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The dilemma of color deficiency and art.

No "major" painter is known to be color deficient. Are there truly no color deficient artists, or have they not been recognized? The historical literature cites criteria for recognizing color deficiency in artists, but they are hard to apply without knowing the intentions of an artist. The work and commentary of a color-deficient artist who works currently in Paris are presented as an example. He uses a limited palette of colors, based on advice from colleagues as much as his own perceptions, and he uses colors in ways that do not always fit with expectations for color deficiency. Biographies of earlier painters suggest that there were a few whose color sense was poor, but these painters used assistants to help. The color sense of others, such as the English landscape painter John Constable (1776-1837), has been questioned because of a preponderance of suspicious color, such as murky green. However, there are good reasons to doubt that Constable was color deficient. It is instructive to know how proven color deficiency has influenced an artist's style. When medical information is unavailable, the best advice for the diagnostically-inclined observer is just to enjoy the art.

Color Perception↗

PubMed2000

Tritanopic color matches and the middle- and long-wavelength-sensitive cone spectral sensitivities.

Tritanopic color matches (i.e. matches that depend on the middle- (M) and long- (L), but not short- (S) wavelength-sensitive cones) were made between two half-fields: one illuminated by either a 405 or a 436 nm Hg spectral line; the other by a light of variable wavelength and radiance. Our purpose was to test between rival M- and L-cone spectral sensitivities, which should predict the tritanopic matches. The observers were tritanopes, in whom functioning S-cones are lacking, or normal trichromats, in whom artificial tritanopia was induced by a strong, violet adapting field. The wavelengths found to match the 405 and 436 nm lights agreed poorly with those predicted by the cone spectral sensitivities of Smith and Pokorny (1975) [Vision Research, 15, 161], while the 405 nm matching wavelength agreed poorly with that predicted by Stockman, MacLeod and Johnson (1993) [Journal of the Optical Society of America, A10, 2491]. Both matching wavelengths agreed well, however, with the predictions of the Stockman and Sharpe (2000) [Vision Research] M- and L-cone spectral sensitivities, which lie within the range of measured matches.

Color Perception↗

PubMed2000

The spectral sensitivities of the middle- and long-wavelength-sensitive cones derived from measurements in observers of known genotype.

The spectral sensitivities of middle- (M-) and long- (L-) wavelength-sensitive cones have been measured in dichromats of known genotype: M-cone sensitivities in nine protanopes, and L-cone sensitivities in 20 deuteranopes. We have used these dichromat cone spectral sensitivities, along with new luminous efficiency determinations, and existing spectral sensitivity and color matching data from normal trichromats, to derive estimates of the human M- and L-cone spectral sensitivities for 2 and 10 degrees dia. central targets, and an estimate of the photopic luminosity function [V(lambda)] for 2 degrees dia. targets, which we refer to as V(2)*(lambda). These new estimates are consistent with dichromatic and trichromatic spectral sensitivities and color matches.

Adult↗

PubMed2001

Study of colour discrimination with comb-filtered spectra.

Techniques that involve the use of comb-filtered spectra to study human colour vision have been developed in previous work (Bonnardel, V., Bellemare, H., Mollon, J.D., 1996. Measurements of human sensitivity to comb-filtered spectra, Vision Research 36, 2713-2720; Bonnardel, V., Ruderman D.L., Barlow, H.B., 1997. A fast determination of the Spectral Modulation Sensitivity Function: a comparison between trichromats and deuteranopes. In: C.R. Cavonius (ed.), Color vision deficiencies XIII. Dordrecht: Kluver 415-424). These techniques are applied in the present study to measure colour discrimination among deuteranomalous observers and normal trichromats, with the aim of determining the spectral position of the anomalous cone fundamentals. Results show that comb-filtered spectra are useful in determining the extent to which variability in colour discrimination among anomalous and normal trichromatic colour observers is accounted for by the spectral properties of photoreceptors.

Color Perception↗

PubMed2002

Variations in long- and middle-wavelength-sensitive opsin gene loci in crab-eating monkeys.

We analyzed variations in long (L)- and middle (M)-wavelength-sensitive opsin gene loci in crab-eating monkeys. Unlike humans, most monkeys have a single L and a single M gene. Two variant genotypes, one with only one opsin gene (dichromatic) and one with tandemly arrayed multiple genes, were also found in the monkeys. However, the frequency of the former was 0.47%, and that of the latter was 5% in the monkeys, while 2% and 66%, respectively, in Caucasian males. The two variants were found only in Java Island, Indonesia, and South Thailand, respectively. The data suggest that the frequency of each genotype is different among Old World primates.

