Visual Performance of People With Albinism Assessed With Generalizable and Adaptive AIM and FInD Methods.

Purpose: People with albinism (PwA) are known to have visual impairments; however, little is known about whether these functions are disrupted across earlier and later stages of the visual pathway. We investigated distinct perceptual functions and fixation stability within each observer and compared the data with age- (±5 years) and sex-matched controls. Methods: Twenty-one self-reported PwA and twenty-one controls were recruited. Angular-indication measurement (AIM) and foraging-interactive-D-prime (FInD) psychophysical methods were deployed to measure OS, OD, and OU near visual acuity, spatial contrast sensitivity function (CSF), temporal contrast sensitivity (tCS; 0.5 c/°; horizontal grating: 0, 1, 2, 4, and 8 Hz), OU glare acuity, threshold-versus-contrast (2c/° vertical grating), long, medium, and short wavelength cone-isolated color detection, color discrimination, stereoacuity across spatial frequencies (1c/°, 2c/°, 4c/°, 8c/°), horizontal, circular, radial pattern and motion coherence, and equivalent-noise motion detection. Thresholds were determined by AIM and FInD and compared using N-ANOVAs, t-tests, planned multi-comparisons, correlations, and unsupervised, agglomerative hierarchical cluster analysis for each group. Results: We found significant differences between groups for most visual functions except for simple and complex form-coherence (two way-ANOVAs, P > 0.05) and complex motion coherence. Correlations between outcomes revealed more significant correlations for PwA and differences in the specific correlates between groups. Unsupervised hierarchical clustering revealed different functional clusters between groups. Conclusions: AIM and FInD successfully interrogated visual deficits in PwA. Overall, PwA showed impaired performance in achromatic, chromatic, temporal, and binocular functions, and had higher intrinsic noise levels. Midlevel vision was comparable between groups. Unsupervised cluster analysis and correlation between outcomes revealed a difference in functional outcome clusters between groups. The results may help to increase the efficiency of screening and identify target deficits for rehabilitation.

Focusing on mixed narrow band stimuli: Implications for mechanisms of accommodation and displays.

The eye has considerable chromatic aberration, meaning that the accommodative demand varies with wavelength. Given this, how does the eye accommodate to light of differing spectral content? Previous work is not conclusive but, in general, the eye focuses in the center of the visible spectrum for broadband light, and it focuses at a distance appropriate for individual wavelengths for narrowband light. For stimuli containing two colors, there are also mixed reports. This is the second of a series of two papers where we investigate accommodation in relation to chromatic aberration Fernandez-Alonso, Finch, Love, and Read (2024). In this paper, for the first time, we measure how the eye accommodates to images containing two narrowband wavelengths, with varying relative luminance under monocular conditions. We find that the eye tends to accommodate between the two extremes, weighted by the relative luminance. At first sight, this seems reasonable, but we show that image quality would be maximized if the eye instead accommodated on the more luminous wavelength. Next we explore several hypotheses as to what signal the eye might be using to drive accommodation and compare these with the experimental data. We show that the data is best explained if the eye seeks to maximize contrast at low spatial frequencies. We consider the implication of these results for both the mechanism behind accommodation, and for modern displays containing narrowband illuminants.

Color and brightness at work: Shedding some light on mind wandering.

INTRODUCTION: Occupational hazards are partly caused by the physical factors of the work environment, among which are ambient color and brightness, which can interfere with cognitive performance. Especially in modern work environments, performance relies heavily on cognitive functions such as attention, and an important factor in disrupting sustained attention is mind wandering (MW). This study aimed to investigate the effects of white and blue colors with two brightness levels on sustained attention and brain electrophysiology. METHODS: A total of 20 participants were exposed to 4 different conditions (white and blue as color and 300 and 800 lx as the brightness level) in separate blocks in a virtual reality environment in which a continuous performance test (CPT) was performed. RESULTS: The high brightness blue condition induced significant changes in sustained attention. MW network analysis showed a significant decrease in delta frequency band in the blue color condition with high brightness and beta decrease in the blue color condition with low brightness, whereas the activity of MW network increased when exposed to the white color condition. CONCLUSION: High-brightness blue light resulted in better sustained attention and decreased activity of MW-related neural regions. It is thus recommended that these results be taken into consideration in the interior design of educational settings and cars among other environments that require a high level and maintenance of cognitive functions, especially sustained attention.

Color category and inter-item interaction influence color working memory codependently.

