Purity Discrimination Research Articles

ディスプレイ―ＩＤＷ’１０を中心に―薄明視条件下における単色光と混色光に対応する純度弁別

The purity discrimination threshold of monochromatic light and mixed light was investigated in the mesopic condition. Monochromatic light and mixed light were first resolved into their components of pure color light of dominant wavelength and white light. By Using the definition of colorimetric purity, the luminance ratios of the pure color light to white light were obtained. The pure color light component in mixed light was calculated Using the luminance ratios. The purity discrimination threshold of monochromatic and mixed light is expressed by the ratio of the pure color component to the white light of a reference field. Therefore, this purity discrimination threshold can be expressed in a unified manner.

Color discrimination in heterozygous deutan carriers.

The color discrimination abilities of heterozygous deutan female carriers were measured using color mixture thresholds and compared with those of suspected nonheterozygous normal subjects. Eight test subjects and 26 control subjects were run on a computer-controlled color test (color mixture thresholds) that presented 1 degree diameter spots on a color television monitor for 1/60 of a second. A QUEST procedure was used to determine visual thresholds for spots varying in brightness and/or color. Individual data points were graphed on an X/Y plot and fitted with an ellipse. The major and minor diameters of the ellipse represent the color and brightness thresholds, respectively. The mean axis angle of the ellipse for the heterozygous carriers did not differ from that for the controls (15.75 degrees vs. 14.93 degrees, p = 0.428, Mann-Whitney test). The carriers did show, however, a larger mean major axis length (68.79 vs. 46.78, p = 0.0218, Mann-Whitney test). Additionally, the length-to-width ratios for the carriers were higher than the controls (9.34 vs. 6.80, p = 0.0403, Mann-Whitney test). Deutan-carriers do show reduced color purity discrimination as measured using color mixture thresholds compared with nonheterozygous, color vision normals.

Aging and the saturation of colors. 1. Colorimetric purity discrimination.

Colorimetric purity (Pc) discrimination functions were measured for 21 color-normal observers (11 younger and 10 older observers with mean ages of 30 and 74 years, respectively). On each two-alternative-forced-choice trial, observers saw two flashes of light, a broadband white light [CIE(x, y) = (0.33, 0.35)] and a mixture of broadband and monochromatic light (420-680 nm). The observer's task was to choose the flash that had a chromatic component. Foveally viewed, circular, 1.2 degrees-diameter stimuli were presented as 1.5-s flashes with 3-s interstimulus intervals in Maxwellian view. Stimuli [250 trolands (td) and 10 td] were equated on the basis of individual heterochromatic flicker photometry functions. Measured Pc discrimination sensitivity was lower in the older group than in the younger group at both light levels, and the performance difference between the age groups was approximately constant across the spectrum. The difference between discrimination at 10 and 250 td was relatively small for the younger group but larger for the older group, indicating a selective performance decrement for older observers at low light levels. The data were modeled as a sum of differential responses from S-cone and L/M-cone chromatic channels. The model and the data indicate similar age-related losses of sensitivity in the two channels, perhaps secondary to receptorial sensitivity losses.

Increment threshold and purity discrimination spectral sensitivities of X-chromosome-linked color-defective observers

The goal of the study was to evaluate spectral opponency in nine X-chromosome-linked color-defective observers. The tasks included increment threshold spectral sensitivity on an achromatic background, heterochromatic flicker photometry, and colorimetric purity discrimination. With a task of heterochromatic flicker photometry, the anomalous trichromatic observers showed spectral sensitivity of the corresponding dichromat. The increment threshold spectral sensitivity and colorimetric purity discrimination data were analyzed using the concept of standard cone photopigment spectral sensitivities for normal and defective vision, and a model that postulates one cone-additive and two cone-antagonistic systems. The model incorporated a shift of the peak spectral sensitivity of the long-wavelength-sensitive (LWS) pigment (for protan observers) or of the middle-wavelength-sensitive (MWS) pigment (for deutan observers). Two dichromats and two anomalous trichromats did not show clear evidence of LWS vs MWS cone antagonism. Five anomalous trichromats showed such cone antagonism. Molecular genetic analysis of the opsin genes is presented for eight of the observers.

