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PubMed2006

Combining achromatic and chromatic cues to transparency.

We investigated how achromatic and chromatic cues interact to produce transparency. Observers were shown six-region stimulus displays similar to those used by R. Kasrai and F. A. A. Kingdom (2001) and made adjustments of the color and luminance attributes of one of the filter regions to achieve the best percept of transparency. The dependent measure of primary interest was setting reliability, the reciprocal of setting variance. We wished to determine whether the combination of chromatic and achromatic information leads to enhanced reliability of perceived transparency. In Experiment 1, we measured reliability for achromatic, L, superimposed luminance with color, L + C, and superimposed luminance with polarity-reversing color, L + iC. We found that observers' reliability was highest for the L + C condition, consistent with effective cue combination. In a second experiment, we compared setting reliability for L, L + C, and a new chromatic-only condition C. In the L + C condition, observers were asked to make separate and iterative settings of luminance and color to achieve the best percept of transparency. We compared their settings in L with the luminance settings in L + C and their settings in C with their color settings in L + C. Color adjustments were more reliable when accompanied by luminance information but not vice versa. In Experiment 3, we manipulated the transmittance of the achromatic and chromatic filters separately and investigated how this influences the settings made for each attribute. No systematic influence of filter transmittance on the settings made for perceived transparency was found.

Color↗
PubMed2004

Red-green chromatic mechanisms in normal aging and glaucomatous observers.

PURPOSE: This study was designed to determine whether normal aging and glaucoma are associated with red-green (R/G) chromatic processing abnormalities, a function that is primarily performed by the parvocellular visual pathway. METHODS: Chromatic processing mechanisms were examined in 98 glaucomatous observers (between the ages of 49 and 93 years; mean age, 70.8 +/- 9.4 [SD]) and 67 normal observers (between the ages of 49 and 88; mean age, 70.6 +/- 10.6 years) with the use of the minimum-motion and motion-nulling paradigms. Phakic glaucomatous (n = 60; mean age, 68.7 +/- 8.9 years) and normal (n = 32; mean age, 69.8 +/- 10.6 years) and pseudophakic glaucomatous (n = 38; mean age, 74 +/- 9.4 years) and normal (n = 35; mean age, 71.4 +/- 10.6 years) subjects were tested to evaluate the effects of lenticular aging on color perception. RESULTS: Phakic observers (normal or glaucomatous) displayed significantly different minimum-motion values than did both their younger counterparts and all the pseudophakic subjects. These results suggest that normal aging with the presence of a natural lens is accompanied by a significant decrease in green-light sensitivity, an effect that is not exacerbated by glaucoma and is primarily related to optical factors. The data also revealed no differences in color motion perception between groups, indicating that the higher cortical mechanisms of the parvocellular pathway implicated in the analysis of information about the middle and long wavelengths of the visible spectrum are not selectively affected by the disease process and normal aging. CONCLUSIONS: Normal aging and glaucoma do not produce significant R/G chromatic processing deficits at retinal and postretinal levels when optical factors are excluded. The authors propose the hypothesis that glaucoma-related effects on motion perception and blue-on-yellow perimetry should be viewed as evidence of loss of ganglion cells that necessitates integration of information over larger retinal areas and more receptor cells than in the R/G chromatic system. Ganglion cells with large receptive fields involve more neural connections and are less numerous than those that respond to R/G information. The functional consequence of this could be that the loss of a single ganglion cell with a larger receptive field would have a greater impact on visual function than the loss of a ganglion cell with a smaller receptive field, such as the ones that process R/G information. The authors believe that glaucoma-induced functional loss is best viewed as related to receptive field structure and function rather than to anatomic cell-type damage.

Aged↗
PubMed2005

The perception of motion in chromatic stimuli.

