Daltonization or colour enhancement: potential uses and limitations [Invited].

The main perceptual-cognitive limitations of CDOs (Colour Deficient Observers) are analysed, along with the uses and limitations of tools that either transform images so that CNOs (Colour Normal Observers) see them as CDOs (simulation) or transform images so that CDOs can use them as CNOs (daltonization). The four main uses of colour (comparative, denotative, connotative, and aesthetic) are analysed, along with their relation to, alternatively, the ability to discriminate colour stimuli or to categorize colours. These uses of colour are applied to analyse the possible effects of daltonization tools.

Coloured filters can simulate colour deficiency in normal vision but cannot compensate for congenital colour vision deficiency.

Red-green colour vision deficiency (CVD) affects ~ 4% of Caucasians. Notch filters exist to simulate CVD when worn by colour vision normal (CVN) observers (simulation tools), or to improve colour discrimination when worn by CVD observers (compensation tools). The current study assesses effects of simulation (Variantor) and compensation (EnChroma) filters on performance in a variety of tasks. Experiments were conducted on 20 CVN and 16 CVD participants under no-filter and filter conditions (5 CVN used Variantor; 15 CVN and 16 CVD used EnChroma). Participants were tested on Ishihara and Farnsworth-Munsell 100 hue tests, CVA-UMinho colour discrimination and colour naming tasks and a board-game colour-sorting task. Repeated-measures ANOVAs found Variantor filters to significantly worsen CVN performance, mimicking protanopia. Mixed-model and repeated-measures ANOVAs demonstrate that EnChroma filters do not significantly enhance performance in CVD observers. Key EnChroma results were replicated in 8 CVD children (Ishihara test) and a sub-sample of 6 CVD adults (CVA-UMinho colour discrimination and colour naming tasks) for a smaller stimulus size. Pattern similarity exists across hue for discrimination thresholds and naming errors. Variantor filters are effective at mimicking congenital colour vision defects in CVN observers for all tasks, however EnChroma filters do not significantly compensate for CVD in any.

ColourSpot, a novel gamified tablet-based test for accurate diagnosis of color vision deficiency in young children.

There is a need for a straightforward, accessible and accurate pediatric test for color vision deficiency (CVD). We present and evaluate ColourSpot, a self-administered, gamified and color calibrated tablet-based app, which diagnoses CVD from age 4. Children tap colored targets with saturations that are altered adaptively along the three dichromatic confusion lines. Two cohorts (Total, N = 772; Discovery, N = 236; Validation, N = 536) of 4-7-year-old boys were screened using the Ishihara test for Unlettered Persons and the Neitz Test of Color Vision. ColourSpot was evaluated by testing any child who made an error on the Ishihara Unlettered test alongside a randomly selected control group who made no errors. Psychometric functions were fit to the data and "threshold ratios" were calculated as the ratio of tritan to protan or deutan thresholds. Based on the threshold ratios derived using an optimal fitting procedure that best categorized children in the discovery cohort, ColourSpot showed a sensitivity of 1.00 and a specificity of 0.97 for classifying CVD against the Ishihara Unlettered in the independent validation cohort. ColourSpot was also able to categorize individuals with ambiguous results on the Ishihara Unlettered. Compared to the Ishihara Unlettered, the Neitz Test generated an unacceptably high level of false positives. ColourSpot is an accurate test for CVD, which could be used by anyone to diagnose CVD in children from the start of their education. ColourSpot could also have a wider impact: its interface could be adapted for measuring other aspects of children's visual performance.

"Red-Green" or "Brown-Green" Dichromats? The Accuracy of Dichromat Basic Color Terms Metacognition Supports Denomination Change.

