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At least 1,009 records · Page 56Linked to original sources
PubMed2005

Induction effects for heterochromatic brightness matching, heterochromatic flicker photometry, and minimally distinct border: implications for the neural mechanisms underlying induction.

Brightness induction refers to the finding that the apparent brightness of a stimulus changes when surrounded by a black versus a white stimulus. In the current study, we investigated the effects of black/white surrounding stimuli on settings made between red and green stimuli on three different tasks: heterochromatic brightness matching (HBM), heterochromatic flicker photometry (HFP), and minimally distinct border (MDB). For HBM, subjects varied the relative luminance between the red and green stimuli so that the brightness of the two colors appeared equal. For the two other tasks, matches were made based on minimizing red/green flicker (HFP) or the saliency of a red/green border (MDB). For all three tasks, the presence of black/white surrounding stimuli significantly altered red/green settings, demonstrating the existence of induction effects. These results are discussed in terms of which underlying color pathways (L+ M versus L-M) may contribute to induction effects for the different tasks.

Adaptation, Ocular↗
PubMed2005

Regulation of chromatic induction by neighboring images.

We deal with the regulation of chromatic contrast when the induction of a second stimulus (one of five neighboring surrounds) opposes the induction from a first stimulus (one of two remote vivid peripheral fields). Using a hue cancellation judgment, we show that, although every neighboring surround that we used has the same average chromatic content, the resulting color appearance of the target differs between surrounds, and this may be ascribed to the spatiochromatic organization of the surround. So, rather than the chromatic contrast amplitude or the frequential structure of the surround, it is the structure of proximity that matters.

Adaptation, Ocular↗
PubMed2005

The watercolor illusion and neon color spreading: a unified analysis of new cases and neural mechanisms.

Coloration and figural properties of neon color spreading and the watercolor illusion are studied using phenomenal and psychophysical observations. Coloration properties of both effects can be reduced to a common limiting condition, a nearby color transition called the two-dot limiting case, which clarifies their perceptual similarities and dissimilarities. The results are explained by the FACADE neural model of biological vision. The model proposes how local properties of color transitions activate spatial competition among nearby perceptual boundaries, with boundaries of lower-contrast edges weakened by competition more than boundaries of higher-contrast edges. This asymmetry induces spreading of more color across these boundaries than conversely. The model also predicts how depth and figure-ground effects are generated in these illusions.

Adaptation, Ocular↗
PubMed1986

Accuracy of memory for brightness of colored lights measured with successive comparison method.

Successive and simultaneous brightness comparisons between test colors and a comparison white were performed to study how accurately the brightness of colored lights was maintained in memory. The test colors were monochromatic lights chosen from 410 to 670 nm and a white light. The stimulus duration was 1 sec, and test-comparison stimulus-onset asynchronies in successive comparisons were more than 11 sec depending on the experiments. The results show that the variability of successive brightness comparisons was 1.5-2.0 times greater than that of simultaneous brightness comparison. This degree of deterioration of brightness discrimination is reasonably consistent with those of hue and saturation discrimination previously reported. Brightness shifts in the darker direction were found for most colors.

Color Perception↗
PubMed1986

Psychophysics of reading. IV. Wavelength effects in normal and low vision.

Does the color of text influence its legibility? There are reasons why it may do so for specific groups of low-vision observers. We used psychophysical methods to measure the effects of wavelength on the reading performance of four normal observers, two dichromats, and twenty-five low-vision observers. Reading rates were measured for text scanned across the face of a television (TV) monitor. We compared performance under four luminance-matched conditions in which sets of neutral-density and Wratten color filters were placed in front of the TV screen--blue (lambda max = 430 nm), green (lambda max = 550 nm), red (lambda max = 650 nm), and gray. Under photopic conditions, the reading rates of normal subjects were independent of wavelength, with the exception of characters near the acuity limit. At lower luminances, wavelength effects could be explained by the shift from photopic to scotopic vision. It was hypothesized that light scatter or absorption in eyes with cloudy ocular media would result in depressed performance in the blue. Only one of seven subjects demonstrated this effect, which we traced to wavelength-specific absorption. Observers with advanced photoreceptor disorders tended to read blue text faster than red text. This could not be explained on the basis of photopic spectral sensitivities alone. Finally, the presence of central or peripheral field loss was not predictive of wavelength-specific effects in reading. On the whole, wavelength only occasionally plays a significant role in reading. When it does, performance tends to be depressed either in the red or the blue and to be nearly optimal for green or gray.

Adult↗
PubMed1988

Factors underlying individual differences in the color matches of normal observers.

