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PubMed1999

Evidence for the stochastic independence of the blue-yellow, red-green and luminance detection mechanisms revealed by subthreshold summation.

We investigated the manner in which the outputs of the three postreceptoral mechanisms (red-green, blue-yellow and luminance) combine to determine contrast threshold. We used a subthreshold summation paradigm to test whether the combination of the postreceptoral mechanism outputs could be described by a probability summation model which assumes stochastic independence of the mechanisms, and determined the best fitting summation exponent. Stimuli were Gaussian enveloped 1 c/d sinusoidal gratings represented in a 3D cardinal space transformed from cone contrast axes, and normalized to detection threshold. The use of this space avoids the presence of elongated threshold contours, allowing a reliable model fit to include the less sensitive blue-yellow and luminance mechanisms. Our results were well fitted by the probability summation model and hence support the underlying stochastic independence of the three postreceptoral mechanisms.

Chi-Square Distribution↗
PubMed1999

The spatial tuning of color and luminance peripheral vision measured with notch filtered noise masking.

We have measured the spatial bandwidths of the bandpass red-green chromatic and luminance mechanisms at four locations in the nasal visual field (0, 10, 20 and 30 degrees) using a method of notch filtered noise masking which effectively removes the artifact of off-frequency looking for our stimuli. Detection thresholds were measured for luminance or isoluminant red-green Gaussian enveloped test gratings of 0.5 cpd embedded in 1/f noise. Firstly, thresholds were obtained as a function of increasing noise spectral density and were fitted using a standard noise masking model. These results support the existence across the visual field of independent, red-green chromatic and luminance mechanisms with similar sampling efficiencies. Secondly, we measured thresholds in notch filtered noise as a function of notch width and derived the spatial bandwidth of the detection mechanism. We find both color and luminance mechanisms have similar bandwidths which remain virtually constant across eccentricity. These results indicate strong overall similarities between the early processing of color and luminance vision, and lend support to the role of color as an 'intrinsic image' in spatial vision. The results are discussed in the light of the anchored channel and shifting channel models of peripheral contrast sensitivity and pattern detection.

Color Perception↗
PubMed1999

Effect of the tuberculostaticum ethambutol and stimulus intensity on chromatic discrimination in man.

In goldfish it has been shown that ethambutol shifts the threshold for wavelength discrimination without affecting the absolute sensitivity of the cones. In this study we demonstrate that a similar colour vision disturbance occurs in tuberculosis patients treated with ethambutol. After 2 months of ethambutol treatment, chromatic discrimination was measured with a computerized forced two choice (CD) test with isoluminant coloured stimuli and with three other colour vision tests: the Ishihara, the Oscar and the Lanthony Desaturated 15 Hue tests. The scores of the patient group (n = 19) on these four colour vision tests were compared with the scores of a group of control subjects (n = 33) and a group of congenital red/green colour-blind subjects (n = 5). A reduction of the stimulus intensity of 1 log unit caused a significant reduction in red/green chromatic discrimination, measured with the CD test in both, control subjects and patients. This intensity dependent reduction was significantly greater for patients than for controls. In this respect, man and goldfish behave similarly. Furthermore, the CD test showed the same ethambutol-induced reduction in chromatic discrimination at low intensity for the blue/green part of the spectrum. This has not been measured in goldfish. The origin of this ethambutol-induced colour vision disturbance must be at a post-photoreceptor site, because the Ishihara and Oscar tests, both designed to screen for photoreceptor-based, or primary red/green colour vision disturbances, did not discriminate between patients and control subjects. Thus, as in goldfish, we find that in patients ethambutol shifts the threshold for chromatic discrimination without changing the absolute sensitivity.

Adolescent↗
PubMed1996

Visual outcome in bilateral nonarteritic anterior ischemic optic neuropathy.

