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PubMed1999

Selective color constancy deficits after circumscribed unilateral brain lesions.

The color of an object, when part of a complex scene, is determined not only by its spectral reflectance but also by the colors of all other objects in the scene (von Helmholtz, 1886; Ives, 1912; Land, 1959). By taking global color information into account, the visual system is able to maintain constancy of the color appearance of the object, despite large variations in the light incident on the retina arising from changes in the spectral content of the illuminating light (Hurlbert, 1998; Maloney, 1999). The neural basis of this color constancy is, however, poorly understood. Although there seems to be a prominent role for retinal, cone-specific adaptation mechanisms (von Kries, 1902; Pöppel, 1986; Foster and Nascimento, 1994), the contribution of cortical mechanisms to color constancy is still unclear (Land et al., 1983; D'Zmura and Lennie, 1986). We examined the color perception of 27 patients with defined unilateral lesions mainly located in the parieto-temporo-occipital and fronto-parieto-temporal cortex. With a battery of clinical and specially designed color vision tests we tried to detect and differentiate between possible deficits in central color processing. Our results show that color constancy can be selectively impaired after circumscribed unilateral lesions in parieto-temporal cortex of the left or right hemisphere. Five of 27 patients exhibited significant deficits in a color constancy task, but all of the 5 performed well in color discrimination or higher-level visual tasks, such as the association of colors with familiar objects. These results indicate that the computations underlying color constancy are mediated by specialized cortical circuitry, which is independent of the neural substrate for color discrimination and for assigning colors to objects.

Adaptation, Physiological↗
PubMed1987

Observer perception of skin color in a study of malignant melanoma.

Observer perceptions of skin color with a 15-step skin tone panel were evaluated during an as yet unpublished case-control study of malignant melanoma. Skin color is a risk factor for melanoma, and the skin tone panel was introduced in an effort to reduce its misclassification. Reflectances of the 15 artificial skin tones were measured at four wavelengths with a reflectance spectrophotometer. Six observers each evaluated the skin color of eight study subjects twice under three lighting conditions, and the results were transformed to reflectance values. Components of variance analysis demonstrated that between-subject variability contributed 63% or more of the variance at wave-lengths of 400-600 nm, while observers, light source, observation time, and error contributed 30% or less. At 700 nm, only 25.5% of the variance was due to subjects, indicating lower levels of reliability. Similarly, the correlation of visual and spectrophotometric assessment of skin reflectance was higher at 400-600 nm (r = 0.63-0.71) than at 700 nm (r = 0.41). Thus, the value of the skin tone panel-based assessments depends upon knowledge of which wavelengths most closely relate to the physiologic risk factor. For instance, reflectance at 650-700 nm is a better measure of skin melanin content than reflectance at lower wavelengths. Since the role of melanin as a risk factor remains in doubt, the utility of this technique has yet to be demonstrated. However, data from the case-control study and from this validity and reliability study will allow us to develop an analytic approach that minimizes misclassification of skin color as a confounder.

Analysis of Variance↗
PubMed2002

Color opponent neurons in V1: a review and model reconciling results from imaging and single-unit recording.

The signals in visual cortex that ultimately give rise to color perception remain poorly understood. Controversy has particularly surrounded one aspect of color's encoding in the visual system-opponent processing in primary visual cortex. Early single-unit studies suggested that V1 contains relatively few color-opponent neurons. Neuroimaging measurements, however, have suggested that such neurons might be relatively numerous. Here, we reconcile these apparently discrepant results and conclude that V1 contains relatively large numbers of color-opponent neurons. We first review results from each method and find that most neuroimaging studies provide evidence of substantial color opponency in V1, and that despite apparent controversy, most single-unit studies agree that relatively large numbers of V1 neurons show some sort of color opponency. To reconcile the results from different techniques more formally, we used electrophysiological data to predict the outcomes of neuroimaging experiments. We simulated the expected fMRI response in V1 to spatial patterns of different color, based on the neurons' properties, as reported in Johnson, Hawken, and Shapley, (2001). The simulated responses to stimuli used in Engel, Zhang, and Wandell, (1997) agree well with the actually observed fMRI results. The model identifies several factors that led to the apparent discrepancy between techniques, and makes testable predictions about how these factors influence the magnitude of color-opponent signals. fMRI and single-unit data converge to show that large numbers of color-opponent neurons exist in V1.

Color Perception↗
PubMed2001

Color vision deficiencies in Gilles de la Tourette syndrome.

Color perception was tested using the Farnsworth-Munsell 100-Hue Test in a sample of persons with Gilles de la Tourette syndrome (GTS), and compared to norms from three age cohorts in the early second, fourth and sixth decades. Red-green color errors on the Farnsworth-Munsell did not appear to change appreciably as a function of age or GTS. Blue-yellow error scores did, however, increase with age and were exaggerated in the GTS group. It is concluded that sensory and perceptual disturbances are present in GTS as in other basal cell ganglia disorders. The results are discussed in terms of converging retinal dopaminergic mechanisms also associated with Parkinson's and Huntington's diseases and even with normal aging. Suggestions are offered that daily activities and behavior may be affected by spatial and chromatic deficiencies.

