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PubMed1979

Luminace, not brightness, determines temporal brightness enhancement with chromatic stimuli.

Brightness-duration relations for chromatic stimuli were studied using three pulse-to-background luminace relations: chromatic equal-luminance pulses (3.2 cd/m2) were presented as increments of 0.3 or 1.0 log units above a lower luminance achromatic background, or were presented in hue substitution, equated in luminance to the achromatic background, so that no spatio-temporal luminance transients occurred during stimulus presentation. Incremental pulses produced temporal brightness enhancement (the Broca-Sulzer phenomenon), but hue substitution pulses did not. Temporal brightness enhancement thus depends upon the occurrence of luminance transients and cannot be produced by pulsed-to-background brightness differences associated solely with chromaticity differences.

Color Perception↗
PubMed1979

Sister chromatid exchanges induced in cultured mammalian cells by chromate.

Chromate compounds induced sister chromatoid exchanges (SCEs) and chromosome aberrations in cultured mammalian cells. Similar increases in SCE frequency were observed in human fibroblasts exposed to the compounds K2Cr2O7 and K2CrO4. Marked increases in SCE frequency in cells exposed to chromate for a 48-h period were detected at concentrations between 10(-7) and 10(-6) M. Chromosome aberrations (primarily chromatid breaks) were also produced in human cells exposed to K2CrO4 at concentrations between 8 . 10(-7) and 3 . 10(-6) M. K2CrO4, but not the trivalent compound CrCl3, induced SCEs in Chinese hamster ovary (CHO) cells at low concentrations.

Adult↗
PubMed1977

Relapse of chromate dermatitis from sheet metal.

Galvanised sheet metal has previously been described as a source of chromate dermatitis (Fregert et al. 1970). We report a patient who appears to have been sensitised many years previously by an entirely different source of chromate, but whose resulting hand eczema has relapsed while handling galvanised sheet metal at work.

Adult↗
PubMed1977

Chromate dermatitis from a boiler lining.

Chromate dermatitis is described in a mechanical fitter working inside boiler combustion chambers. A source of hexavalent chromate is traced to the action of the heat and alkaline fuel ash on trivalent chrome ore in parts of the refractory lining. Removal of the patient from this contact has resulted in almost complete clearing of his dermatitis, without any relapse, during a 9-month follow-up period.

Chromates↗
PubMed1978

Lung cancer in Japanese chromate workers.

We have treated ten patients with lung cancer among workers in a chromate factory between 1972 and 1976. Four further cases were also found through death certificates and medical records. Most were smokers and all were men. The average duration of exposure to chromate was 24 years (range 10 to 36). The cell type in our ten patients was squamous in seven and small anaplastic type in three. The primary sites were all in large bronchi. The incidence (person per year) calculated from the number of employees, duration of factory activity, number of cancer patients, and shortest duration of labour period among the patients was 657.9 per 100,000 compared to 13.3 per 100,000 in Japan as a whole.

Adult↗
PubMed1979

[The persistence of chromate allergy in cement eczema].

93 patients with contact allergy to chromates were followed up for 15 years during which time they were examined clinically and patch tested quantitatively at regular intervals. Results demonstrate that contact allergy to chromates and cement eczema differ from other occupational dermatoses mainly because of their persistence after a change of exposure and occupation. Explanations for this observation are offered.

Adult↗
PubMed1978

The use of chromium-51 sodium chromate for the detection of food and chemical sensitivities.

Both antibody mediated lysis of human RBC's and toxic hemolysis were found to occur with chemicals used as coloring agents for foods, drugs and cosmetics. Because of the strong chromaticity of these dyes, chromium-51 sodium chromate was bound to the hemoglobin of target human RBC's and its efflux was used as an indicator of lysis instead of spectrophotometry, which had been used with food antigens. The major antibody effect was noted when treatment of the target RBC's with antiIgG resulted in a marked inhibition of lysis, indicating that IgG is a lysis-promoting factor (LPF) in this system. Weaker effects were noted by treatment of the target RBC's with monospecific antisera for the other four classes of immunoglobulin and for alpha2-macroglobulin. No neutralizing effects were observed by pre-incubation of the dyes with autologous serum prior to the addition of RBC's.

Chromates↗
PubMed1978

[Spectral sensitivity of off-response in human VECP during selective chromatic adaptation (author's transl)].

The spectral sensitivity of the visual system of man during selective chromatic adaptation was determined. The criterion was an off-response of constant amplitude in the evoked cortical potential. Criterion of height of response differed among the subjects investigated. Generally, a pupillary radiant intensity between 0.4 and 1.0 lg unit above the sensory threshold was used. With stimulation of both the green- and the red-sensitive mechanism, the sensitivity of the off-response was low. It was high if either the green or the red mechanism were suppressed by selective chromatic adaptation. Demonstration of an opponent color mechanism in the visual system was easier with recording of the off-response in the VECP than with determination of the sensory threshold. The presence of the blue-sensitive mechanism as revealed by the VECP off-response was shown for light stimuli near the sensory threshold during adaptation which orange and red light for a late response of low amplitude.