Helmholtz-Kohlrausch効果, 測色純度弁別, およびG0関数について

Helmholtz-Kohlrausch効果, 測色純度弁別, およびG<SUB>0</SUB>関数について

Colorimetric purity discrimination: Data and theory

Colorimetric purity, measured as the first step from white toward the spectrum has a V-shaped function. Purity discrimination is best near 400 nm, least at 570 nm and intermediate at mid-spectrum and long wavelengths. A much flatter function occurs when Colorimetric purity is measured as the first step from the spectrum toward white. In this study, we applied the formulation of chromatic discrimination thresholds measured along the S-cone and M/L-cone axis to account for chromatic discrimination in the equiluminant plane. The modeling results show that the purity step from white has a 1.6 log unit calculated range, similar to the classical data. The purity step from the spectrum is much flatter. The predicted range is dependent on the individual variance in chromatic discrimination thresholds and the luminance level. We then used psychophysical procedures to test the model's predictions. The resulting purity discrimination functions were generally in agreement with the model. Our modeling indicates that discrepant data of Colorimetric purity can be explained with the context of discrimination models.

Relation between Helmholtz-Kohlrausch Effect, Purity Discrimination, and Go Function.

Using the nonlinear color-appearance model, predicted are the four kinds of color-perception phenomena, which are the Go function studied by Evans, Munsell Values for different hues, purity discrimination, and the Helmholtz-Kohlrausch effect. The analysis confirmed that all the four phenomena are caused by the same common factor, the chromatic strength of spectral color stimulus reported by Evans in 1967.

Color vision in the ring-tailed lemur (Lemur catta).

Behavioral discrimination tests were used to examine spectral sensitivity and color vision in a pair of ring-tailed lemurs (Lemur catta). Sensitivity tests revealed the presence of a Purkinje shift and a photopic visual system. As measured at increment-threshold, the photopic spectral sensitivity function for the lemur has multiple peaks (at ca. 440-460, 540, and 620 nm). In color vision tests lemurs behave trichromatically in that (a) they show no evidence for a neutral point in the spectral range of 470-510 nm, and (b) they set a unique Rayleigh match (540 nm + 645 nm = 570 nm). Tests of wavelength and colorimetric purity discrimination reveal that although this prosimian has color vision, it is not an acute capacity--thresholds for these color discriminations were consistently much higher for lemurs than for normal human trichromats tested in the same situation.

Purity discrimination: Successive vs simultaneous comparison method

Purity discrimination thresholds ( Δp) were measured with successive (SOA = 3 sec) and simultaneous (SOA = 0 sec) comparison methods for seven dominant wavelengths: 410, 480, 500, 530, 570, 600 and 650 nm. The stimulus duration was 1 sec. The Δp values with the successive comparison method were found to he about 1.5–2.0 times larger than those obtained in the simultaneous case. The degree of purity discrimination deterioration shown in this study is similar to that of wavelength discrimination deterioration previously reported ( Uchikawa and Ikeda, 1981, Vision Res. 21, 591–595). Saturation shifts of stimuli with the successive comparison method were also observed: these were toward increased saturation direction for most dominant wavelengths.

Single cell analysis of saturation discrimination in the macaque

Responses of 53 cells to stimuli varying in purity were recorded from the macaque LGN. The type of response (either excitation or inhibition) of any given cell was determined by the stimulus wavelength while the response magnitude was determined by stimulus purity. Pure stimuli (highly saturated) resulted in large response magnitudes, whether excitation or inhibition. The purity increment required to change the response rate of a unit by an arbitrary response criterion was determined for all cells. The reciprocal of the purity increment plotted against wavelength yielded a purity discrimination function in good agreement with that obtained behaviorally from macaque monkeys.