Our brains do not always encode visual information in a veridical way. Visual working memory (WM) for features such as color can be biased. WM bias comes from several sources. Category priors can lead to WM bias. For example, color WM is biased toward or away from category prototypes. In addition to category knowledge, contextual factors can induce and modulate WM bias; however, these biases of different sources have usually been investigated independently with different tasks. The present study sought to explore how color WM is influenced by both color category and concurrent distractor. Specifically, we asked participants to retain two color items in WM to investigate how the WM representation of the target color is biased by learned category knowledge and contextual inter-item interactions. Our study found that the WM representation of the target color is biased toward or away from the category prototypes and away from the distractor color that is simultaneously held in WM, indicating that both color category and concurrent distractor bias color WM. More importantly, the weight of these two biases depends on the specific color category, suggesting that category priors and inter-item interaction biases are not simply additive but flexible. Furthermore, we revealed that both types of biases arise from perceptual processes.

Chromatic processing and receptive-field structure in neurons of the anterior optic tract of the honeybee brain.

Color vision in honeybees is a well-documented perceptual phenomenon including multiple behavioral tests of trichromaticity and color opponency. Data on the combined color/space properties of high order visual neurons in the bee brain is however limited. Here we fill this gap by analyzing the activity of neurons in the anterior optic tract (AOT), a high order brain region suggested to be involved in chromatic processing. The spectral response properties of 72 units were measured using UV, blue and green light stimuli presented in 266 positions of the visual field. The majority of these units comprise combined chromatic-spatial processing properties. We found eight different neuron categories in terms of their spectral, spatial and temporal response properties. Color-opponent neurons, the most abundant neural category in the AOT, present large receptive fields and activity patterns that were typically opponent between UV and blue or green, particularly during the on-tonic response phase. Receptive field shapes and activity patterns of these color processing neurons are more similar between blue and green, than between UV and blue or green. We also identified intricate spatial antagonism and double spectral opponency in some receptive fields of color-opponent units. Stimulation protocols with different color combinations applied to 21 AOT units allowed us to uncover additional levels of spectral antagonism and hidden inhibitory inputs, even in some units that were initially classified as broad-band neurons based in their responses to single spectral lights. The results are discussed in the context of floral color discrimination and celestial spectral gradients.

Asymmetric distribution of color-opponent response types across mouse visual cortex supports superior color vision in the sky.

Color is an important visual feature that informs behavior, and the retinal basis for color vision has been studied across various vertebrate species. While many studies have investigated how color information is processed in visual brain areas of primate species, we have limited understanding of how it is organized beyond the retina in other species, including most dichromatic mammals. In this study, we systematically characterized how color is represented in the primary visual cortex (V1) of mice. Using large-scale neuronal recordings and a luminance and color noise stimulus, we found that more than a third of neurons in mouse V1 are color-opponent in their receptive field center, while the receptive field surround predominantly captures luminance contrast. Furthermore, we found that color-opponency is especially pronounced in posterior V1 that encodes the sky, matching the statistics of natural scenes experienced by mice. Using unsupervised clustering, we demonstrate that the asymmetry in color representations across cortex can be explained by an uneven distribution of green-On/UV-Off color-opponent response types that are represented in the upper visual field. Finally, a simple model with natural scene-inspired parametric stimuli shows that green-On/UV-Off color-opponent response types may enhance the detection of 'predatory'-like dark UV-objects in noisy daylight scenes. The results from this study highlight the relevance of color processing in the mouse visual system and contribute to our understanding of how color information is organized in the visual hierarchy across species.

Colour/shape-taste correspondences across three languages in ChatGPT.