Adult↗
PubMed1999

Ratio model for suprathreshold hue-increment detection.

We use psychophysical techniques to investigate the neural mechanisms subserving suprathreshold chromatic discrimination in human vision. We address two questions: (1) How are the postreceptoral detection mechanism responses combined to form suprathreshold chromatic discriminators? and (2) How do these discriminators contribute to color perception? We use a pedestal paradigm in which the subject is required to distinguish between a pedestal stimulus and the same pedestal added to a chromatic increment (the test). Our stimuli are represented in a cardinal space, in which the axes express the responses of the three postreceptoral detection mechanisms normalized relative to their respective detection thresholds. In the main experiment the test (a hue increment) was fixed in the direction orthogonal to the pedestal in our cardinal space. We found that, for high pedestal contrasts, the test threshold varied proportionally with the pedestal contrast. This result suggests the presence of a hue-increment detector dependent on the ratio of the outputs from the red-green and blue-yellow postreceptoral detection mechanisms. The exception to this was for pedestals and tests fixed along the cardinal axes. In that case detection was enhanced by direct input from the postreceptoral mechanism capable of detecting the test in isolation. Our results also indicate that discrimination in the red-green/luminance and blue-yellow/luminance planes exhibits a behavior similar to discrimination within the isoluminant plane. In the final experiment we observed that thresholds for hue-increment identification (e.g., selecting the bluer of two stimuli) are also governed by a ratio relationship. This finding suggests that our ratio-based mechanisms play an important role in color-difference perception.

Adult↗
PubMed2002

Stereo disparity improves color constancy.

Binocular disparity is an aspect of natural viewing. This research investigates whether disparity affects surface color perception. Achromatic settings were obtained and compared for two stereograms of a scene with specular reflections, one stereogram with binocular disparity and one without it (cyclopean view). Binocular disparity was found to improve color constancy. Next, the geometry of specular highlights, which is distorted without binocular disparity, was specifically examined. Measurements compared color constancy with specular reflections that were either normal (with stereo disparity) or distorted (cyclopean view of the specularities). No significant change in constancy was found due to the geometrical distortion of specular highlights that occurs without stereo disparity, suggesting that constancy depends on other features of the percept affected by disparity. The results are discussed in terms of illuminant estimation in surface color perception.

Color Perception↗
PubMed2003

Color vision.

Color vision starts with the absorption of light in the retinal cone photoreceptors, which transduce electromagnetic energy into electrical voltages. These voltages are transformed into action potentials by a complicated network of cells in the retina. The information is sent to the visual cortex via the lateral geniculate nucleus (LGN) in three separate color-opponent channels that have been characterized psychophysically, physiologically, and computationally. The properties of cells in the retina and LGN account for a surprisingly large body of psychophysical literature. This suggests that several fundamental computations involved in color perception occur at early levels of processing. In the cortex, information from the three retino-geniculate channels is combined to enable perception of a large variety of different hues. Furthermore, recent evidence suggests that color analysis and coding cannot be separated from the analysis and coding of other visual attributes such as form and motion. Though there are some brain areas that are more sensitive to color than others, color vision emerges through the combined activity of neurons in many different areas.

Animals↗
PubMed1989

Effects of viewing conditions on standard measures of acquired and congenital color defects.

We examined the effect of variations in viewing distance and viewing duration on the performance of color-normal observers with four standard tests of color vision. Significant effects of the experimental manipulations were obtained: both increasing viewing distance and decreasing viewing duration significantly increased the number of errors made by observers. Moreover, the four tests differed widely in their sensitivity to the variations in viewing conditions. Practical implications of the findings for the administration and selection of plate tests are discussed, and possible mechanisms underlying the results are suggested.

Color Perception↗
PubMed1999

Research note: a multidimensional scaling comparison of color metrics for response times and rated dissimilarities.

Individual-differences multidimensional scaling was applied to a set of proximity data for equiluminant lights (Paramei & Cavonius, 1999) to explore any differences between two data collection procedures (rated dissimilarities, and same/different response times [RTs]), as well as between color-normal and abnormal observers. Two conclusions emerged: (1) The pattern of similarities from observers with anomalous color vision can be understood in terms of a compressed color plane (the weighted Euclidean model of individual differences); and (2) there is evidence that the color "plane" is either curved or governed by a non-Euclidean distance function. When color-normal observers are examined in the weighted-Euclidean framework, minor differences emerge between RT and rating data. But the main distinguishing feature of RT data is a pattern of decreasing accuracy for larger color distances. This must be taken into account, since it can itself induce curvature.

Color Perception↗
PubMedDate not supplied

Multidimensional scaling of D15 caps: color-vision defects among tobacco smokers?