The issue of whether there is a motion mechanism sensitive to purely chromatic stimuli has been pertinent for the past 30 or more years. The aim of this review is to examine why such different conclusions have been drawn in the literature and to reach some reconciliation. The review critically examines the behavioral evidence and concludes that there is a purely chromatic motion mechanism but that it is limited to the fovea. Examination of motion performance for chromatic and luminance stimuli provides convincing evidence that there are at least two different mechanisms for the two kinds of stimuli. The authors further argue that the chromatic mechanism may be at a particular disadvantage when the integration of multiple local motion signals is required. Finally, the authors present a descriptive model that may go some way toward explaining the reasons for the differences in collected data outlined in this article.

Color Perception↗
PubMed2006

Chromatic confocal spectral interferometry.

Chromatic confocal spectral interferometry (CCSI) is a novel scheme for topography measurements that combines the techniques of spectral interferometry and chromatic confocal microscopy. This hybrid method allows for white-light interferometric detection with a high NA in a single-shot manner. To the best of our knowledge, CCSI is the first interferometric method that utilizes a confocally filtered and chromatically dispersed focus for detection and simultaneously allows for retrieval of the depth position of reflecting or scattering objects utilizing the phase (modulation frequency) of the interferometric signals acquired. With the chromatically dispersed focus, the depth range of the sensor is decoupled from the NA of the microscope objective.

Journal Article↗
PubMed1993

How surrounds affect chromaticity discrimination.

Chromatic discrimination thresholds were measured with and without surrounds along two cardinal axes of chromaticity space. On one axis the level of short-wavelength-sensitive (SWS)-cone excitation was varied for constant long-wavelength-sensitive (LWS)-cone and medium-wavelength-sensitive (MWS)-cone excitations, and on the other axis there were equal and opposite changes in LWS-cone and MWS-cone excitations for constant levels of SWS-cone excitation. Results for two of three observers showed that with a dark surround, discrimination mediated by SWS cones was regulated by the level of SWS-cone excitation of the starting chromaticity, showing a function with the form of a threshold-versus-radiance function. For an equiluminant white or yellow surround, the discrimination for all three observers showed a minimum at the level of SWS-cone excitation of the surround, giving a V-shaped function for the white surround. An additional experiment with dimmer white surrounds indicated that while the minimum remained at the white point, the function gradually changed toward the shape with a dark surround. Discrimination thresholds mediated by LWS and MWS cones with a dark surround showed a minimum near the LWS-cone excitation of equal-energy white, giving a V-shaped function. The effect of yellow and white surrounds was to deepen the V. The data can be described by a model of chromatic discrimination incorporating a threshold term, a cone gain control, and an opponent gain control into two equations, one for SWS-cone discrimination and one for LWS-cone and MWS-cone discrimination.

Adult↗
PubMed1993

Pigment tests evaluated by a model of chromatic discrimination.

Clinical color-vision tests are evaluated within the framework of a model of chromatic discrimination in terms of cone excitation. The motivation for this study was to derive a method for evaluation of test design, test sensitivity, and observer performance. The discrimination model is based on the assumption that chromatic discrimination is mediated in two independent channels, one for short-wavelength cones and one for long- and middle-wavelength cones. Luminance-dependent templates are derived for each channel, and they describe chromatic-discrimination behavior of the young color-normal observer. The templates incorporate receptor- and opponent-level gain controls. We show how the chromaticities of clinical tests can be calculated in cone-excitation units and how discrimination behavior on the tests can be plotted on the templates. The tests include the Farnsworth-Munsell 100-hue, the Farnsworth Panel D-15, the Farnsworth Panel D-15 desaturated, the American Optical Hardy-Rand-Rittler, the Farnsworth F2 plate, the Standard Pseudoisochromatic Plates, Part II, the Ishihara, and the Minimalist tests. Clinical-test data collected on young color-normal observers at different illumination levels show the validity of the techniques.

Color Perception↗
PubMed1995

Contrast gain control: a bilinear model for chromatic selectivity.

