The effects of psychophysical procedure and stimulus duration in the measurement of Bezold-Brücke hue shifts.
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Color Perception↗
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Induced desensitization.
Viewing of annuli modulated in color in a sawtooth fashion in time results in differential threshold elevations for the detection of color changes of inscribed disks. The elevations are of nearly the same magnitude as those resulting from viewing modulated disks. However, the differential effects on thresholds for complimentary colors are reversed. The differential effects, thus, are correlated with the variation in appearance of the test area.
Color Perception↗
Additivity of yellow chromatic valence.
The additivity of yellow chromatic valence was investigated by the hue cancellation method for two normal observers. Additivity held in 530-550 nm and 600-630 nm pairs, while additivity failure of reduction type occurred in 530-570 nm pair for both observers. Additivity failure of enhancement type occurred in 530-600 and 530-630 nm pairs in which one observer showed reduction type failure when mixture ratio of 530 nm is greater than 600 or 630 nm. The results suggest a nonlinear property of the yellow-blue process and are discussed in an interaction between the two opponent processes.
Color Perception↗
A comparative study of successive and simultaneous methods in colour discrimination.
Simultaneous and successive methods of comparison of stimuli are studied by comparing experimental results of colour discrimination experiments. In this way, colour differential thresholds for two normal observers and four different stimuli were measured by the two methods. In most cases, the capacity to discriminate colour decreased when the successive method was used, although no differences were found in qualitative aspects of discrimination. These results differ somewhat from previous reports in this field, probably because of experimental differences in the method of obtaining the thresholds.
Color Perception↗
Temporal induction of blackness--I. Color appearance.
Three color-normal observers described the appearance of colors under conditions of temporal induction. One of four inducing fields (unique blue, unique green, unique yellow, unique white) was foveally viewed for 5 sec followed immediately by a 400 msec reference stimulus of the same size (0.75 deg) and spatial location as the inducing field. The reference stimulus was 3 or 5 td and appeared achromatic to the observer when viewed without the inducing field. After presentation of this temporal sequence, the observers described the reference stimulus by assigning percentages to the terms red, green, yellow, blue, white and black. The range of inducing field intensities was -0.4-3.2 log td. Both chromatic and achromatic induction occurred at low illuminance levels of the inducing fields. As the illuminance of the inducing field increased, the reference stimulus gradually became blacker and the chromatic components less prominent. The minimum illuminance level at which the reference appeared 100% black was the same for the four different inducing fields.
Adult↗
Do deviations from radiance-invariance of metameric matches contradict the three pigment theory of foveal trichromacy?
According to the pigment theory of matching, metameric matches result from the equation of the rates of photoisomerizations for each of the three classes of cone pigments excited by the two matched fields. If true, matches are radiance-invariant and additive. Tests of the theory in this paper show small but ubiquitous failures in radiance-invariance due to systematic rather than random errors in matching. A choice between two possible explanations for these systematic errors favors the view that in subjects who deliberately or intuitively search for the middle of the matching range, the errors are due to an asymmetry in the Weber fraction for color (Trezona) at low (but not high) levels of retinal illuminance.
Analysis of Variance↗
Foveal cone detection statistics in color-normals and dichromats.
We measured for six male observers, the psychometric functions for the detection of two simultaneously presented points of light. The test stimuli were two 1 min point sources separated by 17 min arc, and pulsed for 0.5 msec. The stimuli varied in wavelength from 500 to 620 nm. The psychometric functions were fit with a model that assumes ideal detection and the following properties: (1) Poisson-distributed quantal absorptions; (2) binomial sampling of foveal long-wavelength-sensitive (LWS) and middle-wavelength-sensitive (MWS) cones; (3) independent responses of the LWS and MWS cones; and (4) the Smith-Pokorny fundamentals for cone spectral sensitivities. Based on chi 2 fits to the psychometric functions for detecting neither, one or both of the two-point stimuli presented, estimates were derived for the minimum quantal catch by a single cone for detection (C), the number of effective cones illuminated by a point stimulus at threshold (N) and the proportion of central foveal cones of the LWS type (PL). Three observers were color-normal, two were protanopes and one was a deuteranope. A second deuteranope was included in the design but his data were too unreliable for an unambiguous solution. The estimated quantal requirement C was consistently near 5(4-6), and the effective number of illuminated cones always was 1 or 2. The plausible range of PL (98% confidence interval) for the color-normal observers was 0.48-0.68 (observer YY), 0.76-0.90 (observer MW) and 0.77-0.95 (observer DF). The best fitting PL solution for these observers were 0.61, 0.82 and 0.88, respectively. These were comparable to the values obtained from flicker photometric data. The best PL value for each of the protanopes was 0.00 and for the deuteranope the best PL value was 0.98.
