Predicted effectiveness of EnChroma multi-notch filters for enhancing color perception in anomalous trichromats.

EnChroma filters are aids designed to improve color vision for anomalous trichromats. Their use is controversial because the results of lab-based assessments of their effectiveness have so far largely failed to agree with positive anecdotal reports. However, the effectiveness of EnChroma filters will vary depending on the conditions of viewing, including whether the stimuli are broadband reflective surfaces or colors presented on RGB displays, whether illumination spectra are broadband or narrowband, the transmission spectra of particular filters, and the cone spectral sensitivity functions of the observer. We created a model of anomalous trichromatic color vision to predict the effects of EnChroma filters on the color signals impaired in anomalous trichromacy. Using the model we varied illumination, filter type and observer cone sensitivity functions, and tested the effect of presenting colors as broadband reflective surfaces or on RGB displays. We also used hyperspectral images to assess the impact of the filters on anomalous trichromats' color vision for natural scenes. Model results predicted that the filters should be broadly effective at enhancing anomalous trichromats' equivalent to L/(L + M) chromatic contrasts under a range of viewing conditions, but are substantially more effective for deuteranomals than for protanomals. The filters are predicted to be more effective for broadband reflective surfaces presented under broadband illuminants than for surfaces presented under narrowband illuminants or for colors presented on RGB displays. Since the potential impacts of contrast adaptation and perceptual learning are not considered in the model, it needs to be empirically validated. Results of empirical tests of the effects of EnChroma filters on deuteranomalous color vision in comparison with model predictions are presented in an accompanying paper (Somers et al., in prep.).

Empirical tests of the effectiveness of EnChroma multi-notch filters for enhancing color vision in deuteranomaly.

Manufacturers of notch filter-based aids for color vision claim that their products can enhance color perception for people with anomalous trichromacy, a form of color vision deficiency (CVD). Anecdotal reports imply that people with CVD can have radically enhanced color vision when using the filters. However, existing empirical research largely focussed on the effect of notch filters on performance on diagnostic tests for CVD has not found that they have any substantial effect. Informed by a model of anomalous trichromatic color vision, we selected stimuli predicted to reveal the effects of EnChroma filters. Using these stimuli, we tested the ability of EnChroma filters to enhance color vision for 10 deuteranomalous trichromats in three experiments: 1. asymmetric color matching between test and control filter conditions, 2. color discrimination measured using four alternative forced-choice, and 3. color appearance measured using dissimilarity ratings to reconstruct subjective color spaces using multidimensional scaling. To investigate potential effects of long-term adaptation or perceptual learning, participants completed all three experiments at two time points, on first exposure to the filters, and after a week of regular use. We found a significant effect of the filters on color matches in the direction predicted by the model at both time points, implying that the filters can enhance the anomalous trichromatic color gamut. However, we found minimal effect of the filters on color discrimination at threshold. We found a significant effect of the filters in enhancing the appearance of colors along the red-green axis at the first time point, and a trend in the same direction at the second time point. Our results provide the first quantitative experimental evidence that notch filters can enhance color perception for anomalous trichromats.

Difficult at dusk? Illuminating the debate on cricket ball visibility.

OBJECTIVES: Investigate the visibility of new and old red, white and pink cricket balls under lighting and background conditions experienced during a day-night cricket match. DESIGN: We modelled the luminance contrast signals available for a typical observer for a ball against backgrounds in a professional cricket ground, at different times of day. METHODS: Spectral reflectance (light reflected as a function of wavelength) was derived from laboratory measurements of new and old red, white and pink balls. We also gathered spectral measurements from backgrounds (pitch, grass, sightscreens, crowd, sky) and spectral illuminance during a day-night match (natural afternoon light, through dusk to night under floodlights) from Lord's Cricket Ground (London, UK). The luminance contrast of the ball relative to the background was calculated for each combination of ball, time of day, and background surface. RESULTS: Old red and old pink balls may offer little or no contrast against the grass, pitch and crowd. New pink balls can also be of low contrast against the crowd at dusk, as can pink and white balls (of any age) against the sky at dusk. CONCLUSIONS: Reports of difficulties with visibility of the pink ball are supported by our data. However, our modelling also shows that difficulties with visibility may also be expected under certain circumstances for red and white balls. The variable conditions in a cricket ground and the changing colour of an ageing ball make maintaining good visibility of the ball a challenge when playing day-night matches.

Chromatic and spatial image statistics predict infants' visual preferences and adults' aesthetic preferences for art.