Crossmodal correspondences, the tendency for a sensory feature / attribute in one sensory modality (either physically present or merely imagined), to be associated with a sensory feature in another sensory modality, have been studied extensively, revealing consistent patterns, such as sweet tastes being associated with pink colours and round shapes across languages. The present research explores whether such correspondences are captured by ChatGPT, a large language model developed by OpenAI. Across twelve studies, this research investigates colour/shapes-taste crossmodal correspondences in ChatGPT-3.5 and -4o, focusing on associations between shapes/colours and the five basic tastes across three languages (English, Japanese, and Spanish). Studies 1A-F examined taste-shape associations, using prompts in three languages to assess ChatGPT's association of round and angular shapes with the five basic tastes. The results indicated significant, consistent, associations between shape and taste, with, for example, round shapes strongly associated with sweet/umami tastes and angular shapes with bitter/salty/sour tastes. The magnitude of shape-taste matching appears to be greater in ChatGPT-4o than in ChatGPT-3.5, and ChatGPT prompted in English and Spanish than ChatGPT prompted in Japanese. Studies 2A-F focused on colour-taste correspondences, using ChatGPT to assess associations between eleven colours and the five basic tastes. The results indicated that ChatGPT-4o, but not ChatGPT-3.5, generally replicates the patterns of colour-taste correspondences that have previously been observed in human participants. Specifically, ChatGPT-4o associates sweet tastes with pink, sour with yellow, salty with white/blue, bitter with black, and umami with red across languages. However, the magnitude/similarity of shape/colour-taste matching observed in ChatGPT-4o appears to be more pronounced (i.e., having little variance, large mean difference), which does not adequately reflect the subtle nuances typically seen in human shape/colour-taste correspondences. These findings suggest that ChatGPT captures colour/shapes-taste correspondences, with language- and GPT version-specific variations, albeit with some differences when compared to previous studies involving human participants. These findings contribute valuable knowledge to the field of crossmodal correspondences, explore the possibility of generative AI that resembles human perceptual systems and cognition across languages, and provide insight into the development and evolution of generative AI systems that capture human crossmodal correspondences.

Target-distractor similarity predicts visual search efficiency but only for highly similar features.

A major constraining factor for attentional selection is the similarity between targets and distractors. When similarity is low, target items can be identified quickly and efficiently, whereas high similarity can incur large costs on processing speed. Models of visual search contrast a fast, efficient parallel stage with a slow serial processing stage where search times are strongly modulated by the number of distractors in the display. In particular, recent work has argued that the magnitude of search slopes should be inversely proportional to target-distractor similarity. Here, we assessed the relationship between target-distractor similarity and search slopes. In our visual search tasks, participants detected an oddball color target among distractors (Experiments 1 & 2) or discriminated the direction of a triangle in the oddball color (Experiment 3). We systematically varied the similarity between target and distractor colors (along a circular CIELAB color wheel) and the number of distractors in the search array, finding logarithmic search slopes that were inversely proportional to the number of items in the array. Surprisingly, we also found that searches were highly efficient (i.e., near-zero slopes) for targets and distractors that were extremely similar (≤20° in color space). These findings indicate that visual search is systematically influenced by target-distractor similarity across different processing stages. Importantly, we found that search can be highly efficient and entirely unaffected by the number of distractors despite high perceptual similarity, in contrast to the general assumption that high similarity must lead to slow and serial search behavior.

Parallel gain modulation mechanisms set the resolution of color selectivity in human visual cortex.

Color discrimination is fundamental to human behavior. We find bananas by coarsely searching for yellow but then differentiate nuances of yellow to pick the best exemplars. How does the brain adjust the resolution of color selectivity to our changing needs? Here, we analyze the brain magnetic response in the human visual cortex to show that color selectivity is adaptively set by coarse- and fine-resolving processes running in parallel at different hierarchical levels. Those include a gain enhancement in the higher-lever cortex of color units tuned away from the target to resolve very similar colors and a coarsely resolving gain enhancement in the mid-level cortex of units tuned to the target. Our findings suggest that attention operates on a form of multiresolution representation of color at different levels in the visual hierarchy, which keeps selectivity adaptive to a changing resolution context.

A circuit motif for color in the human foveal retina.

The neural pathways that start human color vision begin in the complex synaptic network of the foveal retina where signals originating in long (L), middle (M), and short (S) wavelength-sensitive cone photoreceptor types are compared through antagonistic interactions, referred to as opponency. In nonhuman primates, two cone opponent pathways are well established: an L vs. M cone circuit linked to the midget ganglion cell type, often called the red-green pathway, and an S vs. L + M cone circuit linked to the small bistratified ganglion cell type, often called the blue-yellow pathway. These pathways have been taken to correspond in human vision to cardinal directions in a trichromatic color space, providing the parallel inputs to higher-level color processing. Yet linking cone opponency in the nonhuman primate retina to color mechanisms in human vision has proven particularly difficult. Here, we apply connectomic reconstruction to the human foveal retina to trace parallel excitatory synaptic outputs from the S-ON (or "blue-cone") bipolar cell to the small bistratified cell and two additional ganglion cell types: a large bistratified ganglion cell and a subpopulation of ON-midget ganglion cells, whose synaptic connections suggest a significant and unique role in color vision. These two ganglion cell types are postsynaptic to both S-ON and L vs. M opponent midget bipolar cells and thus define excitatory pathways in the foveal retina that merge the cardinal red-green and blue-yellow circuits, with the potential for trichromatic cone opponency at the first stage of human vision.