Two experiments compared "Red-Green" (R-G) dichromats' empirical and metacognized capacities to discriminate basic color categories (BCCs) and to use the corresponding basic color terms (BCTs). A first experiment used a 102-related-colors set for a pointing task to identify all the stimuli that could be named with each BCT by each R-G dichromat type (8 protanopes and 9 deuteranopes). In a second experiment, a group of R-G dichromats (15 protanopes and 16 deuteranopes) estimated their difficulty discriminating BCCs-BCTs in a verbal task. The strong coincidences between the results derived from the pointing and the verbal tasks indicated that R-G dichromats have very accurate metacognition about their capacities (they only had considerable difficulty discriminating 13 out of the total of 55 possible BCT pairs) and limitations (Brown-Green and Blue-Purple pairs were rated especially difficult to differentiate) in the use of BCTs. Multidimensional scaling (MDS) solutions derived from both tasks were very similar: BCTs in R-G dichromats were properly represented in 2D MDS solutions that clearly show one chromatic dimension and one achromatic dimension. Important concordances were found between protanopes and deuteranopes. None of these dichromats showed substantial difficulty discriminating the Red-Green pair. So, to name them "R-G" dichromats is misleading considering their empirical capacities and their metacognition. Further reasons to propose the use of the alternative denomination "Brown-Green" dichromats are also discussed. We found some relevant differences between the "Brown-Green" dichromats' empirical and self-reported difficulties using BCTs. Their metacognition can be considered a "caricature" of their practical difficulties. This caricature omits some difficulties including their problems differentiating "white" and "black" from other BCTs, while they overestimate their limitations in differentiating the most difficult pairs (Brown-Green and Blue-Purple). Individual differences scaling (INDSCAL) analyses indicated that the metacognition regarding the use of BCTs in "Brown-Green" dichromats, especially deuteranopes, is driven slightly more by the chromatic dimension and driven slightly less by the achromatic dimension, than their practical use of BCTs. We discuss the relevance of our results in the framework of the debate between the linguistic relativity hypothesis (LRH) and the universal evolution (UE) theories.

Basic Color Terms (BCTs) and Categories (BCCs) in Three Dialects of the Spanish Language: Interaction Between Cultural and Universal Factors.

Two experiments were performed to identify and compare the Basic Color Terms (BCTs) and the Basic Color Categories (BCCs) included in three dialects (Castilian, Mexican, and Uruguayan) of the Spanish language. Monolexemic Elicited lists were used in the first experiment to identify the BCTs of each dialect. Eleven BCTs appeared for the Spanish and the Mexican, and twelve did so for the Uruguayan. The six primary BCTs (rojo "red," verde "green," amarillo "yellow," azul "blue," negro "black," and blanco "white") appeared in the three dialects. This occurred for only three derived BCTs (gris "gray," naranja "orange," and rosa "pink") but not for the other five derived BCTs (celeste "sky blue," marrón "brown," café "brown," morado "purple," and violeta "purple"). Color transitions were used in the second experiment for two different tasks. Extremes naming task was used to determine the relation between two different dialects' BCTs: equality, equivalence or difference. The results provided the first evidence for marrón "brown" and café "brown" being equivalent terms for the same BCC (brown in English) as is the case of morado "purple" and violeta "purple." Uruguayan celeste "sky blue" had no equivalent BCT in the other two dialects. Boundary delimitation task required the selection of the color in the boundary between two categories. The task was used to reasonably estimate the volume occupied by each BCC in the color space considering its chromatic area and lightness range. Excluding sky blue (celeste "sky blue") and blue (azul "blue"), the other BCCs color volumes were similar across the three dialects. Uruguayan sky blue and blue volumes conjointly occupied the portion of the color space corresponding to the Castilian and Mexican blue BCC. The fact that the BCT celeste "sky blue" only appeared in Uruguayan very probably derived from specific cultural factors (the use of the color in the flags and the arrival of an important number of Italian immigrants). Nevertheless, these cultural factors seem to nurture from a perceptive structuring of the color space, which nature is universal, as the boundaries of this category can be delimited from the responses of Spanish and Mexican participants.

Robust colour constancy in red-green dichromats.

