Chromatic Discrimination Research Articles

Luminance and chromaticity discrimination sensitivities right after an abrupt decrease in background luminance

AbstractWhen we enter a dark place, such as a tunnel, from a bright exterior, our visual sensitivities take some time to adapt to lower light levels. However, there have been few reports on how quickly luminance and chromaticity discrimination sensitivities recover in this situation. This study aims to quantify the time course of discrimination sensitivity for luminance and chromaticity directions after an abrupt decrease in background luminance. In each trial, the background luminance was decreased from 100 to 1 cd/m2. Subsequently, one target and three reference stimuli of different colors were presented under four stimulus‐onset asynchrony (SOA) conditions. The participants discriminated the target stimulus from reference stimuli. The results showed that discrimination sensitivity was the lowest right after the background luminance changed and gradually improved with SOAs. The sensitivity decreases differed across color directions, with the greatest decrease in luminance, a moderate decrease in S−(L + M), and a negligible change in L−M. However, statistically significant differences were observed only between luminance and L−M, suggesting that the sensitivity decrease after the abrupt decrease in background luminance did not significantly differ between the chromaticity directions. We speculate that these results stem from the interaction between chromatic perception and luminance adaptation, and possibly from rod intrusions.

Color discrimination in fixed saturation level of patients with acute traumatic injury.

Traumatic brain injury (TBI) is an important public health concern and that may lead to severe neural sequels, such as color vision deficits. We evaluated the color vision of 10 TBI patients with normal cognitive function using a color discrimination test in a fixed saturation level. We also analyzed computerized tomography scans to identify the local of the brain damages. Four TBI patients that had lesions in brain areas of the ventral visual streams, five TBI patients had lesions inferred in brain areas of the dorsal visual stream, and one TBI patient had lesion in the occipital area. All the patients had cognitive and color vision screened and they had characterized the chromatic discrimination at high and low saturation. All participants had no significant cognitive impairment in the moment of the color vision test. Additionally, they had perfect performance for discrimination of chromatic stimulus at high saturation and similar to controls (n = 37 age-matched participants). Three of four TBI patients with lesions in the ventral brain and one patient with lesion in the occipital area had impairment of the chromatic discrimination at low saturation. All TBI patients with lesions in the dorsal brain had performance similar or slightly worse than the controls. Chromatic discrimination at low saturation was associated to visual damage in the ventral region of the brain and is a potential tool for functional evaluation of brain damage in TBI patients.

A colour vision test assisted by neural networks

Aims/Purpose: Traditional computerized colour vision tests resort to the magnitude of chromatic thresholds to determine the quality of the colour vision of an observer. The limits of perceived colours are tested against a background that will be conspicuous to normal colour vision observers, but inconspicuous to colour vision deficient (CVD) observers. The purpose of this work was to implement a Neural Network capable of performing independent and automatic classification of the colour vision of an observer, using as inputs the sRGB chromaticity coordinates, response times, and eye movements obtained using a colour vision test on a computer screen calibrated in colour and luminance (Display++).Methods: Chromatic discrimination limits were estimated using a staircase procedure that tested colour vision close to the dichromatic confusion lines. Only the last 8 responses were considered in the analysis. 50 normal colour vision observers and 8 CVD observers performed the test on Display++. CVD participants were diagnosed using the results of the anomaloscope and the CAD colour vision tests. A Sequential Neural Network was implemented with a dense structure (256–128–64‐16‐1 nodes), with relu and sigmoid activation functions, dropout commands to prevent overfitting, the Adam optimizer, and the binary crossentropy loss function. The performance of the neural network was estimated by computing its accuracy, where variables are related to the results obtained after training the Neural Network and inspecting the test results. The database was divided into a training/test following different splitting strategies: T1 observers' responses considering sRGB coordinates, response times, and eye movements. T2 observers' responses considering only sRGB coordinates.Results: The averages and standard deviations of the estimated accuracy for five consecutive trials with a random division between training/test for conditions T1 and T2 was 91% ± 7% and 93% ± 5% respectively. It was found that the implemented neural network had an accuracy of more than 90% across all conditions.Conclusions: The accuracies found across conditions considered seem to indicate that the implemented Neural Network can analyse and classify the colour vision of human observers, with an accuracy greater than 90% of success.