Color Perception↗
Changes in pattern induced flicker colors are mediated by the blue-yellow opponent process.
The colors of Benham's Top [pattern induced flicker colors (PIFCs)] were matched with color stimuli provided by a computer aided color mixer. Subjects viewed a series of specifically modified black and white disks and matched the resulting subjective color with a comparison field containing the color generated by additive mixing. Different phase relations between the apparently colored ring and the surround were tested. The color loci of all PIFCs were found to lie on a plane in receptor three-space which is given by the axis of the shortwave receptor excitation and a vector given by combining the middle and long wave receptor excitation directions in a fixed ratio of nearly 1:1. From the orientation of this plane it can be deduced that the blue-yellow opponent process (the blue-on-center cells) alone accounts for the different PIFCs.
Adult↗
Color discrimination and adaptation.
We have measured color discrimination in the isoluminant plane under rigorously controlled adaptation conditions. Two regimes were studied. Under the first regime the observer was adapted to the region of color space in which the discriminations were made. Thresholds for detecting changes along the S-(L + M) axis are a linearly increasing function of the excitation of the S cones. Thresholds for detecting changes along the L-M axis are independent of the locus of adaptation along this axis. The straightness of these functions is inconsistent with the theory that second stage mechanisms are more sensitive in the middle of their operating ranges. No convincing evidence of interactions in the effects of adaptation locus or test stimuli was observed. Under the second regime the observer was adapted to one point in color space and the stimuli to be discriminated were located in other places in color space. Discrimination seems to be limited primarily by mechanisms maximally sensitive to modulation along the isoluminant cardinal axes but evidence suggestive of the operation of higher order mechanisms was also found.
Adaptation, Ocular↗
Reversal in the sequence of the Benham colours with a change in the wavelength of illumination.
A Benham disk was rotated at 7 c/sec and illuminated by monochromatic lights from the range 534-586 nm. The elicited colours of the rings were described either with a colour naming procedure or by matching with a Munsell chip. Exchanges of hues between the two extreme rings and between the two inner rings were reported around 557 and 566 nm by the colour naming procedure, thus resulting in a hue reversal in the spatial display of colours. Similar hue shifts were also reported with the matching procedure. The effect of a possible displacement in the equilibrium of colour-opponent cell population, resulting from chromatic adaptation, is discussed.
Adaptation, Ocular↗
Methodology-specific Rayleigh-match distributions.
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Adolescent↗
Systematic measurement of human neonatal color vision.
We used a new time-efficient method to evaluate chromatic-achromatic discrimination in newborn (n = 36) and 1-month-old (n = 34) human infants. Results showed that 74% of newborns discriminated a 10.5 x 17.5 deg broadband red patch from all relative luminances of an achromatic background, but only 14% of newborns did so with a blue, 36% with a green, and 25% with a yellow patch. Most infants who "failed" did so at relative luminances very close to the respective photopic luminance match. At 1 month, performance improved somewhat although infants still show clear evidence of discriminating only the red patch. These results, the first to be obtained from individual newborns with a method incorporating a systematic variation of luminance, imply that early color vision is very limited. Possible photoreceptoral and neural bases for these immaturities are discussed.
Child Development↗
A double-blind placebo-controlled evaluation of the acute effects of sildenafil citrate (Viagra) on visual function in subjects with early-stage age-related macular degeneration.
