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PubMed2006

Responding to color: the regulation of complementary chromatic adaptation.

The acclimation of photosynthetic organisms to changes in light color is ubiquitous and may be best illustrated by the colorful process of complementary chromatic adaptation (CCA). During CCA, cyanobacterial cells change from brick red to bright blue green, depending on their light color environment. The apparent simplicity of this spectacular, photoreversible event belies the complexity of the cellular response to changes in light color. Recent results have shown that the regulation of CCA is also complex and involves at least three pathways. One is controlled by a phytochrome-class photoreceptor that is responsive to green and red light and a complex two-component signal transduction pathway, whereas another is based on sensing redox state. Studies of CCA are uncovering the strategies used by photosynthetic organisms during light acclimation and the means by which they regulate these responses.

Adaptation, Physiological↗
PubMed1990

A chromatic horizontal cell in the Xenopus retina: intracellular staining and synaptic pharmacology.

1. We identified a chromatic-type horizontal cell (C-cell) in the Xenopus retina by intracellular dye injection with Lucifer yellow or horseradish peroxidase (HRP). C-cells hyperpolarized in response to blue light and depolarized in response to red light. 2. In either photopic or mesopic states, moderate-intensity blue and red stimuli evoked responses that were inverted with respect to each other but of similar waveform and latency. In the presence of a bright green adapting field, the maximal voltage (Vmax) of the hyperpolarizing and depolarizing response component approached 30 mV; the kinetics of both waveforms were fast, and the hyperpolarizing response was followed by a small depolarizing overshoot at light OFF. Thus the blue-sensitive photoreceptor is capable of initiating large visual signals under photopic conditions when transmission from green-sensitive rods is suppressed. Under mesopic conditions (no adapting field) the kinetics of both waveforms were slower. The Vmax of the hyperpolarizing response reached 30-40 mV, whereas the cone-mediated depolarization saturated at 15 mV. 3. Both response components of the C-cell showed large receptive fields with no center-surround antagonism. 4. The C-cell perikaryon was located in the distal inner nuclear layer. It emitted four to seven long, tapering processes that ran horizontally for 90-100 microns. Two kinds of terminal dendrites, short and long, extended from the tapering processes toward the layer of photoreceptor bases. 5. Glycine (5-10 mM) completely eliminated the depolarizing response of the C-cell, whereas the hyperpolarizing component was unaffected. In contrast, gamma-aminobutyric acid (GABA; 5-10 mM) had no obvious effect on either component. 6. The C-cell light response was modified in two stages by cis-2,3-piperidine dicarboxylic acid (cis-PDA; 0.5-5 mM): first the depolarizing response disappeared; then the membrane potential hyperpolarized concomitant with a large reduction or elimination of the hyperpolarizing light response. In contrast, DL-2-amino-4-phosphonobutyric acid (APB) had no obvious effect on either response component or the membrane potential of the cell. 7. Our pharmacological findings are consistent with the view that the hyperpolarizing response in the C-cell is mediated by direct synaptic input from a blue-sensitive photoreceptor. The depolarizing response mediated by the red-sensitive cone could be explained by a direct synapse from the red cone or an indirect pathway involving luminosity (L-type) horizontal cells.

Adaptation, Ocular↗
PubMed1994

Broad-tuned chromatic inputs to color-selective neurons in the monkey visual cortex.

1. Input mechanisms of 21 color-selective cells in cytochrome oxidase-rich blobs in layer II/III of the anesthetized and paralyzed monkey primary visual cortex were studied by an iontophoretic administration of the GABAergic receptor antagonist bicuculline methiodide (BMI). 2. Color-selective blob cells become responsive to originally nonresponsive colors of stimuli or brightness contrast stimuli during removal of intracortical inhibition. 3. The magnitudes of the cells' responses to color stimuli during BMI administration were larger than the expected value of response calculated from the previously reported color tuning of color-selective geniculate cells and emission spectra of color stimulus. 4. These results suggest that color-selective blob cells receive a convergence of different types of chromatic inputs and that intracortical inhibition confers selectivity for a given color on them.

Animals↗
PubMed1988

Successful contact sensitization to chromate in mice.