Poster Session II: Luminance and chromaticity discrimination sensitivities following a sudden decrease in background luminance.

When we enter a dark place like a tunnel from a bright exterior, our visual sensitivities take some time to adapt to the lower light level. However, there have been few reports about how quickly our sensitivities of luminance and chromaticity discrimination recover in this situation. This study aimed to quantify the time course of discrimination sensitivity for luminance and chromaticity directions after an abrupt decrease in background luminance. In each trial, the background luminance dropped from 100 cd/m² to 1 cd/m². Then, one target and three reference stimuli with different colors were presented under four stimulus onset asynchrony (SOA) conditions. The observer was asked to discriminate the target stimulus from the reference stimuli. The results showed that discrimination sensitivity was lowest right after the background luminance change and gradually improved with SOAs. However, sensitivity recovery differed across color directions, with the most improvement in luminance, followed by S, and negligible change in L-M. There was a statistically significant difference between +S and ±(L-M) sensitivities, indicating that the sensitivity recovery after the sudden background luminance change differed between chromaticity directions. Based on the comparison with previous studies, we speculate that both adaptation and masking may contribute to the temporal change of discrimination sensitivities.

Colour perception develops throughout childhood with increased risk of deficiencies in children born prematurely.

To quantify the impact of prematurity on chromatic discrimination throughout childhood, from 2 to 15 years of age. We recruited two cohorts of children, as part of the TrackAI Project, an international project with seven different study sites: a control group of full-term children with normal visual development and a group of children born prematurely. All children underwent a complete ophthalmological exam and an assessment of colour discrimination along the three colour axes: deutan, protan and trytan using a DIVE device with eye tracking technology. We enrolled a total of 1872 children (928 females and 944 males) with a mean age of 6.64 years. Out of them, 374 were children born prematurely and 1498 were full-term controls. Using data from all the children born at term, reference normative curves were plotted for colour discrimination in every colour axis. Pre-term children presented worse colour discrimination than full-term in the three colour axes (p < 0.001). Even after removing from the comparison, all pre-term children with any visual disorder colour discrimination outcomes remained significantly worse than those from full-term children. While colour perception develops throughout the first years of life, children born pre-term face an increased risk for colour vision deficiencies.

Chromatic discrimination in fixed saturation levels from tufted capuchin monkeys with different color vision genotypes.

Recent research has proposed new approaches to investigate color vision in Old World Monkeys by measuring suprathreshold chromatic discrimination. In this study, we aimed to extend this approach to New World Monkeys with different color vision genotypes by examining their performance in chromatic discrimination tasks along different fixed chromatic saturation axes. Four tufted capuchin monkeys were included in the study, and their color vision genotypes were one classical protanope, one classical deuteranope, one non-classical protanope, and a normal trichromat. During the experiments, the monkeys were required to perform a chromatic discrimination task using pseudoisochromatic stimuli with varying target saturations of 0.06, 0.04, 0.03, and 0.02 u'v' units. The number of errors made by the monkeys along different chromatic axes was recorded, and their performance was quantified using the binomial probability of their hits during the tests. Our results showed that dichromatic monkeys made more errors near the color confusion lines associated with their specific color vision genotypes, while the trichromatic monkey did not demonstrate any systematic errors. At high chromatic saturation, the trichromatic monkey had significant hits in the chromatic axes around the 180° chromatic axis, whereas the dichromatic monkeys had errors in colors around the color confusion lines. At lower saturation, the performance of the dichromatic monkeys became more challenging to differentiate among the three types, but it was still distinct from that of the trichromatic monkey. In conclusion, our findings suggest that high saturation conditions can be used to identify the color vision dichromatic phenotype of capuchin monkeys, while low chromatic saturation conditions enable the distinction between trichromats and dichromats. These results extend the understanding of color vision in New World Monkeys and highlight the usefulness of suprathreshold chromatic discrimination measures in exploring color vision in non-human primates.