Animals↗

PubMed2003

Colour thresholds in dichromats and normals.

Studies indicate dichromats detect large, long duration spectral increments presented on bright white backgrounds with a blue-yellow colour opponent mechanism. Since opponent processes signal colour, we hypothesized that under these viewing conditions dichromats should perceive spectral increments as coloured at detection threshold. Psychophysical detection and colour discrimination thresholds were determined for normal and dichromatic humans. Test stimuli were 2 degrees, 200 ms increments presented upon a white, 1000 td, spatially coincident background. As expected, normal observers were able to discriminate between white and spectral flashes at intensities near detection threshold intensities. Dichromatic observers required suprathreshold ( approximately 0.30 log units) stimulus intensities to discriminate between the white and spectral flashes. The results do not support our hypothesis and alternative explanations for the elevated colour discrimination thresholds in dichromats are discussed.

Adult↗

PubMed2003

Wavelength dependence of the optomotor response in zebrafish (Danio rerio).

The action spectrum of motion detection in zebrafish (Danio rerio) was measured using the optomotor response in the light adapted state. The function has a single maximum at 550-600 nm, and is similar to the spectral sensitivity function of the L-cone type in the mid and long wavelength range. At shorter wavelengths the values of three of the five fish tested are lower. As in goldfish [Vis. Res. 36 (1996) 4025], the result indicates a dominance of the L-cone type with an inhibitory influence of M- or S-cones. Experiments with a red/green striped cylinder showed that the optomotor response was at minimum whenever the L-cone type was not modulated by the moving pattern. This demonstrates that motion vision in zebrafish is "color blind", using mainly one of the four cone types probably involved in color vision.

Animals↗

PubMed1997

Shift of equiluminance in congenital color vision deficiencies: pattern-ERG, VEP and psychophysical findings.

We compared electrophysiological responses [pattern-ERG (PERG) and VEP] and psychophysical measures to color stimuli to separate different forms of anomalous color vision. PERG and VEP were recorded from seven normals and 14 subjects with congenital color vision deficiencies. Stimuli were color checkerboards with 0.5 deg check size, phase reversing at 34 rev/sec. The luminances of the red and green parts were varied in opposite direction from 0 to 30 cd/m2, while the hue of individual squares and space-averaged luminance were held constant. This allowed for one equiluminance condition where flicker appeared fused. In the seven normals, the subjective equiluminance was reached at a luminance ratio red/(red + green) = 0.50-0.53. At that point, the PERG amplitude was moderately, and the VEP amplitude sharply reduced. In 14 color anomalous subjects both the PERG and VEP were sharply reduced at equiluminance. These dips were shifted compared to normals and the dip position corresponded to the predicted luminance ratios obtained by calculations from L- and M-cone activation using the Smith-Pokorny transformation. As we found a close correlation of the VEP-dip position and the anomalous quotient, these electrophysiological measures may allow objective assessment of color vision deficiencies.

Adult↗

PubMed1997

The visual photopigments of simple deuteranomalous trichromats inferred from color matching.

Deuteranomalous trichromacy is the most common form of inherited color-vision deficiency. A modern description of its cause is a single abnormality: the normal middle-wave cone photopigment (M) is replaced by a shifted middle-wave pigment (M) that is shared by all deuteranomalous trichromats. This explanation, however, fails to account for the individual differences in color vision observed even within the sub-group of deuteranomals with good chromatic discrimination. An ensemble of color matches is used here to test whether these individual differences reflect differences in the wavelength of peak sensitivity (lambda max) of individual deuteranomals' cone photopigments. The results show variation in both the lambda max and the effective optical density of their cone pigments. The individual differences found in lambda max are in accord with recent molecular biological research that shows individual differences in the genes thought to encode deuteranomalous photopigments.

Adult↗

PubMed1997

Hepatic retinopathia. Changes in retinal function.