Mice of the randomly bred strain ICR and of the inbred strain BALB/c could be successfully sensitized to chromate by repeated topical applications of a solution of potassium bichromate in dimethyl sulfoxide. The specificity of chromium sensitization was ascertained by ear tests, specific desensitization by intravenous injection of potassium bichromate and by histological ear sections showing marked infiltrates of leukocytes following ear application of chromium-dimethyl sulfoxide in already sensitized animals. It is concluded that mice may provide a useful experimental model for study of contact sensitivity to chromium.

Animals↗
PubMed2002

Influence of chromaticity on vernier and stereo acuity.

Vernier offset thresholds for targets modulated in luminance or isoluminantly along the L-M axis were confirmed to be equal for targets whose contrasts were equal multiples of those required for detection. On the other hand, stereoscopic depth thresholds were elevated by a factor of 10 or more for isoluminantly modulated targets. Thresholds for vernier targets are 2 or 3 times larger with a gap of 20 arcmin than for a gap of 1 arcmin for both isoluminant and luminance targets. On the other hand, stereo thresholds decrease by a factor of 2 to 3 for both classes of target over the same range. We consider our results in the light of recent electrophysiological and psychophysical evidence and conclude that our results are consistent with the notion that stereo thresholds are mediated by a single class of mechanism for targets modulated in luminance or isoluminantly. We test and reject the hypothesis that stereopsis is subserved by independent chromatic and luminance mechanisms.

Color Perception↗
PubMed2005

Chromatic perceptive field sizes change with retinal illuminance.

The effect of retinal illuminance (0.3-3.3 log td) on chromatic perceptive field size was investigated at 10 degrees eccentricity along the horizontal meridian of the temporal retina. Using the 4+1 color-naming procedure, observers described the hue and saturation of a series of monochromatic stimuli (440-660 nm, in 10-nm steps) of various test sizes (.098-5 degrees) after 30-min dark adaptation. Perceptive field sizes of the four elemental hues and the saturation component were estimated for each wavelength at each retinal illuminance. Results indicate that perceptive field sizes for blue, green, yellow, and saturation all decrease with increasing retinal illuminance; the perceptive field size for red is the smallest and invariant with intensity. The influence of rods on perceptive field size may account for some of the results; other factors are also considered.

Adult↗
PubMed2004

Simultaneous comparison of relative damage to chromatic pathways in ocular hypertension and glaucoma: correlation with clinical measures.

PURPOSE: To use a new methodological approach, based on luminance noise, to assess without bias the relative damage of blue-yellow and red-green pathways in ocular hypertension and glaucoma and to correlate obtained measurements with clinical markers of disease progression. METHODS: A psychophysical procedure modified from Cambridge color test was used to assess color discrimination in three different groups: patients with primary open-angle glaucoma (n = 51 eyes), patients with ocular hypertension (n = 95 eyes), and control subjects (n = 46 eyes). Viewing conditions were such that the function of the macula was being tested, using a discrimination task under noisy conditions. Confusion vectors, and parameters obtained from discrimination ellipses were correlated with perimetric and clinical data taken from the same groups. RESULTS: The lengths of the major axis of chromatic discrimination ellipses and all confusion vectors were significantly different between the groups. These measures followed a significant gradient of worsening performance from the control to hypertensive and glaucoma groups, which was steeper for the tritan axis. There was a significant global positive correlation between test parameters and cup-to-disc ratio and a significant negative correlation with the perimetric mean deviation index. Ellipse length in patients with ocular hypertension correlated significantly with the duration of their hypertensive state. CONCLUSIONS: This psychophysical test can detect visual dysfunction in a significant subset of patients with long-term hypertension with preserved visual fields. Macular function is damaged earlier than previously believed, in both the blue-yellow and red-green pathways.

Color Vision Defects↗
PubMed1989

Neural, optical, and search performance in prolonged viewing of chromatic displays.