BACKGROUND: Nonarteritic anterior ischemic optic neuropathy (NAION) is a common cause of visual loss in the older population. Bilateral NAION is a well-documented entity; however, no study to date has compared the visual outcome between affected eyes. METHODS: The authors retrospectively reviewed the charts of 99 patients with diagnoses of NAION over 3 1/2 years. In the 23 patients with bilateral involvement, 16 were included in the study for analysis of final visual outcome between affected eyes. Snellen acuity, Ishihara color plates, and Humphrey automated perimetry were evaluated as the parameters of visual function. Descriptive analysis of the outcome between affected eyes for each parameter is presented as a frequency distribution of pre-defined groups. Statistical significance is established using nonparametric tests. RESULTS: Bilateral NAION was found in 23% (23/99) of the patients studied. The authors identified a high percent agreement between eyes with regard to visual acuity (81% within 3 Snellen lines), color vision (69% within 3 plates), and Humphrey visual field (75% within 5 decibels of mean deviation). Additionally, there was a statistically significant correlation between affected eyes for all three visual parameters: visual acuity (P = 0.043), color vision (P = 0.001), and Humphrey visual field (P = 0.039). CONCLUSION: The authors found a high percent agreement and statistically significant correlation in final outcome between affected eyes of patients with bilateral NAION for visual acuity, color vision, and visual field loss. With a larger series, it may be possible to predict the visual outcome of the second affected eye based on the parameters of the first eye.

Adult↗
PubMed2002

Color vision and occupational chemical exposures. II. Visual functions in non-exposed subjects.

This paper presents data on visual functions (visual acuity, contrast sensitivity, and several tests of color vision), in a group of 199 non-exposed healthy subjects with an even distribution over the age range 18-65 years, and sex. Although subjects with obvious congenital color vision deficiencies were removed from the analyses (four males), females were superior to males on several of the color vision tests applied. Age influenced visual acuity and contrast sensitivity, while color discrimination was less affected. Correlations between functions of the right and the left eye in the individual subjects were rather low, ranging from 0.40 to 0.73. Correlations between visual acuity and contrast sensitivity on the one hand and color discrimination ability on the other hand were still lower (r < 0.20). These low correlations between functions in the two eyes support the need for testing each eye separately.

Adolescent↗
PubMed2001

Color vision after laser in situ keratomileusis.

PURPOSE: To evaluate the effect of laser in situ keratomileusis (LASIK) on color vision. SETTING: Department of Ophthalmology, China Medical College Hospital, Taichung, Taiwan. METHOD: This prospective study comprised consecutive patients having LASIK. Patients were eligible for inclusion if they had a best corrected visual acuity of 20/20 or better and a normal color vision test preoperatively and an uncorrected near visual acuity of 20/40 or better postoperatively. Color vision was tested using the Farnsworth-Munsell 100-hue test (FM 100 test) preoperatively and 1 day, 1 week, and 1 month postoperatively. RESULTS: Twenty-nine eyes of 15 patients having LASIK were enrolled in the study. The mean patient age was 29.2 years +/- 2.9 (SD). The mean preoperative spherical equivalent refractive error was -5.6 +/- 1.8 diopters, and the mean preoperative error score of the FM 100 test was 3.79 +/- 1.55. After surgery, no significant change in the error score was observed at 1 day (4.30 +/- 1.07, P =.1039, paired t test), 1 week (3.72 +/- 1.25, P =.8125, paired t test), or 1 month (3.97 +/- 1.29, P =.6149, paired t test). CONCLUSION: Laser in situ keratomileusis did not affect color vision evaluated by the FM 100 test.

Adult↗
PubMed1996

Color vision in patients with a silicone intraocular lens.

PURPOSE: To test color vision in eyes with a silicone intraocular lens (IOL) and compare it with that in normal phakic eyes. SETTING: University Eye Clinic of Kuopio, Finland. METHODS: Color vision in 33 patients from 50 to 69 years old with a silicone IOL was evaluated with the Farnsworth-Munsell 100 hue test (FM 100) and the Color Vision Meter 712 (CVM) anomaloscope. In the FM 100 test, 37 normal phakic eyes served as controls; 21 were 50 to 59 years old and 16, 60 to 69 years old. In the CVM, 46 normal phakic eyes served as controls; 21 were 50 to 59 years old and 25, 60 to 69 years old. Nine of the 33 patients had a silicone IOL in one eye and a poly(methyl methacrylate) (PMMA) IOL in the other; the color vision in the two eyes was compared. RESULTS: The FM 100 results showed no significant difference between the silicone IOL and control eyes. In the CVM examination, the blue equation showed a significantly greater shift to the green side (patient sees more blue) in the silicone IOL group than in the control group. Other CVM results were similar between groups. No significant difference was found in any test between the 9 PMMA IOL eyes and the contralateral silicone IOL eyes. CONCLUSION: Eyes with a silicone IOL had color discrimination ability similar to that of normal phakic eyes. In the blue color sensitivity test, the silicone IOL eyes had significantly better results. There were no significant differences between eyes with a silicone IOL and contralateral eyes with a PMMA IOL.