We report the results of psychophysical experiments on color contrast induction. In earlier work [Vision Res. 34, 3111 (1994)], we showed that modulating the spatial contrast of an annulus in time induces an apparent modulation of the contrast of a central disk, at isoluminance. Here we vary the chromatic properties of disk and annulus systematically in a study of the interactions among the luminance and the color-opponent channels. Results show that induced contrast depends linearly on both disk and annulus contrast, at low and moderate contrast levels. This dependence leads us to propose a bilinear model for color contrast gain control. The model predicts the magnitude and the chromatic properties of induced contrast. In agreement with experimental results, the model displays chromatic selectivity in contrast gain control and a negligible effect of contrast modulation at isoluminance on the appearance of achromatic contrast. We show that the bilinear model for chromatic selectivity may be realized as a feed-forward multiplicative gain control. Data collected at high contrast levels are fit by embellishing the model with saturating nonlinearities in the contrast gain control of each color channel.

Adaptation, Ocular↗
PubMed1995

Contributions of neural pathways to age-related losses in chromatic discrimination.

Chromatic-discrimination thresholds were measured for light mixtures lying along individually determined tritan axes and an axis of constant short-wavelength-sensitive- (S-) cone stimulation for 30 color-normal observers (age range 22-77 years). The stimulus was a foveally viewed 2 degrees, circular bipartite field consisting of a standard and a test light. Heterochromatic flicker photometry was used to equate the retinal illuminance of the stimuli at 120 Td for all observers. All stimuli were presented in Maxwellian view. Age-related losses in chromatic discrimination depended on the level of cone stimulation. At relatively lower levels of S- and long-wavelength-sensitive (L-) cone stimulation, discrimination thresholds were elevated for older relative to younger observers. As the level of simulation increased for these two cone types, thresholds converged, on average, for all observers. Application of a model of chromatic discrimination mediated by an S-cone pathway suggests that there is no significant age-related change in Weber fractions and that age-related losses in chromatic discrimination are due, at least in part, to spontaneous neural noise arising in the pathway and/or neural changes that multiplicatively scale all incident light.

Adult↗
PubMed1987

Corresponding chromaticities for different states of adaptation to complex visual fields.

While each of his or her two eyes was independently adapted to a different illuminant in viewing a complex visual field, each of a number of observers matched a series of test colors seen by one eye with a juxtaposed variable stimulus seen by the other eye. The 2 degrees test and matching stimuli were located centrally in the complex adapting field, which subtended an angle of 31 degrees X 24 degrees. In making the matches, the observer viewed the test and matching stimuli for a series of brief intervals (approximately 1 sec) while viewing the complex adapting field with normal eye movements. Nine experiments were performed with different pairs of illuminants and different illuminances ranging from that of an average living room to that of a scene illuminated with hazy sunlight. In three other experiments each of the observer's two eyes was adapted to a different illuminance of D55. The amount of adaptation was more nearly complete at high levels of illuminance than at low levels, and the proportional amount of adaptation was less for the "blue" receptors. When adaptation coefficients were determined from the actual adaptation differences (e.g., from corresponding tristimulus values for matching neutrals) rather than from the adapting illuminants, a linear von Kries transformation based on experimentally determined visual primaries gave corresponding chromaticities that were in good agreement with the results obtained in each of the chromatic-adaptation experiments, except at the lowest illuminances. The results of the experiments in which each eye was adapted to different levels of the same illuminant indicated again that adaptation to the different levels was incomplete, the proportional amount of adaptation being less at low illuminances and for the "blue" receptors. This caused a change in chromatic adaptation with the level of illuminance even when the chromaticities of the adapting lights were equal. The results of these experiments also indicated that higher purities are needed in order to produce the same absolute color appearances at low levels of illuminance.

Color↗
PubMed1991

Achromatizing the human eye: the problem of chromatic parallax.