The effect of prolonged cathode ray tube (CRT) work on the afferent visual neural and focusing system of the human eye was examined by visually evoked potentials (VEPs) and laser optometer techniques, respectively. These measures were compared with parallel measurements of search performance. Ten volunteers performed three 4-hr sessions of a search/decision task on a high-resolution-red/green/blue (RGB) monitor. Stimuli were numbers and symbols presented in a blue/black, red/black, or red/green foreground/background combination. Results showed minimal changes in the neural and focusing responses to each foreground/background combination over time on task. Weak correlations were found between neural-optical and search performance measurements. These data suggest that the use of chromatic stimuli in the color combinations examined do not have a detrimental effect on visual performance.

Adult↗
PubMed2003

Rearing in different photic and spectral environments changes the optomotor response to chromatic stimuli in the cichlid fish Aequidens pulcher.

Developmental plasticity of spectral processing in vertebrates was investigated in fish by using an innate behavior, the optomotor response. Rearing blue acara (Aequidens pulcher; Cichlidae) under white lights of different intensities as well as deprivation of long wavelengths induced significant changes in the animals' responses to chromatic stimuli. Deprivation of short wavelengths had no effect. With this and previous studies on animals reared under similar conditions, we have demonstrated that developmental plasticity in spectral processing is present at a wide range of neural levels, spanning from photoreceptors to behavior. We hypothesize that earlier studies did not reveal such effects because of the rearing and testing conditions used.

Animals↗
PubMed2004

Colour vision in the glow-worm Lampyris noctiluca (L.) (Coleoptera: Lampyridae): evidence for a green-blue chromatic mechanism.

Male glow-worms Lampyris noctiluca find their bioluminescent mates at night by phototaxis. There is good evidence that location of mates by lampyrid beetles is achieved by a single spectral class of photoreceptor, whose spectral sensitivity is tuned to the bioluminescent spectrum emitted by conspecifics, and is achromatic. We ask whether glow-worm phototaxis involves interactions between two spectral classes of photoreceptor. Binary choice experiments were conducted in which males were presented with artificial light stimuli that differ in spectral composition. The normal preference for a green stimulus (lambdamax=555 nm), corresponding to the bioluminescence wavelength produced by signalling females, was significantly reduced by adding a blue (lambdamax=485 nm) component to the signal. This implies an antagonistic interaction between long- and short-wavelength sensitive photoreceptors, suggesting colour vision based on chromatic opponency. Cryosections showed a band of yellow filter pigment in the fronto-dorsal region of the male compound eye, which could severely constrain colour vision in the dim conditions in which the insects signal. This apparent paradox is discussed in the context of the distribution of the pigment within the eye and the photic niche of the species.

Animals↗
PubMed2000

Chromaticity as a signal of ripeness in fruits taken by primates.

We have measured the reflectance spectra of many samples of fruit eaten by chimpanzees and three frugivorous monkey species. If the fruit are plotted in a colour space appropriate for catarrhine primates, several distinct ripening patterns are evident. The degree of ripeness of many species would be discernible by dichromatic primates, but for most fruit a trichromatic consumer would be at an advantage. However, by calculating which set of possible photopigments would maximise the chromatic distance between samples of each fruit species, we show that the spectral positions of the primate long- (L) and middle-wavelength (M) cone pigments are not optimised for this task.

Animals↗
PubMed2006

Chromium on the hands of children after playing in playgrounds built from chromated copper arsenate (CCA)-treated wood.

Children's exposure to arsenic and chromium from playground equipment constructed with chromated copper arsenate (CCA)-treated wood is a potential concern because of children's hand-to-mouth activity. However, there exists no direct measure of Cr levels on the hands of children after playing in such playgrounds. In this study we measured both soluble and total Cr on the hands of 139 children playing in playgrounds, eight of which were constructed with CCA-treated wood and eight of which were not. Children's age and duration of play were recorded. The hands of each child were washed after play with 150 mL deionized water, which was collected in a bag and subsequently underwent analysis of Cr and 20 other elements, using inductively coupled plasma mass spectrometry. Total average Cr on the hands of 63 children who played in CCA playgrounds was 1,112 +/- 1,089 ng (median, 688; range 78-5,875). Total average Cr on the hands of 64 children who played in non-CCA playgrounds was 652 +/- 586 ng (median, 492; range 61-3,377). The difference between the two groups is statistically significant (p < 0.01). Cr levels were highly correlated to both Cu (r = 0.672) and As (r = 0.736) levels in CCA playgrounds (p < or = 0.01), but not non-CCA playgrounds (r = 0.252 and 0.486 for Cu and As, respectively). Principal-component analysis indicates that Cr, Cu, and As are more closely grouped together in CCA than in non-CCA playgrounds. These results suggest that the elevated levels of Cr and As on children's hands are due to direct contact with CCA wood.

