to reduce hexavalent chromium to the less toxic trivalent form. When E. clocacae strain HO1 was grown with nitrate anaerobically, the cells were observed to lose simultaneously their chromate-reducing ability and chromate-resistance under anaerobic conditions.

Anaerobiosis↗
PubMed1983

[Penetration of chromate ions in damaged and undamaged skin of sensitized and nonsensitized individuals occupationally exposed to chromates].

The importance of oversensitivity to chromate within the framework of occupational dermatoses is sufficiently well known. Questions still remained unanswered as to which substances and solutions in which form and quantity sensitivity to chromate occurs. Further, it is unclear why one worker reacts allergically and another remains unaffected carrying out the same work. In spite of all attempts it is as a rule still impossible to predict who will be affected. By investigating the penetration of chromate ions, we wanted to draw attention to possible dangers those beginning work are exposed to. We are aware that a complex series of questions exists but that only a small part can be approached at once. It appeared appropriate to determine whether the level of penetration of the metal ions differs between individuals, in particular whether the rate is higher in sensitive than in non-sensitive people. To handle this question a method had to be found to determine metal ions with and without exposure in the skin.

Chromates↗
PubMed2002

Accommodation to simulations of defocus and chromatic aberration in the presence of chromatic misalignment.

Previous studies have demonstrated that accommodation will respond to sine gratings in which the relative modulations of red, green and blue image components have been altered to simulate the effects of defocus and longitudinal chromatic aberration. The present study aimed to determine the tolerance of the accommodative system to relative phase shifts in those components induced by chromatic misalignment. It was found that accommodation can tolerate moderate amounts of chromatic misalignment (6'), but responds adversely when misalignments are large. Applications to visual display terminals and spectacle lens and instrument design are discussed.

Accommodation, Ocular↗
PubMed2002

The influence of chromatic and achromatic variability on chromatic induction and perceived colour.

Judgments of the colour of a surface are influenced by the colour of the surrounding. To determine whether only the average colour of the surrounding matters, or also the chromatic variability, judgments in colourful scenes are often compared with ones in which a target is surrounded by a plain background that provides the same average physical illumination of the retina as the colourful scene. The variability sometimes makes a difference (eg Shevell and Wei, 1998 Vision Research 38 1561-1566), and sometimes it does not (eg Brenner and Cornelissen, 1998 Vision Research 38 1789-1793). Is this because of the nonlinearity in cone responses? We designed scenes that stimulated the cones in an equivalent manner, both on average and in terms of variability, and yet differed markedly in chromatic variability. The more colourful surroundings had considerably less influence on subjects' colour judgments. We conclude that early cone-specific regulation of sensitivity cannot be responsible for the change in perceived colour, and deduce that chromatic induction takes place after contrast gain control.

Color Perception↗