We have used a factor analysis of the Stiles-Burch [Opt. Acta 6, 1 (1959)] 10 degrees field color matches to examine the basis of individual differences in the color matches made by observers with normal color vision. The differences in the matches are primarily due to interobserver variations in the macular-pigment density [with a standard deviation (sigma) of 0.12 at 460 nm]; the lens-pigment density (sigma = 0.18 at 400 nm); the spectral position of the long-wavelength-sensitive (sigma = 50.3 cm-1), medium-wavelength sensitive (sigma = 31.9 cm-1), and short-wavelength-sensitive (sigma = 45.3 cm-1) photopigments; the covarying densities of the three photopigments (sigma = 0.045); and the degree of rod intrusion. Variations in the different factors appear to be uncorrelated. Comparable estimates of the sources and range of interobserver differences in color matching were obtained from a similar analysis of the Stiles-Burch 2 degrees color matches [Opt. Acta 2, 168 (1955)].

Color Perception↗
PubMed1988

Direct psychophysical estimates of the cone-pigment absorption spectra.

The absorption spectra of the long- and medium-wavelength-sensitive cone photopigments were derived by determining the spectra that best accounted for either the individual differences in the Stiles-Burch 10 degrees color matches [Opt. Acta 6, 1 (1959)] or the changes in color matches at high light levels due to photopigment bleaching [Vision Res. 20, 23 (1980)]. The estimates were made by finding the best-fitting coefficients for an 11th-order polynomial function of wavelength, with no requirement that the resulting sensitivities be consistent with the color-matching functions. The estimates are independent of the scaling effects of any inert screening filters and therefore directly reflect the photopigment sensitivities. The spectra implied by the differences in the matches are similar to the absorption spectra of Smith et al. [Vision Res. 16, 1087 (1976)], which were used as initial estimates. However, the peak sensitivity of the required long-wavelength-sensitive pigment is shifted toward slightly longer wavelengths.

Color Perception↗
PubMed1988

Quantitative studies of color constancy.

In order to study color constancy, the color appearance of the center of a center-surround paradigm was measured by using multiple-alternative forced-response matching. The center was presented with (1) no surround, (2) an adjacent chromatic surround, or (3) a chromatic surround separated from the center by an achromatic gap. The center and the surrounds were presented under various simulated illuminants ranging from illuminant A to illuminant D75. We found that when no surround is present, color constancy fails; however, when surrounds are present, some degree of color constancy is displayed. We also found that color constancy is poor when chromatic induction is minimal. In addition, it was determined that, if the ratios of R, G, and B of the center to R, G, and B of the surround remain constant as the illuminant changes, color constancy results. (R, G, and B correspond to the outputs of the retinal color mechanisms).

Color↗
PubMed1990

Wavelength discrimination at detection threshold.

The experiments that we report aim to elucidate the linkage between cone outputs and color sensation. This is investigated by measuring wavelength discrimination between stimuli at threshold levels of detection. Stimuli are large spots (0.75 deg) presented on a white background. A 2 x 2 alternate forced choice method is used to measure simultaneously the detection of different wavelengths and discrimination between them. This method reveals at least four distinguishable colors, indicating the presence of four different sets of mechanisms at threshold. These are associated with the color sensations of orange, pale yellow, green, and blue. There is also evidence for a fifth imperfectly distinguished color (violet) in the shortest wavelength region. Results show that the boundaries between the distinguishable colors have little variation in their spectral positions. This is compatible with the presence of fixed perceptual boundaries in the spectrum dividing the different types of detection mechanism. The correspondence of the spectral locations of the distinguishable colors to the cone opponent responses revealed in the spectral sensitivity function suggests that these color sensations are postreceptoral in origin, arising from different combinations of the three cone outputs.

Calibration↗
PubMed1990

Task-dependent color discrimination.

When an observer's ability to discriminate colored objects is estimated from the variability in color matches, the observer inspects adjacent visual fields carefully and makes considered judgments. Color discrimination does not always take place under such viewing conditions. When color video displays are used in time-critical applications (e.g., head-up displays, video control panels), the observer must discriminate among briefly presented targets seen within a complex spatial scene. We compare color-discrimination thresholds by using two tasks. In one task the observer makes color matches between two halves of a continuously displayed bipartite field. In a second task the observer detects a color target in a set of briefly presented objects. The data from both tasks are well summarized by ellipsoidal isosensitivity contours. The fitted ellipsoids differ both in their size, which indicates an absolute sensitivity difference, and orientation, which indicates a relative sensitivity difference.

Calibration↗
PubMed1991

Large color differences and selective attention.

Similarity data for large color differences, obtained with triadic comparisons, are presented. Approximately 63,000 judgments are collected. We have compared the performance of the CIELUV, the CIELAB, and the Optical Society of America's [symbol; see text] jg color spaces, using three different color sets and two instructions. For color sets containing large color differences in the isoluminant plane, the [symbol; see text] jg color space outperforms the CIELUV and CIELAB spaces. We also investigated the effects of selective attention and conclude that, for judgments of large color differences, selective attention leads to significant changes in the relative contribution of the brightness dimension on the one hand and the hue and saturation dimensions on the other hand.