Attempts to correct the chromatic difference of focus of the human eye will introduce unwanted chromatic parallax if the eye is misaligned with the optical axis of the achromatizing system. Using geometrical optics, we show that the amount of parallax is approximately proportional to the amount of misalignment of the eye, with the constant of proportionality equal to the eye's chromatic difference of refractive error. This prediction was confirmed by the experimental determination of chromatic parallax for two commercially available achromatizing lenses. On the basis of these results, we calculated that anticipated improvements in the polychromatic modulation transfer function of the eye offered by achromatizing lenses will be canceled by approximately 0.4 mm of the misalignment between the lens and the eye. Our prediction that further misalignment would severely reduce image quality of the achromatized eye was verified by psychophysical measurements of contrast sensitivity.

Color Perception↗
PubMed1992

Chromatic and luminance signals in visual memory.

The efficiency of chromatic and luminance signals was studied in a set of tasks requiring the discrimination of two colors. Discrimination was measured around an adapting achromatic light and a number of other points in a three-dimensional color space. As a baseline, discrimination thresholds were measured under conditions permitting a side-by-side comparison of stimuli in space or time. For the spatiotemporal configurations used in these experiments, chromatic signals were more efficient than luminance signals in terms of the difference in cone excitation required at the discrimination threshold. When stimuli were separated in both space and time, so that memory was required for their comparison, the efficiency of luminance signals was attenuated further, while chromatic signals retained their efficiency. Further experiments showed that the addition of a memory requirement did not impair the accuracy of luminance discrimination when the two test colors could be placed in distinct perceptual categories with respect to the surround color. Our results indicate that chromatic signals are particularly efficient in simple color discrimination tasks requiring even the barest amount of memory, especially when the perceptual categorization scheme is not available for the comparison of stimuli.

Adaptation, Ocular↗
PubMed1992

Contrast detection in luminance and chromatic noise.

We measured detection thresholds for a vertically oriented 1.2-cycle-per-degree sine-wave grating embedded in spatiotemporal broadband noise. Noise and signal were modulated in different directions in color space around an equal-energy white point. When signal and noise were modulated in the same direction, we observed a linear relationship between noise spectral density and signal energy at threshold. The slope of this function was the same whether the modulation was along a luminance axis or a red-green axis. If the signal was on one axis and the noise was on the other, no masking was observed. These results support the notion of two independent and equally efficient mechanisms tuned to these directions. We then measured threshold elevations for masks with both chromatic and luminance components. When signal and noise were modulated along the same line (for example, bright red and dark green), thresholds were elevated. When we inverted the phase of the chromatic component of the noise relative to the luminance component (bright green and dark red), the masking effect disappeared, even though the amount of noise in the putative luminance and chromatic mechanisms was exactly the same as before. This implies that detection performance is limited by mechanisms sensitive to both luminance and chromatic contrast signals. We characterized these mechanisms by their spectral tuning curves.

Color Perception↗
PubMed1979

Effects of chromatic targets on a throwing task for subjects referred for learning disability.

The purpose of the study was to determine the effects of chromatic and achromatic targets on performing a throwing task for subjects referred for learning disability. 20 boys referred to the Perceptual Motor Development Center practiced under achromatic or chromatic target conditions. After 5 practice bouts, each subject immediately performed on the opposite condition. When subjects were aware of chromatic and achromatic target alternatives, chromatic targets facilitated performance.

Child↗
PubMed2001

Informational primacy of visual dimensions: specialized roles for luminance and chromaticity in figure-ground perception.

Three experiments were conducted to examine the distinct contributions of two visual dimensions to figure-ground segregation. In each experiment, pattern identification was assessed by asking observers to judge whether a near-threshold test pattern was the same or different in shape to a high-contrast comparison pattern. A test pattern could differ from its background along one dimension, either luminance (luminance tasks) or chromaticity (chromaticity tasks). In each task, performance in a baseline condition, in which the test pattern was intact, was compared with performance in each of several degradation conditions, in which either the contour or the surface of the figure was degraded, using either partial occlusion (Experiment 1) or ramping (Experiments 2 and 3) of figure-ground differences. In each experiment, performance in luminance tasks was worst when the contour was degraded, whereas performance in chromaticity tasks was worst when the surface was degraded. This interaction was found even when spatial frequencies were fixed across test patterns by low-pass filtering. The results are consistent with a late (postfiltering) dual-mechanism system that processes luminance information to extract boundary representations and chromaticity information to extract surface representations.