Achromatic and chromatic contrast discrimination in patients with type 2 diabetes

Effects of type 2 diabetes on achromatic and chromatic contrast sensitivity (CS) are still controversial. In this study, we aimed to investigate CS in patients without diabetic retinopathy (no-DR) and in those with non-proliferative DR (NPDR) and proliferative DR (PDR) using psychophysical methods with transient and sustained achromatic stimuli and color patches. Achromatic CS was measured with the pulsed pedestal (PP) paradigm (7, 12, and 19 cd/m2) and pedestal-△-pedestal (P-△-P) paradigm (11.4, 18, and 28.5 cd/m2). A chromatic discrimination paradigm that assesses protan, deutan, and tritan color vision was adopted. Forty-two patients (no-DR n = 24, NPDR n = 12, PDR = 6; male n = 22, mean age = 58.1 y/o) and 38 controls (male n = 18, mean age = 53.4 y/o) participated. In patients, mean thresholds were higher than in controls and linear trends were significant in most conditions. For the PP paradigm, differences were significant in the PDR and NPDR groups in the 7 and 12 cd/m2 condition. For the P-△-P paradigm, differences were only significant in the PDR group in the 11 cd/m2 condition. Chromatic contrast loss was significant in the PDR group along the protan, deutan and tritan axes. The results suggest independent involvements of achromatic and chromatic CS in diabetic patients.

Do EnChroma glasses improve performance on clinical tests for red-green color deficiencies?

We investigated the claims of EnChroma that their notch filters aid chromatic discrimination in color-vision deficiencies (CVD). Few research studies have addressed these claims and reports are still inconclusive, mainly due to small sample sizes. We here add to previous research finding little evidence to support the benefits of EnChroma lenses. Comparing the performance of 86 well-categorized CVD observers and 24 controls on two clinical tests we report no overall improvement when EnChroma lenses were worn. In line with previous studies, our results imply an improvement in discrimination for some colors while worsening discrimination for others. A model was constructed computing discrimination changes for different groups of ideal observers corroborating our behavioral outcomes. Taken together, our results do not support the use of EnChroma notch filters for the improvement of color discrimination in CVD.

Chromatic discrimination measures in mature observers depend on the response window

Our past anecdotal evidence prompted that a longer response window (RW) in the Trivector test (Cambridge Colour Test) improved mature observers’ estimates of chromatic discrimination. Here, we systematically explored whether RW variation affects chromatic discrimination thresholds measured by the length of Protan, Deutan and Tritan vectors. We employed the Trivector test with three RWs: 3 s, 5 s, and 8 s. Data of 30 healthy normal trichromats were stratified as age groups: ‘young’ (20–29 years), ‘middle-aged’ (31–48 years), and ‘mature’ (57–64 years). We found that for the ‘young’ and ‘middle-aged’, the thresholds were comparable at all tested RWs. However, the RW effect was apparent for the ‘mature’ observers: their Protan and Tritan thresholds decreased at 8-s RW compared to 3-s RW; moreover, their Tritan threshold decreased at 5-s RW compared to 3-s RW. Elevated discrimination thresholds at shorter RWs imply that for accurate performance, older observers require longer stimulus exposure and are indicative of ageing effects manifested by an increase in critical processing duration. Acknowledging low numbers in our ‘middle-aged’ and ‘mature’ samples, we consider our study as pilot. Nonetheless, our findings encourage us to advocate a RW extension in the Trivector protocol for testing mature observers, to ensure veridical measures of their chromatic discrimination by disentangling these from other ageing effects—slowing down of both motor responses and visual processing.