In patients suffering from hepatic failure, the brain is subject to defined morphological and functional changes known as hepatic encephalopathia (HE). The morphological changes are dominated by glial cells (Alzheimer-type II astrocytes). It has recently been possible to demonstrate, that the retinal glia (Müller) cells undergo similar morphological changes. The present study was carried out in order to reveal if these Müller cell changes cause any characteristic functional deficits. We examined 11 patients with different stages of HE due to liver cirrhosis. Six patients were at stage 0 or 1 (group I) and five at stage 2 or 3 (group II). They underwent ophthalmological routine examination, colour vision testing and standard ERG recording. None of the patients reported impaired vision, in daylight or at night. There were no fundus abnormalities except very mild changes of the pigment epithelium and abnormal reflexes of the inner limiting membrane, especially in the higher HE stages. The number of confusions in the colour arrangement test increased with the higher stages of HE, preferably in the tritan axis. The scotopic a- and b-waves of the electroretinogram (ERG) were almost unchanged in group I and significantly decreased and delayed in group II. The photopic ERG b-wave amplitudes were changed in a similar fashion. Oscillatory potentials proved to be most sensitive to hepatotoxic changes. Their latencies were significantly delayed even in group I. Amplitudes were decreased significantly only in group II. Patients suffering from hepatic failure and accompanying HE display functional abnormalities of the retina. These are best demonstrated by the ERG, and correlate well with the degree of HE. A hypothesis is presented that relates the observed functional changes to altered neurotransmitter levels and impaired retinal glial-neuronal interaction, due to Müller cell damage caused by elevated ammonia levels.

Adult↗

PubMed1997

Rayleigh match ranges of red/green color-deficient observers: psychophysical and molecular studies.

Large-field Rayleigh match ranges were measured in 27 red/green color-deficient male observers, using bright, temporally alternating, 3-9 deg annular test fields. The observers' X-linked opsin gene arrays were characterized by molecular genetic techniques, and used to infer the absorption maxima of each observer's L and/or M cone photopigment(s). Measured match ranges decreased rapidly as the inferred separation in pigment absorption maxima increased from 0 to 2-3 nm, and varied irregularly thereafter. Following He & Shevell [(1995) Vision Research, 35, 2579-2588] predicted match ranges were calculated for various pigment separations and assumed values of pigment optical density. The predicted variations in match range encompassed the measured match ranges of most (but not all) of the color-deficient observers. The calculations also showed that differences in pigment optical density, in two cone types containing the same pigment, are sufficient to allow a moderate degree of chromatic discrimination. Such models thus provide a possible account of the fact that some color-deficient observers, with only a single X-linked opsin gene, can make red/green chromatic discriminations.

Adolescent↗

PubMed1997

Comparison of red-green, blue-yellow and achromatic losses in glaucoma.

Achromatic losses in glaucoma would be expected to be greater than, or equal to, red-green chromatic losses if the following assumptions are made: (1) the function of the remaining axons is either unchanged or non-selectively reduced; (2) red-green chromatic information is signaled by the midget ganglion cell system; and (3) the function of the magnocellular system is reduced at least as much as that of the midget ganglion cells. This prediction was tested by measuring red-green (along with blue-yellow) mixture thresholds for 1 deg, 0.2 sec test spots presented on a color monitor on a white background of 50 cd/m2. Ellipses were fitted to plots of green contrast as a function of red contrast (or yellow as a function of blue), and major and minor axes of these ellipses were taken as measures of chromatic and achromatic thresholds, respectively. The study population consisted of 29 eyes in 29 patients with early glaucoma; control data were derived from a data bank of 83 normal eyes. Red-green losses were significantly (P < 0.05) greater than achromatic losses in 6 out of the 11 eyes which showed significant losses of either chromatic or achromatic sensitivity (or both). It is concluded that, for these eyes, at least one of the above three assumptions is incorrect.

Adult↗

PubMed1997

Parallel increase of heterochromatic increment threshold and postadaptation thresholds in Parkinson's disease and in neuroleptic treatment.

Following reports on a predominant loss of blue/yellow contrast sensitivity in Parkinson's disease, we revisited the physiological phenomenon of transient tritanopia. Normative data were collected from 33 healthy individuals using different colour and time combinations. Stimuli of 440 nm wavelength (blue) proved optimal, if flashed for 50 msec within the early phase of a 2 sec pause in the 600 nm adaptation light. These conditions were then applied to 15 patients with Parkinson's disease. We found a parallel increase of increment threshold (P < 0.001) and postadaptation thresholds (P < 0.01), with little change in the extent of transient tritanopia. The same tendency at a lower significance level was found in 15 psychiatric patients under chronic treatment with depot neuroleptics.

Adaptation, Ocular↗

PubMed1998

The contribution of color to visual memory in X-chromosome-linked dichromats.