Aged↗
PubMed1999

Assessment of potential macular function using a color saturation discrimination test in eyes with cataract.

PURPOSE: To study the efficacy of a color saturation discrimination test (CSDT) in assessing potential macular function in eyes with cataract. SETTING: Yamanashi Medical University and Nirasaki City Hospital, Yamanashi, Japan. METHODS: In this prospective study of 200 consecutive eyes with cataract, the thresholds of color saturation discrimination on 6 hues were measured with the CSDT. The CSDT program was run on a personal computer and cathode-ray tube color monitor. The preoperative CSDT scores and postoperative visual acuities were compared. In addition, preoperative laser interferometry (LI) and postoperative CSDT were performed on selected patients and the results compared with their preoperative CSDT results. RESULTS: Patients who had a CSDT score of 11 or more had a significantly lower postoperative visual acuity (P < .0001). The prevalence of neuroretinal abnormality postoperatively increased with the preoperative CSDT score. The CSDT score was not correlated with preoperative visual acuity (P = 1409). Cataract severity had little influence on the CSDT score. The preoperative results of the CSDT and Ll were correlated with the postoperative acuity, with the correlation coefficient being stronger with the CSDT (r = -0.338 and 0.276 for CSDT and Ll, respectively). CONCLUSION: The CSDT was effective in evaluating neuroretinal pathology and predicting postoperative acuity.

Cataract↗
PubMedDate not supplied

Critical issues in the use and analysis of the Lanthony Desaturate Color Vision test.

The Lanthony Desaturate Color Vision test (D-15d) has been used to demonstrate the incidence of acquired color vision defects resulting from toxic exposure. The D-15d is a sensitive test designed to grade color deficiencies, but results can be difficult to interpret beyond the qualitative level, and the high incidence of errors reported for controls in some toxicology studies raises questions about how to effectively use this test. This article reviews standard administration of the test, physical determinants of performance, classification of acquired color vision defects, and methods of analysis that have been used to quantify results. The basis for a new method of analysis is discussed, illustrating the source of some characteristic errors, and recommendations are made for test protocols to attempt to more closely identify the type of color vision loss with the goal of identifying the site of toxicological insult.

Color Perception↗
PubMed2000

Sensory and cognitive contributions of color to the recognition of natural scenes.

Although color plays a prominent part in our subjective experience of the visual world, the evolutionary advantage of color vision is still unclear [1] [2], with most current answers pointing towards specialized uses, for example to detect ripe fruit amongst foliage [3] [4] [5] [6]. We investigated whether color has a more general role in visual recognition by looking at the contribution of color to the encoding and retrieval processes involved in pattern recognition [7] [8] [9]. Recognition accuracy was higher for color images of natural scenes than for luminance-matched black and white images, and color information contributed to both components of the recognition process. Initially, color leads to an image-coding advantage at the very early stages of sensory processing, most probably by easing the image-segmentation task. Later, color leads to an advantage in retrieval, presumably as the result of an enhanced image representation in memory due to the additional attribute. Our results ascribe color vision a general role in the processing of visual form, starting at the very earliest stages of analysis: color helps us to recognize things faster and to remember them better.

Cognition↗
PubMed1997

Color appearance depends on the variance of surround colors.

BACKGROUND: The perceived color at each point in a visual scene depends on the relationship between light signals from that point, and light signals from surrounding areas of the scene. In the well known phenomenon of simultaneous color contrast, changing the overall brightness or hue of an object's surround induces a complementary shift in the perceived brightness or hue of the object's color. Color contrast is thought to contribute to color constancy with changes in illumination. RESULTS: We report a new type of simultaneous color contrast, in which changing only the variance (i.e. contrasts and saturations), but not the mean, of colors in a test spot's surround induces a complementary shift in the perceived contrast and saturation of the test spot's color. Objects appear much more vivid and richly colored against low-contrast, gray surrounds than against high-contrast, multicolored surrounds. CONCLUSIONS: Color appearance depends not just on the mean color of the surround, but also on the distribution of surround colors about the mean. This novel form of simultaneous color contrast is inconsistent with a variety of models of color appearance, including those based on sensitivity regulation at the receptor level, and those in which the effects of complex surrounds on color appearance can be reduced to adaptation to the illuminant or induction from a homogeneous 'equivalent surround'. It tends to normalize the gamut of perceived colors in each visual scene and may also contribute to color constancy under viewing conditions that affect contrast.