Chromatic discrimination in fixed saturation levels from trichromats and subjects with congenital color vision deficiency

Color vision tests use estimative of threshold color discrimination or number of correct responses to evaluate performance in chromatic discrimination tasks. Both approaches have advantages and disadvantages. In the present investigation, we compared the number of errors during color discrimination task in normal trichromats and participants with color vision deficiency (CVD) using pseudoisochromatic stimuli at fixed saturation levels. We recruited 28 normal trichromats and eight participants with CVD. Cambridge Color Test was used to categorize their color vision phenotype, and those with a phenotype suggestive of color vision deficiency had their L- and M-opsin genes genotyped. Pseudoisochromatic stimuli were shown with target chromaticity in 20 vectors radiating from the background chromaticity and saturation of 0.06, 0.04, 0.03, 0.02, 0.01, and 0.005 u’v' units. Each stimulus condition appeared in four trials. The number of errors for each stimulus condition was considered an indicator of the participant's performance. At high chromatic saturation, there were fewer errors from both phenotypes. The errors of the normal trichromats had no systematic variation for high saturated stimuli, but below 0.02 u’v' units, there was a discrete prevalence of tritan errors. For participants with CVD, the errors happened mainly in red-green chromatic vectors. A three-way ANOVA showed that all factors (color vision phenotype, stimulus saturation, and chromatic vector) had statistically significant effects on the number of errors and that stimulus saturation was the most important main effect. ROC analysis indicated that the performance of the fixed saturation levels to identify CVD was better between 0.02 and 0.06 u’v’ units reaching 100%, while saturation of 0.01 and 0.005 u’v’ units decreased the accuracy of the screening of the test. We concluded that the color discrimination task using high saturated stimuli separated normal trichromats and participants with red-green color vision deficiencies with high performance, which can be considered a promising method for new color vision tests based in frequency of errors.

Chromatic Discrimination Towards the Confusion Points

Abstract In this paper chromatic discrimination thresholds of normal colour-observers are analysed. Measurements were obtained with the Cambridge Colour Test, in different reference points. The results show differences in terms of the reference chromaticities. Reference points within the gamut of a CRT display were found where thresholds of normal colour observers measured towards the confusion points exceeded the normative upper threshold limit of normal colour observers. The discrimination thresholds estimated towards the confusion lines based on Trivector measurements exceeded the thresholds estimated by the Ellipse tests. Our results indicate that in case of determination of discrimination ellipses, measurements towards the confusion points are recommended.

The Effect of the Field of Adaptation on Chromatic Discrimination Ellipses

In this paper results of chromatic discrimination measurements obtained in two lighting scenarios are compared. Chromatic discrimination thresholds were measured in relation with systematically manipulated chromaticities seen under different visual angles. In both cases the Ellipse module of the Cambridge Colour Test (CCT) was obtained binocularly by normal colour-observers. Discrimination ellipses fitted to the measured thresholds were compared in terms of the adapting chromaticity and the visual angle of the adapting stimulus. Our findings show that changes in the reference chromaticity of the CCT have stronger effect on the elongation of the chromatic discrimination ellipses compared to the effect of the adapting chromaticity obtained in a light booth.Further comparison of discrimination thresholds estimated towards the confusion directions and the corresponding radii of the Ellipse test results suggests that the reliability of the Ellipse test results depends on the relation between the measurement directions and the confusion directions.