Arsenates↗
PubMed2003

Chromatic dispersion and losses of microstructured optical fibers.

Using a rigorous and vector multipole method, we compute both losses and dispersion properties of microstructured optical fibers with finite cross sections. We restrict our study to triangular lattices of air-hole inclusions in a silica matrix, taking into account material dispersion. The fiber core is modeled by a missing inclusion. The influence of pitch, hole diameter, and number of hole rings on chromatic dispersion is described, and physical insights are given to explain the behavior observed. It is shown that flattened dispersion curves obtained for certain microstructured fiber configurations are unsuitable for applications because of the fibers' high losses and that they cannot be improved by a simple increase of the number of air-hole rings.

Journal Article↗
PubMed2004

Improvement of chromatic aberration of a plastic rod lens array. 1. Combination-color lens arrays consisting of several kinds of rod lenses with different gradient constants and different color filter functions.

We propose a new type of rod lens array with improved chromatic aberration. The new rod lens array consists of several kinds of rod lenses with different gradient constants and different color filter functions. The gradient constant of each lens was prepared such that the total conjugate length was identical to the specific wavelength of the lens with a constant lens length. We call our new type of rod lens array a combination-color lens array. The characteristics of this color-type lens array are as follows: high angular aperture, short focal length, and ease of production with established procedures. The optical resolution of the rod lens array is 300 dpi in a wide wavelength range that is high enough to be applied to color scanners.

Journal Article↗
PubMed2005

Chromatic compensation in the near-field region: shape and size tunability.

We report a diffractive-lens triplet with which to achieve wavelength compensation in the near field diffracted by any aperture. On the one hand, the all-diffractive triplet allows us to tune, in a sequential way, the Fresnel-irradiance shape to be achromatized by changing the focal length of one diffractive lens. On the other hand, we can adjust the scale of the chromatically compensated Fresnel diffraction field by shifting the aperture along the optical axis. Within this framework, we present an extremely flexible white-light Fresnel-plane array illuminator based on the kinoform sampling filter. A variable compression ratio and continuous selection of the output pitch are the most appealing features of this novel application.

Journal Article↗
PubMed2006

Chromatic dispersion effects in analog polarization-modulated links.

The effect of chromatic dispersion on a photonic link employing polarization modulation is studied analytically and experimentally. For analog polarization modulation, dispersion introduces a frequency-dependent rotation to the orientation of modulation about the center of modulation. As a result, the dispersion-limited bandwidth of the link will depend on receiver design.

Journal Article↗
PubMed2006

Characterization of chromatic dispersion of optical filters by high-stability real-time spectral interferometry.

Chromatic dispersion of optical filters is characterized by what is believed to be novel broadband spectral interferometry, which is based on dual-wavelength heterodyne measurement of spectral phase. High phase stability is achieved by differential phase detection using two lasers for wavelength-swept probe and phase-tracking reference. The technique provides self-tracking interferometry by passive stabilization of optical phase and allows real-time measurement of spectral phase and group delay with a low phase drift of less than 0.04pi. A fiber Bragg grating and a thin-film filter are characterized by this method.

Journal Article↗
PubMed1977

Chromatic two-pulse resolution with and without luminance transients.

Two-pulse discrimination thresholds determined for homochromatic pulses presented as luminance increments or decrements are invariant with wavelength. Wavelength does affect two-pulse temporal resolution if chromatic pulses are presented in hue substitution, matched in luminance (with flicker photometry) to an achromatic background field. For relatively long pulses, the wavelength effect resembles trichromatic saturation discrimination, with poorest temporal resolution at 570 nm. For shorter pulses, temporal resolution for hue substitution stimuli appears related to saturation discrimination under conditions of artificial tritanopia. Under conditions of hue substitution, short-wavelength pulses yield good temporal resolution.

Color↗