Aesthetics has been characterized as a triadic interaction of perceptual, emotional, and conceptual neural systems (e.g., Chatterjee & Vartanian, 2014). There has been much empirical effort to identify the visual features that contribute to the perceptual component of this triad (e.g., Mather, 2020). Here, we measured infants' visual preferences and adults' aesthetic preferences for 40 of van Gogh's landscape paintings and investigated the contribution of the chromatic and spatial image statistics of the art to infants' and adults' responses. We found that infants' and adults' responses were significantly related: infants looked longer at the art that the adults found more pleasant. We also found that our combination of chromatic and spatial image statistics could account for around two thirds of the variance in infant looking and adult pleasantness ratings. The amount of variation in the luminance and saturation of the art's pixels contributed to both infants' visual preferences and adults' aesthetic preferences, potentially identifying two "perceptual primitives" of aesthetics that can be traced back to early sensory biases in infancy. We also identified important differences in the types of image statistics that predict infants' and adults' responses. We discuss the findings in relation to theories of aesthetics, natural scene statistics, and infant vision and perception.

Screening for mild anomalous trichromacy using the Ishihara plates test.

The Ishihara plates test is one of the most established and widely used means of identifying color vision deficiencies. However, literature examining the effectiveness of the Ishihara plates test has identified weaknesses, particularly when screening for milder anomalous trichromacy. We constructed a model of the chromatic signals expected to contribute to false negative readings by calculating, for particular anomalous trichromatic observers, the differences in chromaticity between the ground and pseudoisochromatic portions of plates. Predicted signals from five plates were compared for seven editions of the Ishihara plates test, for six observers with three severities of anomalous trichromacy, under eight illuminants. We found significant effects of variation in all of these factors other than edition on the predicted color signals available to read the plates. The impact of edition was tested behaviorally with 35 observers with color vision deficiency and 26 normal trichromats, which corroborated the minimal effect of edition predicted by the model. We found a significant negative relationship between predicted color signals for anomalous trichromats and behavioral false negative plate readings (ρ=-0.46, p=0.005 for deuteranomals, ρ=-0.42, p=0.01 for protanomals), suggesting that residual observer-specific color signals in portions of plates designed to be isochromatic may be contributing to false negative readings, and validating our modeling approach.

Colour vision is aligned with natural scene statistics at 4 months of age.

Visual perception in adult humans is thought to be tuned to represent the statistical regularities of natural scenes. For example, in adults, visual sensitivity to different hues shows an asymmetry which coincides with the statistical regularities of colour in the natural world. Infants are sensitive to statistical regularities in social and linguistic stimuli, but whether or not infants' visual systems are tuned to natural scene statistics is currently unclear. We measured colour discrimination in infants to investigate whether or not the visual system can represent chromatic scene statistics in very early life. Our results reveal the earliest association between vision and natural scene statistics that has yet been found: even as young as 4 months of age, colour vision is aligned with the distributions of colours in natural scenes. RESEARCH HIGHLIGHTS: We find infants' colour sensitivity is aligned with the distribution of colours in the natural world, as it is in adults. At just 4 months, infants' visual systems are tailored to extract and represent the statistical regularities of the natural world. This points to a drive for the human brain to represent statistical regularities even at a young age.

The effect of a short-wave filtering contact lens on color appearance.

We assessed the effect of a contact lens that filters short-wavelength (SW) visible light on color appearance. These effects were modeled and measured by direct comparison to a clear contact lens. Sixty-one subjects were enrolled, and 58 completed as cohort; 31 were 18 to 39 years old (mean ± SD, 29.6 ± 5.6), 27 were 40 to 65 years old (50.1 ± 8.1). A double-masked contralateral design was used; participants randomly wore a SW-filtering contact lens on one eye and a clear control lens on the other eye. Subjects then mixed three primaries (including a short-wave primary, strongly within the absorbance of the test lens) until a perceived perfect neutral white was achieved with each eye. Color appearance was quantified using chromaticity coordinates measured with a spectral radiometer within a custom-built tricolorimeter. Color vision in natural scenes was simulated using hyperspectral images and cone fundamentals based on a standard observer. Overall, the chromaticity coordinates of matches that were set using the SW-filtering contact lens (n = 58; x = 0.345, y = 0.325, u' = 0.222, v' = 0.470) and clear contact lens (n = 58; x = 0.344, y = 0.325, u' = 0.223, v' = 0.471) were not significantly different, regardless of age group. Simulations indicated that, for natural scenes, the SW-filtering contact lens that was evaluated changes L/(L+M) and S/(L+M) chromatic contrast by no more than -1.4% to +1.1% and -36.9% to +5.0%, respectively. Tricolorimetry was used to measure color appearance in subjects wearing a SW-filtering lens in one eye and a clear lens in the other, and the results indicate that imparting a subtle tint to a contact lens, as in the SW-filtering lens that was evaluated, does not alter color appearance for younger or older subjects. A model of color vision predicted little effect of the lens on chromatic contrast for natural scenes.