Relationship between the Children’s Visual Function Questionnaire and psychophysical measures of visual acuity and chromaticity discrimination in older visually impaired children

The Children’s Visual Function Questionnaire (CVFQ) is an instrument to measure the impact of visual impairment in children and their families. It can be used as a research tool to verify the effectiveness of treatment, therapy, and different methods for visual stimulation and rehabilitation. The aim of this study is to describe the relationship between General Health, General Vision Health, Personality, Family Impact, and Treatment – subscales of the CVFQ and psychophysical measures of visual acuity (VA) and chromaticity discrimination (CV). This prospective, cross-sectional study was conducted at the Sensory Psychophysiology Laboratory – University of São Paulo in partnership with the Ambulatory of Visual Stimulation in the Sector of Low Vision and Visual Rehabilitation – Federal University of São Paulo. The children who participated in this study were divided into two groups: study group (SG), composed of 11 children with a diagnosis of visual impairment and mean age of 55.36 months ( SD = 16.88), and control group (CG), composed of 8 children with normal vision and mean age of 64.87 months ( SD = 13.22). Both groups underwent the application of CVFQ, were tested for VA using the Teller Acuity Cards (TAC) test, and CV using the Cambridge Colour Test program for children (CCT Kids). The result of applying the CVFQ to groups of children over 3 years, comparing SG and CG, differences were observed in the following subscales: General Vision Health ( F = 10.00, p &lt; .001); Competence ( F = 7.03, p = .030); Personality ( F = 6.48, p = .010); Total Quality of Life ( F = 11.39, p = .010). These differences show a worse score for the SG. In the VA test using TAC, the data collected in groups of children over 3 years, comparing SG and CG, differences were observed in VA RE ( F = 19.25, p &lt; .001); VA LE ( F = 25.99, p &lt; .001); VA BE ( F = 15.45, p &lt; .001). These differences show worse scores for the SG. In the CV using the CCT Kids, the data collected in groups of children over 3 years, comparing SG and CG, no statistically significant differences for protan, tritan, and deutan groups were observed. For the SG, while for children over 3 years, correlations were found for General Vision Health, Competence, Family Impact, and General Quality of Life. We conclude that there are statistically significant differences when comparing the SG with the CG for the visual function of visual acuity and chromaticity discrimination, and we also demonstrated the sensitivity in the use of CVFQ in reflect VA and CV impairments.

Differences in chromatic noise suppression of luminance contrast discrimination in young and elderly people.

Aging causes impairment of contrast sensitivity and chromatic discrimination, leading to changes in the perceptual interactions between color and luminance information. We aimed to investigate the influence of chromatic noise on luminance contrast thresholds in young and older adults. Forty participants were divided equally into Young (29.6±6.3-year-old) and Elderly Groups (57.8±6.6-year-old). They performed a luminance contrast discrimination task in the presence of chromatic noise maskers using a mosaic stimulus in a mosaic background. Four chromatic noise masking protocols were applied (protan, deutan, tritan, and no-noise protocols). We found that luminance contrast thresholds were significantly elevated by the addition of chromatic noise in both age groups (P<0.05). In the Elderly group, but not the younger group, thresholds obtained in the tritan protocol were lower than those obtained from protan and deutan protocols (P<0.05). For all protocols, the luminance contrast thresholds of elderly participants were higher than in young people (P<0.01). Tritan chromatic noise was less effective in inhibiting luminance discrimination in elderly participants.

Prediction and Inverse Design of Structural Colors of Nanoparticle Systems via Deep Neural Network.

Noniridescent and nonfading structural colors generated from metallic and dielectric nanoparticles with extraordinary optical properties hold great promise in applications such as image display, color printing, and information security. Yet, due to the strong wavelength dependence of optical constants and the radiation pattern, it is difficult and time-consuming to design nanoparticles with the desired hue, saturation, and brightness. Herein, we combined the Monte Carlo and Mie scattering simulations and a bidirectional neural network (BNN) to improve the design of gold nanoparticles’ structural colors. The optical simulations provided a dataset including color properties and geometric parameters of gold nanoparticle systems, while the BNN was proposed to accurately predict the structural colors of gold nanoparticle systems and inversely design the geometric parameters for the desired colors. Taking the human chromatic discrimination ability as a criterion, our proposed approach achieved a high accuracy of 99.83% on the predicted colors and 98.5% on the designed geometric parameters. This work provides a general method to accurately and efficiently design the structural colors of nanoparticle systems, which can be exploited in a variety of applications and contribute to the development of advanced optical materials.