Colour discrimination has been widely studied in red-green (R-G) dichromats but the extent to which their colour constancy is affected remains unclear. This work estimated the extent of colour constancy for four normal trichromatic observers and seven R-G dichromats when viewing natural scenes under simulated daylight illuminants. Hyperspectral imaging data from natural scenes were used to generate the stimuli on a calibrated CRT display. In experiment 1, observers viewed a reference scene illuminated by daylight with a correlated colour temperature (CCT) of 6700K; observers then viewed sequentially two versions of the same scene, one illuminated by either a higher or lower CCT (condition 1, pure CCT change with constant luminance) or a higher or lower average luminance (condition 2, pure luminance change with a constant CCT). The observers' task was to identify the version of the scene that looked different from the reference scene. Thresholds for detecting a pure CCT change or a pure luminance change were estimated, and it was found that those for R-G dichromats were marginally higher than for normal trichromats regarding CCT. In experiment 2, observers viewed sequentially a reference scene and a comparison scene with a CCT change or a luminance change above threshold for each observer. The observers' task was to identify whether or not the change was an intensity change. No significant differences were found between the responses of normal trichromats and dichromats. These data suggest robust colour constancy mechanisms along daylight locus in R-G dichromacy.

Assessing the effects of dynamic luminance contrast noise masking on a color discrimination task.

The aim of this work was to assess the influence of dynamic luminance contrast noise masking (LCNM) on color discrimination for color normal and anomalous trichromats. The stimulus was a colored target on a background presented on a calibrated CRT display. In the static LCNM condition, the background and target consisted of packed circles with variable size and static random luminance. In the dynamic LCNM condition, a 10 Hz square luminance signal was added to each circle. The phase of this signal was randomized across circles. Discrimination thresholds were estimated along 20 hue directions concurrent at the color of the background. Six observers with normal color vision, six deuteranomalous observers, and three protanomalous observers performed the test in both conditions. With dynamic LCNM, thresholds were significantly lower for anomalous observers but not for normal observers, suggesting a facilitation effect of the masking for anomalous trichromats.

Color preference in red-green dichromats.

Around 2% of males have red-green dichromacy, which is a genetic disorder of color vision where one type of cone photoreceptor is missing. Here we investigate the color preferences of dichromats. We aim (i) to establish whether the systematic and reliable color preferences of normal trichromatic observers (e.g., preference maximum at blue, minimum at yellow-green) are affected by dichromacy and (ii) to test theories of color preference with a dichromatic sample. Dichromat and normal trichromat observers named and rated how much they liked saturated, light, dark, and focal colors twice. Trichromats had the expected pattern of preference. Dichromats had a reliable pattern of preference that was different to trichromats, with a preference maximum rather than minimum at yellow and a much weaker preference for blue than trichromats. Color preference was more affected in observers who lacked the cone type sensitive to long wavelengths (protanopes) than in those who lacked the cone type sensitive to medium wavelengths (deuteranopes). Trichromats' preferences were summarized effectively in terms of cone-contrast between color and background, and yellow-blue cone-contrast could account for dichromats' pattern of preference, with some evidence for residual red-green activity in deuteranopes' preference. Dichromats' color naming also could account for their color preferences, with colors named more accurately and quickly being more preferred. This relationship between color naming and preference also was present for trichromat males but not females. Overall, the findings provide novel evidence on how dichromats experience color, advance the understanding of why humans like some colors more than others, and have implications for general theories of aesthetics.

An experimental method for the assessment of color simulation tools.

The Simulcheck method for evaluating the accuracy of color simulation tools in relation to dichromats is described and used to test three color simulation tools: Variantor, Coblis, and Vischeck. A total of 10 dichromats (five protanopes, five deuteranopes) and 10 normal trichromats participated in the current study. Simulcheck includes two psychophysical tasks: the Pseudoachromatic Stimuli Identification task and the Minimum Achromatic Contrast task. The Pseudoachromatic Stimuli Identification task allows determination of the two chromatic angles (h(uv) values) that generate a minimum response in the yellow­blue opponent mechanism and, consequently, pseudoachromatic stimuli (greens or reds). The Minimum Achromatic Contrast task requires the selection of the gray background that produces minimum contrast (near zero change in the achromatic mechanism) for each pseudoachromatic stimulus selected in the previous task (L(R) values). Results showed important differences in the colorimetric transformations performed by the three evaluated simulation tools and their accuracy levels. Vischeck simulation accurately implemented the algorithm of Brettel, Viénot, and Mollon (1997). Only Vischeck appeared accurate (similarity in huv and L(R) values between real and simulated dichromats) and, consequently, could render reliable color selections. It is concluded that Simulcheck is a consistent method because it provided an equivalent pattern of results for huv and L(R) values irrespective of the stimulus set used to evaluate a simulation tool. Simulcheck was also considered valid because real dichromats provided expected huv and LR values when performing the two psychophysical tasks included in this method.