Attention↗
PubMed1998

Residual processing of chromatic signals in the absence of a geniculostriate projection.

We have investigated the residual processing of chromatic signals in a subject with unilateral damage to the primary visual cortex using psychophysical, pupillometric and functional magnetic resonance imaging (fMRI) methods. Of particular interest was to establish the correlation between the subject's ability to make use of chromatic signals in the blind hemifield to discriminate between different coloured targets, the corresponding residual pupil colour responses and the level and location of cortical activation generated by the same stimuli as revealed by fMRI. The results obtained using the three different experimental approaches are consistent and suggest that retrograde degeneration of thalamic and retinal chromatic processing mechanisms caused by damage to the primary visual cortex in man does not abolish completely the ability to process chromatic signals particularly when large, long-wavelength stimuli are employed.

Journal Article↗
PubMedDate not supplied

[Quantitative criteria for the evaluation of congenital chromatic vision disorders].

The minimum angular size of a color stimulus required for its discrimination has been ascertained to be a quantitative criterion for evaluating the form and degree of congenital chromatic visual diseases. Unlike individuals with normal color perception who distinguish all basic and intermediate colors despite their saturation, anomalous trichromats discriminate more saturated colors with larger angular sizes of stimuli than those with normal color perception. Mild and moderate anomalous trichromats do not discriminate lowly saturated colors or for this they require the angular sizes tens of times greater those for normal trichromats. Persons with severe chromatic visual diseases (Type A) do not distinguish moderately saturated colors either. On recognizing the color of test objects, anomalous trichomats make the most mistakes in perceiving the green and yellow colors, the fewest mistakes in perceiving the red color. The minimum angular sizes required to distinguish colors, the percent of errors in their discrimination, and the range of vision of safety signs depend on the form and degree of congenital chromatic diseases. This makes it necessary to apply a differential approach to providing jobs that require rapid and accurate color discrimination in persons with the protanomalous forms of chromatic pathology.

Adaptation, Physiological↗
PubMed1990

Chromatic, spatial, and temporal losses of sensitivity in multiple sclerosis.

Chromatic, spatial, and temporal losses of sensitivity were measured in 15 eyes of 10 patients with recovered optic neuritis. Chromatic sensitivities (for both red-green and blue-yellow) were measured using color-mixture thresholds; the chromatic sensitivity loss was classified as "selective" if it was significantly greater than the achromatic loss. Spatial and temporal sensitivities were measured with contrast sensitivity functions and flicker modulation sensitivity, respectively; these losses were classified as selective if the losses at high (spatial or temporal) frequencies were significantly greater (or significantly less) than losses at low frequencies. All patients had central fixation and were optically corrected carefully. In 1 eye, selective losses of sensitivity for red-green and blue-yellow were combined with a selective loss of sensitivity at high spatial (but not temporal) frequencies. This type of loss may indicate a selective loss of small axons in the optic nerve. The 8 other eyes that showed significant losses were generally nonselective in their chromatic, spatial, and temporal losses; this may indicate a nonselective loss of small and large axons.

Adult↗
PubMed1988

[The chromatic characteristics of neuronal receptor fields in the visual cortex of the baronduki].

39 orientation-selective neurons and 25 neurons responding to total illumination of the receptive field were investigated by exposing to achromatic and chromatic stimuli. Switching on and off of the bar stationary stimuli has revealed that orientation-selective neurons were not chromatically opponent. But when they were tested by moving chromatic bars, pronounced maximum responses were found either to green (520-540 nm) or to blue (449-458 nm) colours. 7 neurons of 39 were either not activated by exposure to achromatic stimuli of any brightness or were slightly activated. Among 25 neurons responding to total illumination of receptive field, 5 neurons were chromatically opponent. They responded by prolonged tonic activation to the switching on of the green and switching off of the blue stimuli.

Animals↗