Age-related changes of color visual acuity in normal eyes.

PurposeTo evaluate the age-related change in color visual acuity (CVA) in normal eyes.MethodsIn total, 162 normal eyes (162 subjects, women: 52, men: 110, age range: 15–68 years) with best-corrected visual acuity (BCVA) ≥20/13 were enrolled. Fifteen colors from the New Color Test (chroma 6) were applied to Landolt “C” rings, white point D65 was applied as background, and a luminance of 30 cd/m2 was set for both the rings and the background. These rings were used to measure the chromatic spatial discrimination acuity as the CVA value, while changing the stimulus size. Correlations of the CVA value of each color and age were evaluated. Mean CVA values of all 15 colors (logarithm of the minimum angle of resolution) were compared between age groups in 10-year increments.ResultsNine CVA values (red, yellow-red, red-yellow, green, blue-green, green-blue, purple, red-purple, and purple-red) were negatively correlated with age (all p<0.05); the remaining six (yellow, green-yellow, yellow-green, blue, purple-blue, and blue-purple), as well as BCVA were not. The age groups with the best to worst mean CVA values of 15 colors were as follows: 20–29 (mean ± standard deviation, 0.303 ± 0.113), 30–39 (0.324 ± 0.096), 10–19 (0.333 ± 0.022), 50–59 (0.335 ± 0.078), 40–49 (0.339 ± 0.096), and 60–69 (0.379 ± 0.125) years. There were statistically significant differences between mean CVA values of the following groups: 20–29 and 40–49 years; 20–29 and 60–69 years; 30–39 and 60–69 years (all p<0.01).ConclusionsThe CVA values related to the medium/long-wavelength-sensitive cones were more susceptible to aging than those related to the short-wavelength-sensitive cones. This differed from previous reports, and may be related to the difference in the range of foveal cone function evaluated with each examination.

Testing Colour Appearance Model Based UCS Using HDR, WCG and COMBVD Datasets

Two colour appearance models based UCSs, CAM16-UCS and ZCAM-QMh, were tested using HDR, WCG and COMBVD datasets. As a comparison, two widely used UCSs, CIELAB and ICTCP, were tested. Metrics of the STRESS and correlation coefficient between predicted colour differences and visual differences, together with local and global uniformity based on their chromatic discrimination ellipses, were applied to test models' performance. The two UCSs give similar performance. The luminance parametric factor kL, and power factor γ, were introduced to optimize colour-difference models. Factors kL and γ of 0.75 and 0.5, gave marked improvement to predict the HDR dataset. Factor kL of 0.3 gave significant improvement in the test of WCG dataset. In the test of COMBVD dataset, optimization provide very limited improvement.

The Effects of a Blue-Light Filtering Versus Clear Intraocular Implant on Color Appearance.

PurposeMore than a dozen studies have investigated whether blue-light filtering (BLF) intraocular lens (IOL) implants influence color vision, generally finding they do not. These studies have not tested color vision per se; rather, they have measured color vision deficiencies or chromatic discrimination. Here, we used additive trichromatic colorimetry to assess color appearance in participants with BLF and clear IOL.MethodsSeventy-six participants were recruited from two populations: older participants (n = 52) with BLF and clear IOL (n = 98 eyes; M = 67.33 ± 7.48 years; 58.8% female; 25.5% non-White), and young adult control participants (n = 24; M = 21.0 ± 5.13 years; 70.8% female; 41.5% non-White). Participants used a custom-built tricolorimeter to mix three primaries until a perceived perfect neutral white was achieved. Color appearance, expressed as chromaticity coordinates, was measured with a spectral radiometer (ILS950).ResultsBetween subjects, the BLF IOL chromaticity coordinates (x = 0.34, y = 0.35, u′ = 0.21, v′ = 0.48) were not significantly different from the clear IOL (x = 0.34, y = 0.33, u′ = 0.22, v′ = 0.48). BLF and clear IOL were also not different within-contralateral subjects (n = 21; BLF x = 0.34, y = 0.33, u′ = 0.22, v′ = 0.47; clear x = 0.34, y = 0.33, u′ = 0.21, v′ = 0.48). Both IOL groups differed from young adults (v′[0.45; P = 0.001], x[0.31; P = 0.008], and y[ 0.30, P < 0.000], but not u′[0.21]).ConclusionsOne advantage of geometric representation of color space is the ability to specify the appearance (rather than spectral composition) of any light mixture by specific coordinates. Using this system, only minor differences in color appearance were found between a BLF, clear IOL, and young natural lens.Translational RelevanceWhen color perception is directly measured, the BLF and clear IOL are not meaningfully different.