PURPOSE: To assess the effects of a single 100-mg dose of sildenafil citrate on visual function in men with early-stage age-related macular degeneration. DESIGN: Randomized double-blind placebo-controlled clinical trial. METHODS: Nine men (mean age 71 years, range 59-85 years) with early-stage (minimal visual impairment and large drusen in the macula) age-related macular degeneration and 20/40 or better-corrected visual acuity in at least one eye were prospectively randomized to receive either placebo or sildenafil citrate (Viagra; Pfizer Inc, New York, New York) 100 mg as a single oral dose. After 7-14 days, they received the alternate treatment. Subjects underwent visual acuity, Amsler grid, color discrimination (D15), traffic light, Humphrey perimetry, and photo-stress testing in each eye before and at specific intervals within 8 hours after dosing. RESULTS: Compared with placebo, no pattern of errors were evident in any visual function test following sildenafil administration. No statistically or clinically relevant changes from baseline were observed in visual acuity, Humphrey perimetry (corrected pattern standard deviation), D15 color discrimination, or photo-stress tests. No clinically relevant changes were observed in the Amsler grid or traffic light tests. Sildenafil treatment was associated with transient mild or moderate headache, flushing, and rhinitis. There were no visual adverse events spontaneously reported to the investigator. CONCLUSION: A single 100-mg dose of sildenafil was well tolerated and produced no acute visual effects or exacerbation of preexisting visual impairment in nine men with early-stage age-related macular degeneration.
3',5'-Cyclic-GMP Phosphodiesterases↗
Acquired color vision defects in retrobulbar neuritis.
We used the Farnsworth-Munsell 100 Hue Test to study the incidence of acquired color vision defects in 16 patients with unilateral and and seven patients with bilateral retrobulbar optic neuritis whose visual acuity had recovered to 6/12 (20/40) or better. We recorded the visual-evoked response to a pattern stimulus on the same day. All 30 affected eyes showed an excessive number of errors on Farnsworth-Munsell 100 Hue testing. The number of errors increased with greater residual optic nerve damage. One false-positive and two false-negative visual-evoked responses were found.
Adult↗
Ishihara color plates as a test for simultanagnosia.
PURPOSE: To alert ophthalmologists to the use of Ishihara color plates in the detection of simultanagnosia. METHODS: We examined seven patients referred for impaired vision. Evaluation included color plate testing with Ishihara color plates. RESULTS: All seven patients had simultanagnosia, with marked difficulty in identifying the numbers in Ishihara color plates despite adequate visual acuity and the ability to name all of the colors in the plates correctly. One of these patients was referred with the diagnosis of a cone dystrophy because of her poor performance on the Ishihara test. All of the patients had bilateral occipitoparietal damage or atrophy on magnetic resonance imaging. CONCLUSIONS: Ophthalmologists must be aware that a poor performance with Ishihara plates may not be attributable to an impairment of color vision but rather to occipitoparietal brain damage associated with simultanagnosia.
Agnosia↗
Applications of glass filters in gastrofiberscopy.
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Color Perception↗
Psychophysical tests in X-linked retinitis pigmentosa carrier status.
Psychophysical tests were performed in 22 normal women and 17 X-linked carriers of retinitis pigmentosa. The tests consisted of luminance contrast sensitivity, grating at the fovea and broken annulus at the periphery, color contrast sensitivity, letters for the fovea and broken annulus for the periphery, along the three known confusion axes of protan, deutan and tritan observers. Statistical analysis of the data shows that there were significant differences between the carriers and age-similar normal subjects with all the tests. The most significant differences (P < 0.001) were found with the color contrast sensitivity at the periphery along the protanopic and deutanopic axes and the luminance contrast sensitivity at the periphery. The influence of the age is discussed.
Adolescent↗
Chromatic induction and the layout of colours within a complex scene.
A target's apparent colour is influenced by the colours in its surrounding. If the surrounding consists of a single coloured surface, the influence is a shift 'away' from the surface's colour. If the surface is more than 1 degrees from the target area the shift is very small. If there are many surfaces, then not only the average luminance and chromaticity of the surfaces matters, but also the chromatic variability. It is not yet clear whether it makes any difference where the chromatic variability is within the scene, so we constructed stimuli in which the chromatic variability was restricted to certain regions. We found that it made very little difference where the chromatic variability was located. The extent to which the average colour of nearby surfaces influences the apparent colour of the target seems to depend on the average chromatic variability of the whole scene.
Color Perception↗