Tobacco smoke contains a range of toxins including carbon monoxide and cyanide. With specialized cells and high metabolic demands, the optic nerve and retina are vulnerable to toxic exposure. We examined the possible effects of smoking on color vision: specifically, whether smokers perceive a different pattern of suprathreshold color dissimilarities from nonsmokers. It is already known that smokers differ in threshold color discrimination, with elevated scores on the Roth 28-Hue Desaturated panel test. Groups of smokers and nonsmokers, matched for sex and age, followed a triadic procedure to compare dissimilarities among 32 pigmented stimuli (the caps of the saturated and desaturated versions of the D15 panel test). Multidimensional scaling was applied to quantify individual variations in the salience of the axes of color space. Despite the briefness, simplicity, and "low-tech" nature of the procedure, subtle but statistically significant differences did emerge: on average the smoking group were significantly less sensitive to red-green differences. This is consistent with some form of injury to the optic nerve.

Color Perception↗
PubMedDate not supplied

Measuring short-wavelength-sensitive cone discrimination thresholds using pseudoisochromatic figures displayed on a color monitor.

PURPOSE: To simplify the testing of short-wavelength-sensitive (SWS) cone function in the clinic. METHODS: SWS-cone discrimination thresholds were measured along the tritan axis using pseudoisochromatic figures displayed on a color monitor. A circular 6 degrees field, containing spatially discrete patches of varying sizes and luminances, was presented on a background. A subset of patches formed the target patch in the shape of a C. Eight subjects with normal color vision reported the direction of the gap in the C using a cursor controlled by a joystick. DATA: were expressed in units of SWS-cone trolands. RESULTS: SWS-cone discrimination threshold increased slowly as the SWS-cone trolands of the starting chromaticity increased. The dependence of the threshold on the SWS-cone activation level was similar to literature reports of chromatic discrimination measured with conventional paradigms. CONCLUSIONS: The advantages of this method: (a) It is a simple intuitive task for patients. (b) The paradigm can be implemented with an 8-bit/gun color monitor. (c) The test avoids the need to define equiluminance for the individual patient before the color test is administered. This method can provide a useful technique for measuring SWS-cone function in a clinical population.

Adult↗
PubMedDate not supplied

The effect of test distance on the CN lantern results.

The purpose of this study is to determine how the viewing distance affects the pass/fail results of the CN Lantern (CNLan). The CNLan is a color vision test designed for the railway industry. It presents 15 triplets of colored lights that could be any combination of red, green and yellow. The test was viewed from 4.6 m and 2.3 m. Sixty-seven color-defectives participated in the first part of the study. Sixty-six percent of the subjects repeated the experiment 10 days later. There was a significant (P < 0.05) decrease in the mean number of errors from 7.6 to 4.3 as the distance decreased. There was also a corresponding increase in the percentage of subjects who passed from 9.0% at 4.6 m to 20.9% at the 2.3 m viewing distance. None of the subjects who passed at the longer distance failed at the shorter distance. The replication results were statistically identical to the first session (P > 0.05). Decreasing the CNLan viewing distance by 50% does decrease the number of errors and increase the pass rate. This indicates that some color-defectives could work in the railway yards where the sighting distances for the signal lights are shorter than on the main track.

Color Perception↗
PubMed1985

Retinal toxicity after high-dose cisplatin therapy.

Because of increasing complaints of visual dysfunction, 13 patients with refractory or recently diagnosed ovarian carcinoma were evaluated for possible cisplatin-induced ophthalmologic toxicity. All patients had received high-dose cisplatin (200 mg/m2 in five divided daily doses) over two to four cycles. Eight patients (62%) developed symptoms of blurred vision and three (23%) also developed altered color perception. Retinal toxicity in the form of cone dysfunction was documented by electroretinography and color vision testing in 11 patients. Three patients were studied prospectively. Two patients who developed cone dysfunction had normal ophthalmologic exams before the initiation of chemotherapy or after one cycle of cisplatin, suggesting a causal relationship between cisplatin therapy and subsequent retinal abnormalities. Though visual acuity improved off therapy, color vision abnormalities persisted as long as 16 months beyond therapy.

Adult↗
PubMed1997

Color vision defect type and spatial vision in the optic neuritis treatment trial.

PURPOSE: To describe the types of color vision defects present in the acute phase of the disease and 6 months into recovery in the 438 participants of the Optic Neuritis Treatment Trial. METHODS: Patients meeting strict eligibility criteria were seen within 8 days of the onset of symptoms and then at regular follow-up visits. At the first and 6-month visits (and subsequent annual visits), spatial vision (acuity, contrast sensitivity), visual fields, and color vision were measured. Farnsworth-Munsell 100-hue tests were scored by a variant of the method of quadrant analysis described by Smith et al (Am J Ophthalmol. 1985; 100:176-182). RESULTS: Most persons show mixed red-green (RG) and blue-yellow (BY) color defects (one type predominating, accompanied by a lesser defect of the other type). BY defects tend to be slightly more common in the acute phase of the disease, with slightly more RG defects at 6 months. Persons may shift defect type over time. Defect type was not related to any of the spatial vision measures at either test time or to treatment group; however, severity of color defect was related to both spatial vision measures and treatment group. CONCLUSIONS: Contrary to common clinical wisdom, optic neuritis is not characterized by selective RG defects. Color defect type cannot be used for differential diagnosis of optic neuritis.

Acute Disease↗