Adaptation, Physiological↗
PubMed1975

Spatial and chromatic properties of neurons subserving foveal and parafoveal vision in rhesus monkey.

The response properties of neurons in the region of striate cortex subserving central retina (0 degrees-2 degrees) and in a region of representation of parafoveal retina (4 degrees-7 degrees) were studied in unanesthetized paralyzed macaque monkeys. Neurons sensitive to the orientation of the stimulus in the visual field (simple, complex, and hypercomplex), and neurons lacking orientation selectivity (concentric, and a new class termed uniform) were found. In foveal cortex non-oriented cells were more numerous, and orientation sensitive cells had less strict spatial stimulus requirements than in parafoveal cortex. Most neurons received a monocular input, either exclusively or very predominantly. Three types of neurons were recognized on the basis of their responses to chromatic stimuli. (1) Luminosity neurons (about half the population) gave the same qualitative response to all effective wayelengths and had a spectral sensitivity similar to that of the macaque, determined behaviorally. Cells with all spatial types of receptive fields, except simple, occurred in this group. (2) Spectrally-treated neurons also responded in the same manner to different wavelengths, but over a narrower range than luminosity neurons, and their maximal sensitivity was shifted toward one or the other end of the visible spectrum. All tuned neurons had uniform or complex receptive field. (3) Spectrally-opponent neurons were either excited or inhibited by long wavelengths and responded in the opposite manner to short wavelengths. For cells with uniform or complex receptive fields the two opponent systems were coextensive. Simple or concentric neurons often had dual-opponent organization. The distribution of functional types among different cortical layers was similar in parafoveal and foveal cortex. The functional attributes of ocular dominance and orientation sensitivity were found to be statistically independent dimensions of cortical organization. On the other hand, the correlation between spatial and chromatic properties did not vary between different cytoarchitectonic layers, a finding suggesting that these neuronal properties depend on conjoined projectional and intracortical connecting mechanisms.

Animals↗
PubMed1979

Opponent chromatic mechanisms: relation to photopigments and hue naming.

Opponent chromatic response functions were determined from monochromatic, equal-luminance stimuli from 400 to 700 nm for three observers using a hue cancellation procedure. The same observers scaled the hue of the stimuli using the terms red, green, yellow, and blue. The results showed that the hue scaling was accurately predicted from the cancellation functions using the model of Hurvich and Jameson. Theoretical curves were generated to fit the chromatic response functions with a linear combination of three cone photopigments. The theoretical photopigments were based on an idopsin nomogram with lambdamax at a = 435, beta = 530, and lambda = 562 nm. An estimate of the density of each observer's preretinal optic media was obtained in order to relate the photopigment absorption spectra to the psychophysical data. Good linear fits were obtained for each observer's red-green curve, but not for the yellow-blue curves. A nonlinear model with an expansive exponent was used to fit the yellow-blue response functions with the three theoretical photopigments.

Adult↗
PubMed1979

Using color substitution pupil response to expose chromatic mechanisms.

It is well known that pupillary threshold shows a scotopic spectral behavior, even for foveal stimuli. However, when two scotopically balanced fields at different wavelengths are alternated, the pupil shows a constriction response at each transition, exposing innervation from chromatic mechanisms. Using a suitable model for pupillary innervation, this substitution response is systematically studied for different wavelengths and radiant power levels to yield (within the accuracy of the assumptions of the model) spectral threshold curves for the chromatic mechanism as indicated by the pupil. Four mechanisms have thus been identified, having peak sensitivities near 450, 525, 580, and 495 nm. We propose that these represent the blue, green, red and scotopic mechanisms as maintained before the level of the lateral geniculate body.

Color Perception↗
PubMed1979

A postal survey of patients with nickel and chromate dermatitis.

A postal survey was made of 75 patients with nickel and chromate dermatitis who had been discharged from the clinic; 69% of patients replied to the questionnaire and in 81% of these the dermatitis was still active. In many patients (48%) this was causing significant disability long after initial presentation to the clinic (average of 56.5 months). All patients had patch tests performed and the relevance of this is discussed with reference to nickel dermatitis.

Allergens↗
PubMed1977

Chemical stabilization of Golgi silver chromate impregnations.