13q32.1 as a candidate region for physiological anisocoria.

BACKGROUND: Physiological anisocoria is an asymmetry of pupil size in the absence of pathology. METHODS: Images of the pupils under standard illumination were collected in the course of a whole-genome association study of a range of visual functions in 1060 healthy adults. DNA for each participant was extracted from saliva samples. RESULTS: We found no relationship between anisocoria and the difference in refraction between the eyes, nor between anisocoria and difference in acuity. There was a small but significant relationship with lightness of the iris, in that the eye with the smaller pupil was associated with the lighter iris. There was a strong association between anisocoria and a local region of chromosome 13 (13q32.1), a region lying between the genes GPR180 and SOX21. The strongest association was with the single-nucleotide polymorphism rs9524583. CONCLUSION: The very specific region associated with anisocoria is one where microdeletions (or microduplications) are known to lead to abnormal development of pupil dilator muscle and hence to the autosomal dominant condition of microcoria. It is possible that alterations at 13q32.1 act by altering the expression of SOX21, which encodes a nuclear transcription factor.

Nonlinear cortical encoding of color predicts enhanced McCollough effects in anomalous trichromats.

Nonlinear encoding of chromatic contrast by the early visual cortex predicts that anomalous trichromats will show a larger McCollough effect than normal trichromats. In Experiment 1 we employed the McCollough effect to probe the cortical representation of saturation in normal trichromats, and used the results to predict enhanced McCollough effects for anomalous trichromats, which we measured in Experiment 2. In Experiment 1 three participants adapted to red and green orthogonal gratings of four different saturations. Using nulling to measure aftereffect strength, we found that halving the saturation of the inducing gratings decreased aftereffect strength only slightly, consistent with a compressive coding of saturation in early visual cortex. In anomalous trichromats, cone contrasts between red and green are greatly decreased from those of normal trichromats, but induced aftereffects are only slightly decreased, because of the non-linearity in the cortical encoding of saturation. To null the aftereffect, however, the retinal color deficiency must be overcome by adding more color to the null than required by normal trichromats. We confirmed this prediction in Experiment 2 where four anomalous trichromats required nulling stimuli approximately four times more saturated than did normal trichromats. We consider two competing models to explain our results: in a 'pigment swap' model anomalous trichromats have an altered photopigment but process color postreceptorally in the same way as normal trichromats; in a 'postreceptoral compensation' model the cortical representation of red-green contrasts is amplified to compensate for reduced cone contrasts. The latter provided a better fit to our data.

Color-biased regions in the ventral visual pathway are food selective.

Color-biased regions have been found between face- and place-selective areas in the ventral visual pathway. To investigate the function of the color-biased regions in a pathway responsible for object recognition, we analyzed the natural scenes dataset (NSD), a large 7T fMRI dataset from 8 participants who each viewed up to 30,000 trials of images of colored natural scenes over more than 30 scanning sessions. In a whole-brain analysis, we correlated the average color saturation of the images with voxel responses, revealing color-biased regions that diverge into two streams, beginning in V4 and extending medially and laterally relative to the fusiform face area in both hemispheres. We drew regions of interest (ROIs) for the two streams and found that the images for each ROI that evoked the largest responses had certain characteristics: they contained food, circular objects, warmer hues, and had higher color saturation. Further analyses showed that food images were the strongest predictor of activity in these regions, implying the existence of medial and lateral ventral food streams (VFSs). We found that color also contributed independently to voxel responses, suggesting that the medial and lateral VFSs use both color and form to represent food. Our findings illustrate how high-resolution datasets such as the NSD can be used to disentangle the multifaceted contributions of many visual features to the neural representations of natural scenes.

Do You See What I See? Diversity in Human Color Perception.

In our tendency to discuss the objective properties of the external world, we may fail to notice that our subjective perceptions of those properties differ between individuals. Variability at all levels of the color vision system creates diversity in color perception, from discrimination to color matching, appearance, and subjective experience, such that each of us lives in a unique perceptual world. In this review, I discuss what is known about individual differences in color perception and its determinants, particularly considering genetically mediated variability in cone photopigments and the paradoxical effects of visual environments in both contributing to and counteracting individual differences. I make the case that, as well as being of interest in their own right and crucial for a complete account of color vision, individual differences can be used as a methodological tool in color science for the insights that they offer about the underlying mechanisms of perception.