Simultaneous Expression of UV and Violet SWS1 Opsins Expands the Visual Palette in a Group of Freshwater Snakes.

Snakes are known to express a rod visual opsin and two cone opsins, only (SWS1, LWS), a reduced palette resulting from their supposedly fossorial origins. Dipsadid snakes in the genus Helicops are highly visual predators that successfully invaded freshwater habitats from ancestral terrestrial-only habitats. Here, we report the first case of multiple SWS1 visual pigments in a vertebrate, simultaneously expressed in different photoreceptors and conferring both UV and violet sensitivity to Helicops snakes. Molecular analysis and in vitro expression confirmed the presence of two functional SWS1 opsins, likely the result of recent gene duplication. Evolutionary analyses indicate that each sws1 variant has undergone different evolutionary paths with strong purifying selection acting on the UV-sensitive copy and dN/dS ∼1 on the violet-sensitive copy. Site-directed mutagenesis points to the functional role of a single amino acid substitution, Phe86Val, in the large spectral shift between UV and violet opsins. In addition, higher densities of photoreceptors and SWS1 cones in the ventral retina suggest improved acuity in the upper visual field possibly correlated with visually guided behaviors. The expanded visual opsin repertoire and specialized retinal architecture are likely to improve photon uptake in underwater and terrestrial environments, and provide the neural substrate for a gain in chromatic discrimination, potentially conferring unique color vision in the UV–violet range. Our findings highlight the innovative solutions undertaken by a highly specialized lineage to tackle the challenges imposed by the invasion of novel photic environments and the extraordinary diversity of evolutionary trajectories taken by visual opsin-based perception in vertebrates.

Chromatic Discrimination Thresholds as a Function of Color Differences and Cone Excitations

In this paper, Just Noticeable Differences (JNDs) of color-normal subjects measured towards the Protan, Deutan, and Tritan confusion points are presented as a function of the chromaticity of the reference points. Measurements were executed with the Cambridge Colour Test Trivector test in equidistant reference points towards eight directions equally spaced and centered on the neutral reference point in the CIE 1976 UCS diagram.Results were evaluated as the function of the distance between the reference points and the neutral point. The reference points were the chromaticities of the backgrounds of the pseudoisochromatic plates in the test, and the neutral point was defined as equal energy white. The evaluation was performed considering ∆Eu'v' differences and L/(L + M) and S/(L + M) ratios of the cone-excitations.Chromatic discrimination thresholds exceeded the normative upper limit of color normal subjects in ∆Eu'v' units at extreme reference points. Shifting the reference points from the neutral point towards the confusion points indicated an increase of Just Noticeable Differences measured towards the confusion points following second-order polynomials. Based on our results a model estimating the JNDs expressed in ∆Eu'v' units towards the confusion points was recommended.Even though CIE 1976 UCS diagram is not a perceptually uniform color space, the Just Noticeable Differences measured with the CCT correlate with the corresponding L' and S' cone excitations. This confirms the basic applicability of the CIE 1976 UCS diagram for characterizing Just Noticeable Differences. For complete perceptual analysis, the use of cone-excitation-based metrics is still essential and recommended.