Mixing and mingling in visual working memory: Inter-item competition is feature-specific during encoding and feature-general during maintenance.

Visual working memory (WM) is a central cognitive ability but is capacity-limited due to competition between remembered items. Understanding whether inter-item competition depends on the similarity of the features being remembered has important implications for determining if competition occurs in sensory or post-sensory stages of processing. Experiment 1 compared the precision of WM across homogeneous displays, where items belonged to the same feature type (e.g., colorful circles), and heterogeneous displays (e.g., colorful circles and oriented bars). Performance was better for heterogeneous displays, suggesting a feature-specific component of interference. However, Experiment 2 used a retro-cueing task to isolate encoding from online maintenance and revealed that inter-item competition during storage was not feature-specific. The data support recent models of WM in which inter-item interference - and hence capacity limits in WM - occurs in higher-order structures that receive convergent input from a diverse array of feature-specific representations.

Physical effort modulates perceptual awareness judgment independent of level of processing.

Recent studies have emphasized the association between action and perceptual awareness, suggesting that action-related information can contribute to perceptual awareness. Given that the Level of Processing (LoP) hypothesis proposes that the emergence of awareness depends on the level of stimulus processing, the current study examines whether action impacts perceptual awareness across different processing levels. In Experiment 1, participants identified target stimuli's color (low-level task) or category (high-level task) via mouse clicks, followed by visual awareness ratings. Experiment 2 replicated the tasks using hand-grip dynamometers. Results from Experiment 1 support the LoP theory, showing a more gradual emergence of awareness for low-level features and a more dichotomous emergence for high-level features. In Experiment 2, higher reported visual awareness ratings were observed at greater physical effort, regardless of task type. These results suggest that action-related information influences reported awareness of stimuli in the same way at low- and high-level stimulus processing.

Search flavor labels in beverages: An electrophysiological investigation of color-flavor congruency and association strength in visual search.

Individuals are apt to link various characteristics of an object or event through different sensory experiences. We conducted two electrophysiological experiments to investigate the effects of color-flavor congruency and association strength on visual search efficiency and the in-depth cognitive mechanisms underlying multisensory processes. Participants were prompted with a flavor label and asked to identify the primed flavor from four beverage bottle images. Experiment 1 focused on color-flavor congruency and noted faster searches for congruent targets than incongruent ones. EEG data exhibited smaller N2, larger P3 and LPC, and increased parietal-occipital midline (POM) alpha power for incongruent targets than congruent ones. Experiment 2 manipulated color-flavor association strength within each flavor. Behavioral findings showed that searches for targets with weak association strength took longer than those with strong association strength. Moreover, time-frequency analysis displayed that the former evoked greater frontal midline (FM) theta power and higher alpha power than the latter. Altogether, our research indicated that (1) color expectations based on prior experience can automatically guide people's attentional selection, (2) the color-flavor congruency and association strength impact the visual search efficiency via distinct pathways, and (3) theta and alpha activities make a pivotal role in unraveling multisensory information processing. These findings shed some light on the intricate cognitive processes involved in crossmodal visual search and the underlying neurocognitive dynamics.

The influence of task-irrelevant color perception on flanker task performance: Insights from behavioral and ERP data.

Perception of color as a task-relevant stimulus can affect cognition and behavior in the flanker task; however, it remains unclear whether it has the same impact when it is a task-irrelevant stimulus dimension. To this end, we applied four-letter flanker tasks with or without colored (red/blue) to 23 healthy young adults, while recording the event-related potentials (ERPs) and behavioral performance. The flanker task included four kinds of color types: non-color letter (NC), all color letter (AC), flanker color letter (FC), and target color letter (TC), each flanker task included congruent and incongruent conditions. The behavioral data demonstrated the classic conflict effect across all color types of flanker tasks in both reaction times (RTs) and accuracy, the significant interaction and main effect of color type factors were only observed in accuracy. The ERP results showed significant interaction between conflict factor (congruent, incongruent) and color type (NC, AC, FC, and TC), and the color type factor enhanced the fronto-central P2 (180-200 ms), descended the fronto-centro-parietal N2b (260-320 ms), and increased the fronto-central P3b (360-520 ms). The fronto-central P2 and the fronto-central P3b were larger for TC than NC, AC, and FC in the congruent condition, while the fronto-central P3b was smaller for NC than AC, FC, and TC in the incongruent condition. Furthermore, the fronto-centro-parietal N2b was decreased successively in NC, AC, FC, and TC in both congruent and incongruent conditions. Overall, our findings suggested that the task-irrelevant stimuli dimension of color can capture some attentional resources and is affected by the location of color (target/flanker) and the type of task trial (congruent/incongruent) in the flanker task.