Color Perception↗
PubMedDate not supplied

Colour vision: Is colour constancy real?

Colour constancy is typically weaker in the laboratory than it seems in our everyday experience. New measurements using real-world stimuli show that colour constancy is in fact almost perfect, and that several different perceptual mechanisms contribute to achieving it.

Color Perception↗
PubMed1987

Colour vision abnormalities in multiple sclerosis.

A battery of colour vision tests was employed to evaluate visual function in patients with multiple sclerosis (M.S.). Colour deficits were found in 45% of patients tested with the Ishihara plates and 42.5% of patients tested with the FM 100-Hue test. 65% of M.S. patients failed at least one of the tests. The colour vision deficits were not restricted to patients with optic neuritis or with visual evoked potential (VEP) abnormalities and there was no significant correlation between an abnormal VEP latency and a colour vision deficit. Colour vision testing may be a useful option to consider in the investigation of M.S. patients, even if there is no other evidence of visual system involvement.

Adult↗
PubMed1989

Color vision in the dog.

The color vision of three domestic dogs was examined in a series of behavioral discrimination experiments. Measurements of increment-threshold spectral sensitivity functions and direct tests of color matching indicate that the dog retina contains two classes of cone photopigment. These two pigments are computed to have spectral peaks of about 429 nm and 555 nm. The results of the color vision tests are all consistent with the conclusion that dogs have dichromatic color vision.

Animals↗
PubMedDate not supplied

High color-vision sensitivity in macaque and humans.

Psychophysical (behavioral) detection thresholds and color-discrimination thresholds were determined in a macaque using a two-alternative forced-choice procedure. On a white background, detection thresholds were determined for a white increment and three spectral increments: 618, 516, and 456 nm. Intermixed with detection threshold determinations, color-discrimination thresholds were determined by presenting the white increment, and one of the spectral increments, at 1.0 log units above their respective detection thresholds and dimming both until discrimination performance fell to threshold. The monkey could discriminate the color of the increments at detection threshold because the average color-discrimination threshold was 0.98+/-0.14 log attenuation. Because the monkey was much more sensitive to the spectral increments than the white increment, we performed an unconventional experiment. We determined the monkey's detection threshold for the white increment alone, and with broadband color filters in the white light path without adjusting the light's intensity. Insertion of several color filters in the light path lowered detection thresholds of both the macaque and six human trichromats. We believe that this improvement in detection thresholds produced by simply inserting color filters in a white light path is a threshold manifestation of the Helmholtz-Kohlrausch effect and suggests that one of color vision's important evolutionary advantages may be improved detection sensitivity.

Adolescent↗
PubMedDate not supplied

Differential distributions of red-green and blue-yellow cone opponency across the visual field.

The color vision of Old World primates and humans uses two cone-opponent systems; one differences the outputs of L and M cones forming a red-green (RG) system, and the other differences S cones with a combination of L and M cones forming a blue-yellow (BY) system. In this paper, we show that in human vision these two systems have a differential distribution across the visual field. Cone contrast sensitivities for sine-wave grating stimuli (smoothly enveloped in space and time) were measured for the two color systems (RG & BY) and the achromatic (Ach) system at a range of eccentricities in the nasal field (0-25 deg). We spatially scaled our stimuli independently for each system (RG, BY, & Ach) in order to activate that system optimally at each eccentricity. This controlled for any differential variations in spatial scale with eccentricity and provided a comparison between the three systems under equivalent conditions. We find that while red-green cone opponency has a steep decline away from the fovea, the loss in blue-yellow cone opponency is more gradual, showing a similar loss to that found for achromatic vision. Thus only red-green opponency, and not blue-yellow opponency, can be considered a foveal specialization of primate vision with an overrepresentation at the fovea. In addition, statistical calculations of the level of chance cone opponency in the two systems indicate that selective S cone connections to postreceptoral neurons are essential to maintain peripheral blue-yellow sensitivity in human vision. In the red-green system, an assumption of cone selectivity is not required to account for losses in peripheral sensitivity. Overall, these results provide behavioral evidence for functionally distinct neuro-architectural origins of the two color systems in human vision, supporting recent physiological results in primates.

Color Perception↗