Blocks of neural tissue were processed by a modified Golgi-Kopsch procedure and by the rapid Golgi method. Following the impregnation, the blocks were embedded in celloidin, sectioned at 100 micrometer, and collected in 70% alcohol. The sections were then processed as follows: 1) rinsed in distilled water; 2) substituted with 0.4M sodium bromide for five minutes; 3) reduced in Kodak D-19 developer; and 4) treated in 0.5M sodium thiosulfate. The silver chromate deposits within the impregnated cells are converted successively to silver bromide and to reduced silver by this procedure. Sections so treated resist decomposition of the Golgi impregnation, and they may be counterstained with conventional aqueous cresyl violet to demonstrate the cytoarchitecture of the Golgi-impregnated tissue.

Animals↗
PubMed1979

A quantitative study of chromatic organisation and receptive fields of cells in the lateral geniculate body of the rhesus monkey.

The responses of neurones in the lateral geniculate nucleus (LGN) were investigated in anaesthetised rhesus monkeys. A new classification for cells in the parvocellular layers (PCL) is proposed, based on their spectral response curve and their response to white stimuli: (A) narrow-band, short wavelength (NS) excited cells, activity suppressed by white stimuli; (B) wide-band, short-wavelength (WS) excited cells, excited by white stimuli; (C) wide-band, long-wavelength (WL) excited cells, (D) narrow-band, long-wavelength (NL) excited cells, activity suppressed by white stimuli; (E) light suppressed (LI) cells, activity suppressed by all wavelengths, usually with some concealed excitatory input at extreme short or long wavelengths. Responses to moving bars and to spots of various diameters (area response curves) were determined for various wavelengths. It was found that the receptive fields from which wavelength-dependent excitatory or suppressive effects could be elicited are concentrically superimposed. The spectral responsiveness of the excitatory inputs to individual cell types corresponds to the absorption curves of single cones (S-, M- or L-cone for NS, WS and WL cells respectively), the spectral distribution of the suppressive mechanisms of all cells was panchromatic and approximately fitted to a sum of all cones. The excitatory input to NL-cells cannot be related to any of the known cone absorption curves, and a simple (L-M) subtraction model is questioned. Neurones in the magnocellular layers (MCL) can be divided into on- and off-centre cells as in the cat's LGN and give qualitatively similar responses over the whole spectrum. In contrast to the tonic responses of PCL cells, MCL cells respond phasically to chromatic and white flashed spots, even with the smallest stimuli. Implications of these findings for colour processing in the LGN are discussed.

Animals↗
PubMed1977

[Chromatic adaptation produces opposite effects on the on and off responses of the photopic electroretinogram (author's transl)].

The electrical response of the light adapted human eye to onset (a-wave) and offset (d1-wave of the positive off-effect) of monochromatic test stimuli between 448 and 654 nm (Ganzfeld stimulation, duration of test flash 0.3 s) was recorded by means of the electroretinogram in 10 normal observers during steady illumination of various wavelengths of 2.2 log Troland. During exposure to white light the spectral sensitivity of the a-wave and off-effect as determined by a criterion amplitude of 25 micronV were similar, the sensitivity of the off-effect being 0.4 log units lower as compared to the a-wave. Blue adaptation (467 nm) decreased the sensitivity of the a-wave and increased the sensitivity of the off-effect within the short wavelengths region of the spectrum. Red adaptation (630 nm) decreased the sensitivity of the a-wave and increased the sensitivity of the off-effect within longer wavelengths. Green adaptation (530 nm) produced only a small decrease of sensitivity of the a-wave for green test light, the sensitivity of the off-effect remained constant. The opposite changes of the a-wave and off-effect during chromatic adaptation demonstrate different participation of these components in the generation of color mechanisms in the human retina.

Adaptation, Ocular↗
PubMed1979

Retinoscopy and chromatic aberration.

The origin of the apparent farsightedness as revealed by retinoscopy in smaller eyes was investigated by using monochromatic retinoscopy on wild rabbits. Our results indicate that a combination of long wavelength light and chromatic aberration of the subject's dioptrics is the major source of this artifact.

Animals↗
PubMed1979

Receptoral and postreceptoral visual processes in recovery from chromatic adaptation.

The time course of recovery from chromatic adaptation in human vision was tracked by determining the wavelength of light that appears uniquely yellow (neither red nor green) both before and after exposure to yellowish green and yellowish red adapting lights. Recovery is complete within 5 min after steady light exposure. After exposure to the alternating repeated sequence 10-sec light/10-sec dark, the initial magnitude of the aftereffect is reduced but recovery is retarded. The results are interpreted in terms of two processes located at different levels in the hierarchical organization of the visual system. One is a change in the balance of cone receptor sensitivities; the second is a shift in the equilibrium baseline between opposite-signed responses of the red/green channel at the opponent-process neural level. The baseline-shift mechanism is effective in the condition in which repeated input signals originating at the receptors are of sufficient strength to activate the system effectively. Hence, this process is revealed in the alternating adaptation condition when the receptors undergo partial recovery after each light exposure, but receptor adaptation during continued steady light exposure effectively protects the subsequent neural systems from continued strong activation.

Color↗