Psychophysics of neon color spreading: Chromatic and temporal factors are not limiting.

Neon color spreading (NCS) is an illusory color phenomenon that provides a dramatic example of surface completion and filling-in. Numerous studies have varied both spatial and temporal aspects of the neon-generating stimulus to explore variations in the strength of the effect. Here, we take a novel, parametric, low-level psychophysical approach to studying NCS in two experiments. In Experiment 1, we test the ability of both cone-isolating and equiluminant stimuli to generate neon color spreading for both increments and decrements in cone modulations. As expected, sensitivity was low to S(hort-wavelength) cone stimuli due to their poor spatial resolution, but sensitivity was similar for the other color directions. We show that when these differences in detection sensitivity are accounted for, the particular cone type, and the polarity (increment or decrement), make little difference in generating neon color spreading, with NCS visible at about twice detection threshold level in all cases. In Experiment 2, we use L-cone flicker modulations (reddish and greenish excursions around grey) to study sensitivity to NCS as a function of temporal frequency from 0.5 to 8 Hz. After accounting for detectability, the temporal contrast sensitivity functions for NCS are approximately constant or even increase over the studied frequency range. Therefore there is no evidence in this study that the processes underlying NCS are slower than the low-level processes of simple flicker detection. These results point to relatively fast mechanisms, not slow diffusion processes, as the substrate for NCS.

Bridging instrumental and visual perception with improved color difference equations: A multi-center study.

OBJECTIVES: This multicenter study aimed to evaluate visual-instrumental agreement of six color measurement devices and optimize three color difference equations using a dataset of visual color differences (∆V) from expert observers. METHODS: A total of 154 expert observers from 16 sites across 5 countries participated, providing visual scaling on 26 sample pairs of artificial teeth using magnitude estimation. Three color difference equations (ΔE*ab, ∆E00, and CAM16-UCS) were tested. Optimization of all three equations was performed using device-specific weights, and the standardized residual sum of squares (STRESS) index was used to evaluate visual-instrumental agreement. RESULTS: The ΔE*ab formula exhibited STRESS values from 18 to 40, with visual-instrumental agreement between 60 % and 82 %. The ∆E00 formula showed STRESS values from 26 to 32, representing visual-instrumental agreement of 68 % to 74 %. CAM16-UCS demonstrated STRESS values from 32 - 39, with visual-instrumental agreement between 61-68 %. Following optimization, STRESS values decreased for all three formulas, with ΔE' demonstrating average visual-instrumental agreement of 79 % and ∆E00 of 78 %. CAM16-UCS showed average visual-instrumental agreement of 76 % post optimization. SIGNIFICANCE: Optimization of color difference equations notably improved visual-instrumental agreement, overshadowing device performance. The optimzed ΔE' formula demonstrated the best overall performance combining computational simplicty with outstanding visual-instrumental agreement.

Increased color preference through the introduction of luminance noise in chromatic stimuli.

Humans exhibit consistent color preferences that are often described as a curvilinear pattern across hues. The recent literature posits that color preference is linked to the preference for objects or other entities associated with those colors. However, many studies examine this preference using isoluminant colors, which don't reflect the natural viewing experience typically influenced by different light intensities. The inclusion of random luminance levels (luminance noise) in chromatic stimuli may provide an initial step towards assessing color preference as it is presented in the real world. Employing mosaic stimuli, this study aimed to evaluate the influence of luminance noise on human color preference. Thirty normal trichromats engaged in a two-alternative forced-choice paradigm, indicating their color preferences between presented pairs. The chromatic stimuli included saturated versions of 8 standard hues, presented in mosaics with varying diameters under different luminance noise conditions. Results indicated that the inclusion of luminance noise increased color preference across all hues, specifically under the high luminance noise range, while the curvilinear pattern remained unchanged. Finally, women exhibit a greater sensitivity to the presence of luminance noise than men, potentially due to differences between men and women in aesthetic evaluation strategies.

Assessing the impact of glazing and window shade systems on view clarity.

