Colour-space distortion in women who are heterozygous for colour deficiency

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. Expected final online publication date for the Annual Review of Vision Science, Volume 8 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Is the Helmholtz–Kohlrausch Effect More Robust in Women?

For gray or achromatic objects, brightness is a relatively simple transformation where very low luminance levels are perceived as black and higher levels are perceived as white. For chromatic objects, the transformation is more complex, depending on color purity as well. This influence of color purity on a color’s perceived brightness is a well-established phenomenon known as the Helmholtz–Kohlrausch (H-K) effect. We investigated gender differences in the H-K effect by measuring brightness (via direct brightness matching [DBM]) and luminance (via heterochromatic flicker photometry [HFP]) at five wavelengths (450, 520, 560, 580, and 650 nm) perceived as blue, green, green-yellow, yellow, and red hues. We compared DBM/HFP ratios between 13 males and 18 females. Based on previous evidence of a female advantage in chromatic processes, we hypothesized that DBM/HFP ratios would be higher in female subjects. While HFP measures were essentially the same between male and female subjects, DBM measures and DBM/HFP ratios were significantly higher for female subjects than males. There were no significant effects of contraceptive use based on a post hoc comparison. We also derived simple models of brightness as a function of luminance and saturation, which further suggest gender dimorphism in the H-K effect.

Color Perception in Protanomalous Female Macaca fascicularis

Protanomalous females with X chromosome-linked color vision deficiency exhibit mild abnormalities, whereas dichromats show a distinct deficiency in discriminating certain color pairs. Dichromats have an advantage in detecting a textured target when it is camouflaged by red-green colors, owing to their insensitivity to these colors. However, it is not certain whether protanomalous females possess a similar advantage in breaking camouflage. Here, we introduce an animal model of dichromatic macaque monkeys and protanomalous females. We examined whether protanomalous females have the same advantage in breaking color camouflage as shown by dichromatic macaques. We also tested whether they could discriminate a certain color pair that trichromats could, where the dichromats are confused. Our experiments show that protanomalous macaques can break color camouflage, similar to dichromats, and can discriminate colors similarly to trichromats. Protanomalous females are thus thought to have the combined ecological advantages of being both trichromats and dichromats.

Perceptual color spacing derived from maximum likelihood multidimensional scaling

The canonical application of multidimensional scaling (MDS) methods has been to color dissimilarities, visualizing these as distances in a low-dimensional space. Some questions remain: How well can the locations of stimuli in color space be recovered when data are sparse, and how well can systematic individual variations in perceptual scaling be distinguished from stochastic noise? We collected triadic comparisons for saturated and desaturated sets of Natural Color System samples, each set forming an approximate hue circle. Maximum likelihood MDS was used to reconstruct the configuration of stimuli more accurately than the standard "vote-count" approach. Individual departures from the consensus response pattern were minor, but repeated across stimulus sets, and identifiable as variations in the salience of color-space axes. No gender differences could be discerned, contrary to earlier results.

Colour vision in ADHD: part 1--testing the retinal dopaminergic hypothesis

OBJECTIVES

To test the retinal dopaminergic hypothesis, which posits deficient blue color perception in ADHD, resulting from hypofunctioning CNS and retinal dopamine, to which blue cones are exquisitely sensitive. Also, purported sex differences in red color perception were explored.

METHODS

30 young adults diagnosed with ADHD and 30 healthy young adults, matched on age and gender, performed a psychophysical task to measure blue and red color saturation and contrast discrimination ability. Visual function measures, such as the Visual Activities Questionnaire (VAQ) and Farnsworth-Munsell 100 hue test (FMT), were also administered.

RESULTS

Females with ADHD were less accurate in discriminating blue and red color saturation relative to controls but did not differ in contrast sensitivity. Female control participants were better at discriminating red saturation than males, but no sex difference was present within the ADHD group.

CONCLUSION

Poorer discrimination of red as well as blue color saturation in the female ADHD group may be partly attributable to a hypo-dopaminergic state in the retina, given that color perception (blue-yellow and red-green) is based on input from S-cones (short wavelength cone system) early in the visual pathway. The origin of female superiority in red perception may be rooted in sex-specific functional specialization in hunter-gather societies. The absence of this sexual dimorphism for red colour perception in ADHD females warrants further investigation.

The chromatic parameters of isoluminant chromatic motion examined with dissimilarity judgements

A moving edge or contrast between equiluminant colours produces a weaker motion percept than that defined by luminance contrast. However, the specific contrasts that determine chromatic motion have not been explored systematically. Here, rivalrous chromatic motion displays were produced by superimposing two gratings, one drifting from left to right and the other in the opposite direction. Each grating oscillated between equiluminant endpoints chosen from a pool of 16 colours. The rivalrous ambiguity resolved spontaneously for each display as the more-dissimilar colour pair dominated the less-dissimilar pair, and produced a percept of motion in the corresponding direction. These dissimilarity judgements were analysed with multidimensional scaling to represent 'motion salience' as distances in a colour map, to gauge whether chromatic motion is enhanced or weakened if the oscillation aligns with particular directions in the colour plane. Judgements were compared with other control judgements involving standard subjective dissimilarities between the same stimuli. Notably, chromatic motion was strongest when grating endpoints were separated along an orange-blue direction. This does not coincide with either cardinal axis of cone space, (L-M) or S(0) , but rather is a direction that would arise if motion is computed from a combination of the (L-M) and S(0) signals.

Flicker between equal-luminance colors examined with multidimensional scaling

Even when two rapidly alternating color stimuli are equated in luminance, the flicker between them is not always zero. By one hypothesis this residual chromatic flicker is tritanopic, like edge distinctness: dependent purely on L- and M-cone stimulation, with no contribution from S-cones. Judgments of flicker intensity between pairs of colors were analyzed with multidimensional scaling (MDS)--in effect treating them as an index of color dissimilarity. They reveal a systematic reduction of flicker when stimulus pairs differ along a chartreuse-magenta direction in the color plane, corresponding to an effective compression of color space along this axis or an equivalent elongation along a blue-orange axis. In contrast, judgments of edge distinctness between the same pairs reveal the expected tritanopic axis of compression. It follows that chromatic flicker does receive a contribution from S-cone stimulation, but this interacts with the contribution from L- and M-cones, perhaps due to phase delays.

Evolutionary models of color categorization. II. Realistic observer models and population heterogeneity

The evolution of color categorization is investigated using computer simulations of agent population categorization games. Various realistic observer types are implemented based on Farnsworth-Munsell 100 Hue Test human performance data from normal and anomalous trichromats, dichromats, and humans with four retinal photopigments. Results show that (i) a small percentage of realistically modeled deficient agents greatly affects the shared categorization solutions of the entire population in terms of color category boundary locations; (ii) for realistically modeled populations, dichromats have the strongest influence on the color categorization; their characteristic forms of color confusion affect (i.e., attract or repel) color boundary locations and accord with our findings for homogeneous dichromat populations [J. Opt. Soc. Am. A26, 1414-1423 (2009)]; (iii) adding anomalous trichromats or trichromat "experts" does not destabilize the solutions or substantially alter solution structure. The results provide insights regarding the mechanisms that may constrain universal tendencies in human color categorization systems.