Basic color terms use by aged observers: lens aging and perceptual compensation.

Basic Color Terms (BCTs) use by aged people (normal and tritanomalous) was analysed on the basis of the results provided by two visual search tasks. One task (mapping) required participants to select every stimulus that could be included in a specific BCT. Another task (best representative) required participants to select the stimulus that most accurately identified a BCT. Both tasks' results were used for two different goals. First (descriptive level), to specify the main differences between aged and young people in their use of BCTs (dimensions provided by multidimensional scaling, confusions between specific pairs of BCTs). Second (explicative level), to compare the accuracy of three models for predicting aged people's performance. Model A (filtering without compensation) assumed that aged people must use BCTs as young people do when responding to stimuli similar to the ones produced by lens aging. On the contrary, model B (filtering with compensation) assumed that lens aging effects were partially compensated by a von Kries-type mechanism (white normalisation). Finally, model C (tritan lines) assumed that ocular aging only influences S cone responses (tritan responses). Results showed that model B was the most accurate with the percentage of explained variance over 90% for both aged groups.

Basic Color Terms Use by Aged observers: lens aging and perceptual compensation

Basic Color Terms (BCTs) use by aged people (normal and tritanomalous) was analysed on the basis of the results provided by two visual search tasks. One task (mapping) required participants to select every stimulus that could be included in a specific BCT. Another task (best representative) required participants to select the stimulus that most accurately identified a BCT. Both tasks’ results were used for two different goals. First (descriptive level), to specify the main differences between aged and young people in their use of BCTs (dimensions provided by multidimensional scaling, confusions between specific pairs of BCTs). Second (explicative level), to compare the accuracy of three models for predicting aged people’s performance. Model A (filtering without compensation) assumed that aged people must use BCTs as young people do when responding to stimuli similar to the ones produced by lens aging. On the contrary, model B (filtering with compensation) assumed that lens aging effects were partially compensated by a von Kries-type mechanism (white normalisation). Finally, model C (tritan lines) assumed that ocular aging only influences S cone responses (tritan responses). Results showed that model B was the most accurate with the percentage of explained variance over 90 % for both aged groups (AU)

Los resultados proporcionados por dos tareas de búsqueda visual sirvieron para analizar el uso de los términos básicos de color (TBCs) en personas mayores (normales y tritanómalas). Una tarea (delimitación) requirió que los participantes seleccionasen todos los estímulos que podían incluirse en cada TBC concreto. La otra tarea (mejor representante) requirió que seleccionasen el estímulo que mejor identificaba a un TBC. Los resultados de ambas tareas se utilizaron con dos finalidades diferentes. La primera (nivel descriptivo) fue la de especificar las diferencias principales entre las personas mayores y jóvenes en su forma de usar los TBCs (dimensiones proporcionadas por el escalamiento multidimensional, confusiones entre pares específicos de TBCs). La segunda (nivel explicativo) fue la de comparar la adecuación de tres modelos para predecir el desempeño de las personas mayores. El modelo A (filtrado sin compensación) asumió que las personas mayores debían usar los TBCs como lo hacen las personas jóvenes al responder a estímulos similares a los que produce el envejecimiento del cristalino. Por el contrario, el modelo B (filtrado con compensación) asumió que los efectos del envejecimiento del cristalino fueron parcialmente compensados por un mecanismo tipo von Kries (normalización al blanco). Finalmente el modelo C (líneas tritán) asumió que el envejecimiento del cristalino sólo influye en las respuestas de los conos S (respuestas tritán). Los resultados mostraron que el modelo B fue el más adecuado, ya que llegó a explicar más del 90% de la varianza en ambos grupos de personas mayores (AU)