Calibrating Vision: Concepts and Questions.

The idea that visual coding and perception are shaped by experience and adjust to changes in the environment or the observer is universally recognized as a cornerstone of visual processing, yet the functions and processes mediating these calibrations remain in many ways poorly understood. In this article we review a number of facets and issues surrounding the general notion of calibration, with a focus on plasticity within the encoding and representational stages of visual processing. These include how many types of calibrations there are - and how we decide; how plasticity for encoding is intertwined with other principles of sensory coding; how it is instantiated at the level of the dynamic networks mediating vision; how it varies with development or between individuals; and the factors that may limit the form or degree of the adjustments. Our goal is to give a small glimpse of an enormous and fundamental dimension of vision, and to point to some of the unresolved questions in our understanding of how and why ongoing calibrations are a pervasive and essential element of vision.

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.

Color discrimination in anomalous trichromacy: Experiment and theory.

In anomalous trichromacy, the color signals available from comparing the activities of the two classes of cone sensitive in the medium and long wavelength parts of the spectrum are much reduced from those available in normal trichromacy, and color discrimination thresholds along the red-green axis are correspondingly elevated. Yet there is evidence that suprathreshold color perception is relatively preserved; this has led to the suggestion that anomalous trichromats post-receptorally amplify their impoverished red-green signals. To test this idea, we measured chromatic discrimination from white and from saturated red and green pedestals. If there is no post-receptoral compensation, the anomalous trichromat's loss of chromatic contrast will apply equally to the pedestal and to the test color. Coupled with a compressively nonlinear neural representation of saturation, this means that a given pedestal contrast will cause a smaller than normal modulation of discrimination sensitivity. We examined cases where chromatic pedestals impair the color discrimination of normal trichromatic observers. As predicted, anomalous observers experienced less impairment than normal trichromats, though they remained less sensitive than normal trichromats. Although the effectiveness of chromatic pedestals in impairing color discrimination was less for anomalous than for normal trichromats, the chromatic pedestals were more effective for anomalous observers than would be expected if the anomalous post-receptoral visual system were the same as in normal trichromacy; the hypothesis of zero compensation can be rejected. This might suggest that the effective contrast of the pedestal is post-receptorally amplified. But on closer analysis, the results do not support candidate simple models involving post-receptoral compensation either.

Individual differences in the tendency to see the expected.

Prior knowledge has been shown to facilitate the incorporation of visual stimuli into awareness. We adopted an individual differences approach to explore whether a tendency to 'see the expected' is general or method-specific. We administered a binocular rivalry task and manipulated selective attention, as well as induced expectations via predictive context, self-generated imagery, expectancy cues, and perceptual priming. Most prior manipulations led to a facilitated awareness of the biased percept in binocular rivalry, whereas strong signal primes led to a suppressed awareness, i.e., adaptation. Correlations and factor analysis revealed that the facilitatory effect of priors on visual awareness is closely related to attentional control. We also investigated whether expectation-based biases predict perceptual abilities. Adaptation to strong primes predicted improved naturalistic change detection and the facilitatory effect of weak primes predicted the experience of perceptual anomalies. Taken together, our results indicate that the facilitatory effect of priors may be underpinned by an attentional mechanism but the tendency to 'see the expected' is method-specific.

Individual differences in change blindness are predicted by the strength and stability of visual representations.

The phenomenon of change blindness reveals that people are surprisingly poor at detecting unexpected visual changes; however, research on individual differences in detection ability is scarce. Predictive processing accounts of visual perception suggest that better change detection may be linked to assigning greater weight to prediction error signals, as indexed by an increased alternation rate in perceptual rivalry or greater sensitivity to low-level visual signals. Alternatively, superior detection ability may be associated with robust visual predictions against which sensory changes can be more effectively registered, suggesting an association with high-level mechanisms of visual short-term memory (VSTM) and attention. We administered a battery of 10 measures to explore these predictions and to determine, for the first time, the test-retest reliability of commonly used change detection measures. Change detection performance was stable over time and generalized from displays of static scenes to video clips. An exploratory factor analysis revealed two factors explaining performance across the battery, that we identify as visual stability (loading on change detection, attention measures, VSTM and perceptual rivalry) and visual ability (loading on iconic memory, temporal order judgments and contrast sensitivity). These results highlight the importance of strong, stable representations and the ability to resist distraction, in order to successfully incorporate unexpected changes into the contents of visual awareness.