Windows provide access to daylight and outdoor views, influencing building design. Various glazing and window shade materials are used to mitigate glare, overheating and privacy issues, and they affect view clarity. Among them, we evaluated the effect of window films, electrochromic (EC) glass, and fabric shades on view clarity. We conducted an experiment with 50 participants using visual tests adapted from clinical vision tests (visual acuity, contrast sensitivity, color sensitivity) and images displayed on a computer monitor in a controlled laboratory. Window films and EC glass tints outperformed fabric shades in visual acuity, contrast sensitivity and view satisfaction with the exception of the darkest EC tint state and dark grey VLT 3% shade for color sensitivity and view satisfaction. The EC tints pose internal reflection issues and fabric shades are preferred for visual privacy. Window films and EC glass hinder participants' blue-green color discrimination while fabric shades also decrease red-yellow color discrimination. Visual acuity predicts view satisfaction and contrast sensitivity is the strongest predictor for visual privacy. Generally, higher visible light transmittance and lower solar reflectance (darker color) enhance human visual performance. The proposed workflow provides an experimental procedure, identifies the primary variables and establishes a predictive framework for assessing view clarity of fenestration.

Perception of #TheDress in childhood is influenced by age and green-leaf preference.

The perception of the ambiguous image of #TheDress may be influenced by optical factors, such as macular pigments. Their accumulation during childhood could increase with age and the ingestion of carotenoid-containing foods. The purpose of this study was to investigate whether the visual perception of the dress in children would differ based on age and carotenoid preference. This was a cross-sectional, observational, and comparative study. A poll was administered to children aged 2 to 10 years. Parents were instructed to inquire about the color of #TheDress from their children. A carotenoid preference survey was also completed. A total of 413 poll responses were analyzed. Responses were categorized based on the perceived color of the dress: blue/black (BB) (n = 204) and white/gold (WG) (n = 209). The mean and median age of the WG group was higher than the BB group (mean 6.1, median 6.0 years, standard deviation [SD] 2.2; mean 5.5, median 5.0 years, SD 2.3; p = 0.007). Spearman correlation between age and group was 0.133 (p = 0.007). Green-leaf preference (GLP) showed a statistically significant difference between groups (Mann-Whitney U: p = 0.038). Spearman correlation between GLP and group was 0.102 (p = 0.037). Logistic regression for the perception of the dress as WG indicated that age and GLP were significant predictors (age: B weight 0.109, p = 0.012, odds ratio: 1.115; GLP: B weight 0.317, p = 0.033, odds ratio: 1.373). Older children and those with a higher GLP were more likely to perceive #TheDress as WG. These results suggest a potential relationship with the gradual accumulation of macular pigments throughout a child's lifetime.

Perceptibility and acceptability thresholds for color differences of light and dark maxillofacial skin replications.

The aim of this study was to assess the perceptibility and acceptability thresholds of maxillofacial silicones for light and dark skin colors and to evaluate the effect of gender and professional experience on these thresholds. Two different sets of specimens (as light and dark) each, consisting of 14 (25 × 25 × 6-mm3) silicone skin replications, were produced. Four specimens of each set were produced from the same silicon mixture of the relevant set and polymerized simultaneously to provide standardized fabrication conditions. These 4 light/dark specimens were assigned as "baseline color specimens (BCs)" in each set, while the other 10 specimens were produced with a color difference level that increased gradually from BC. These stepped levels were obtained by controlled increasing of the pigment concentration in the relevant baseline silicon mixture. Color difference levels of specimens were calculated by using the CIELAB and CIEDE2000 formulas. Observers comprised of 3 different professional experiences as first-year dental students, interns, and dentists (n = 30/group, gender-balanced) were included. Combinations consisting of 5 specimens with 4 BCs and 1 different color were shown to the observers to assess whether the color difference was perceptible or acceptable. Perceptibility and acceptability percentages were regressed with color difference levels to estimate the best fit curve and confidence intervals were calculated (α = 0.05). The highest estimation of the coefficient of determination (R2) was found in the cubic curve for all parameters. A significant difference was found between the light and dark colors. The perceptibility thresholds (ΔE*ab/ΔE00) were 0.8/0.59 and 2.63/1.75 for light and dark colors, respectively. The acceptability thresholds (ΔE*ab/ΔE00) were 3.35/2.25, 10.07/7.04 for light and dark colors, respectively. No significant differences were found between gender and among experience groups concerning visual thresholds. Regardless of gender and experience, observers could perceive color differences more easily in light skin colors.