Adult↗
PubMed1997

Electrophysiological measurements of spectral sensitivities: a review.

Spectral sensitivities of visual systems are specified as the reciprocals of the intensities of light (quantum fluxes) needed at each wavelength to elicit the same criterion amplitude of responses. The review primarily considers the methods that have been developed for electrophysiological determinations of criterion amplitudes of slow-wave responses from single retinal cells. Traditional flash methods can require tedious dark adaptations and may yield erroneous spectral sensitivity curves which are not seen in such modifications as ramp methods. Linear response methods involve interferometry, while constant response methods involve manual or automatic adjustments of continuous illumination to keep response amplitudes constant during spectral scans. In DC or AC computerized constant response methods, feedback to determine intensities at each wavelength is derived from the response amplitudes themselves. Although all but traditional flash methods have greater or lesser abilities to provide on-line determinations of spectral sensitivities, computerized constant response methods are the most satisfactory due to flexibility, speed and maintenance of a constant adaptation level.

Color Perception↗
PubMed2005

A study of hue identification in the hue circle of the HSB color space.

The purpose of the present research was to explore the relationship between the sensory difference in hues in the hue circle of the HSB color space and their included angles in identification tasks. In the experiment, the two colors were presented separately, and the test subjects judged whether the two colors were the same or different. Five hues, called Standard Stimulus Hues and the most saturated colors in the hue circle of the HSB color space, were discussed. These are hue 0 degrees, hue 72 degrees, hue 216 degrees, and hue 288 degrees in the HSB color space. The Just Identifiable Angle refers to the included angle between a specific standard hue and the hue which cannot be identified separately and which is the furthest from the standard hue in the hue circle of the HSB color space. Analysis gave a significant main effect of standard hue. The Just Identifiable Angles for hue 72 degrees and hue 288 degrees did not differ significantly, but their Just Identifiable Angles were discernibly lower than those for the other three hues. The Just Identifiable Angle of hue 144 degrees was significantly lower than those for hue 0 degrees and hue 216 degrees. In addition, the Just Identifiable Angle for hue 0 degrees was noticeably larger than the one for hue 216 degrees, so the final outcome might show that the Just Identifiable angles of the standard hues are not equal.

Adolescent↗
PubMed1991

Methodological consideration in color research.

Color can influence physical and emotional variables, but the evidence is equivocal. Replications are often hampered by inadequate specification of colored stimuli. It is proposed that a standardized method for reporting colored stimuli should be employed to facilitate empirical testing of the effects of color, namely, the CIE chromaticity coordinates x and y or Munsell values, for both allow translation from one to the other.

Color↗
PubMed1991

Oral contraceptive use, caffeine consumption, field-dependence, and the discrimination of colors.

We attempted to validate laboratory research which indicated that single doses of oral contraceptives (OCs) and caffeine affect the ability to discriminate colors (Böhme & Böhme, 1985). We did this in a nonlaboratory setting by surveying habitual use of OCs and caffeine by 43 female college students and relating that information to their performance on the Farnsworth-Munsell 100-Hue Test. When field-dependence, conceptualized as an indirect measure of sensitivity of the nervous system and previously shown to be strongly related to color discrimination, was included in the analyses, the results supported Böhme and Böhme's findings. For Trays 2 and 3 of the 100-Hue Test (yellow through blue of the color spectrum), higher caffeine consumption among OC users was related to poorer color discrimination, whereas, among nonusers of OCs, it was related to better performance. Study design limitations do not permit attribution of causation to either caffeine or OCs at this time.

Adolescent↗
PubMed1993

Priming effect in a color discrimination task.

Two experiments were run to test whether the automatic coding of colors generates priming effects. Subjects were tachistoscopically presented a series of prime-target sequences. The prime stimulus could be either a red, green, or black circular dot, followed by a red or green annular ring (target). The role of automatic and conscious mechanisms was investigated in Exp. 1 by manipulating the predictive validity of the prime stimuli (80%, 50%, 20%), keeping constant the value of stimulus-onset asynchrony (350 msec.). Analysis showed priming effects even in the low predictive condition, where no conscious expectations could be activated. In Exp. 2, three different values of stimulus-onset asynchrony were used, 150, 350, and 2100 msec. Priming effects were obtained in the short and medium stimulus-onset asynchrony condition but not in the long one. Over-all, the data of both experiments produce converging evidence which indicates that the automatic elaboration of colored stimuli may produce priming effects.

Adult↗