We used a recognition memory paradigm to assess the visual memory of X-chromosome-linked dichromats for color images of natural scenes. The performance of 17 protanopes and 14 deuteranopes, who lack the second (red-green opponent) subsystem of color vision, but retain the primordial (yellow-blue opponent) subsystem, was compared with that of 36 color normal observers. During the presentation phase, 48 images of natural scenes were displayed on a CRT for durations between 50 and 1000 msec. Each image was followed by a random noise mask. Half of the images were presented in color and half in black and white. In the subsequent query phase, the same 48 images were intermixed with 48 new images and the subjects had to indicate which of the images they had already seen during the presentation phase. We find that the performance of the color normal observers increases with exposure duration. However, they perform 5-10% better for colored than for black and white images, even at exposure durations as short as 50 msec. Surprisingly, performance is not impaired for the dichromats, whose recognition performance is also better for colored than for black and white images. We conclude either that X-chromosome-linked dichromats may be able to compensate for their reduced chromatic information range when viewing complex natural scenes or that the chromatic information in most natural scenes, for the durations tested, is sufficiently represented by the surviving primordial color subsystem.

Adult↗

PubMed1998

Scotopic vision in colour-blinds.

Alleles causing colour-blindness are present in humans at non-negligible levels, and it is not yet understood how colour-blindness is maintained, since colour-vision probably provides a selective advantage, e.g. when foraging. We show that after dark-adaptation colour-blinds had lower light perception thresholds than colour-normals (0.44 log-units), which may give a selective advantage under scotopic conditions, which may offset the disadvantage that colour-blinds suffer during foraging.

Color Vision Defects↗

PubMed1998

Dichromacy characterized by chrominance planes.

Dichromacy is described in terms of dichromatic opponent colour spaces. By means of the perceptual criteria 'equally bright', 'neither blue nor yellow' and 'neither red nor green' and embedding in a three-dimensional colour space, it is possible for each type of dichromat to quantify a null-chrominance plane and a null-luminance plane, both of which intersect in the missing colour. These two null planes (or the trace of their intersection with the chromaticity chart) are the chromaticities of the dichromatic opponent primaries. Since a null-luminance plane contains only colour ('chrominance'), it is simply a chrominance plane. Under the assumption that the retinal short-wavelength cones do not contribute to luminance, the chrominance planes of the three types of dichromats intersect in a common straight line, the 'blue' fundamental primary vector. This constellation may serve as a general characterisation of dichromacy.

Color↗

PubMed1998

Is the rod visual field temporally homogeneous?

Cone vision has been shown to be temporally inhomogeneous across the visual field. In the periphery, contrast sensitivity is lower for low temporal frequencies and higher for high temporal frequencies. Here we ask a similar question for rod vision at mesopic luminances. Isolation is obtained by testing a well documented rod monochromat. We show that the rod visual field exhibits only a modest degree of temporal inhomogeneity.

Color Vision Defects↗

PubMed1998

Temporal analysis of the chromatic flash VEP--separate colour and luminance contrast components.

Temporal analysis of the chromatic flash visual evoked potential (VEP) was studied in human subjects with normal and anomalous colour vision using a deterministic pseudo-random binary stimulus (VERIS). Five experiments were carried out on four normal subjects investigating heterochromatic red-green exchange and single colour/achromatic (either red/grey or green/grey) exchange over a wide range of luminance ratios for the two stimuli, the effects of lowered mean luminance on the chromatic VEP and the effects of colour desaturation at constant mean luminance and constant luminance contrast. Finally, the performance of three dichromats, a protanope and two deuteranopes, on heterochromatic exchange VEP and on colour desaturation were investigated. In contrast to the chromatic electroretinogram, which shows great symmetry with respect to luminance ratio on opposite sides of the isoluminant point, the chromatic VEP demonstrated a distinct asymmetry when the colours exchanged included red. On the red side of isoluminance (red more luminant than green), a wave with longer latency and altered waveform became dominant. The effects of green stimulation were indistinguishable from those of achromatic stimulation at the same luminance contrast over the whole range of chromatic contrast and for all levels of desaturation studied. Desaturation of red with constant luminance contrast (desaturated red/grey stimulation) resulted in a systematic alteration in the evoked waveform. Subtraction of the achromatic first- and second-order responses from responses recorded in the red desaturation series resulted in remarkably uniform waveforms, with peak amplitudes growing linearly with saturation. The absence of interaction between achromatic and coloured components for all (including the most intense colour) stimulus parameters used suggests that the generators of these components are separate. Recordings from the dichromats showed that the contrast response minimum shifted from the point of photopic isoluminance to the point of zero cone contrast (at the silent substitution point) for the remaining cone type. The waveforms recorded with a series of luminance ratios were much simpler than those recorded from trichromats and symmetrical with respect to their isoluminant points. Despite the indication of the presence of L cones of apparently normal spectral sensitivity in the deuteranopes (on the basis of flicker photometry), there was no evidence for a red-sensitive component in the desaturation or heterochromatic stimulation series. The results are discussed in terms of the possibility of separate generation of chromatic and achromatic contributions to the VEP.

Color Perception↗