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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.

LDH: Funda??o de Amparo ? Pesquisa do Estado de S?o Paulo (FAPESP) post-doctoral fellowship 2019/14606-4 and Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) doctoral scholarship; EH: FAPESP post-doctoral fellowships 2014/25743-9 and 2018/09321-8; BSWC: Natural Sciences and Engineering Research Council (NSERC) Discovery grant; OFG: Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) Research Productivity Fellowship; PRKG: CNPq grant 484228/2011-0; DFV: FAPESP grant 2014/26818-2, CAPES ProAmazonia 3263/2013-19 and CNPq 309409/2015-2. Universidade de S?o Paulo. Instituto de Psicologia. Departamento de Psicologia Experimental. S?o Paulo, SP, Brazil. Universidade de S?o Paulo. Instituto de Psicologia. Departamento de Psicologia Experimental. S?o Paulo, SP, Brazil / Hospital Israelita Albert Einstein. Instituto de Ensino e Pesquisa. S?o Paulo, SP, Brazil. Universidade de S?o Paulo. Instituto de Psicologia. Departamento de Psicologia Experimental. S?o Paulo, SP, Brazil. University of Toronto. Department of Cell and System Biology. Toronto, Canada. Minist?rio da Sa?de. Secretaria de Vigil?ncia em Sa?de. Instituto Evandro Chagas. Centro Nacional de Primatas. Ananindeua, PA, Brasil. Universidade Federal do Par?. N?cleo de Medicina Tropical. Bel?m, PA, Brazil / Universidade Federal do Par?. Instituto de Ci?ncias Biol?gicas. Bel?m, PA, Brazil. Universidade Federal do Par?. N?cleo de Medicina Tropical. Bel?m, PA, Brazil / Universidade Federal do Par?. Instituto de Ci?ncias Biol?gicas. Bel?m, PA, Brazil. Universidade Federal do Par?. N?cleo de Teoria e Pesquisa do Comportamento. Bel?m, PA, Brazil Universidade Federal do Par?. N?cleo de Teoria e Pesquisa do Comportamento. Bel?m, PA, Brazil Universidade de S?o Paulo. Instituto de Psicologia. Departamento de Psicologia Experimental. S?o Paulo, SP, Brazil / Hospital Israelita Albert Einstein. Instituto de Ensino e Pesquisa. S?o Paulo, SP, Brazil. Primate colour vision depends on a matrix of photoreceptors, a neuronal post receptoral structure and a combination of genes that culminate in different sensitivity through the visual spectrum. Along with a common cone opsin gene for short wavelengths (sws1), Neotropical primates (Platyrrhini) have only one cone opsin gene for medium-long wavelengths (mws/lws) per X chromosome while Paleotropical primates (Catarrhini), including humans, have two active genes. Therefore, while female platyrrhines may be trichromats, males are always dichromats. The genus Alouatta is inferred to be an exception to this rule, as electrophysiological, behavioural and molecular analyses indicated a potential for male trichromacy in this genus. However, it is very important to ascertain by a combination of genetic and behavioural analyses whether this potential translates in terms of colour discrimination capability. We evaluated two howler monkeys (Alouatta spp.), one male A. caraya and one female A. seniculus, using a combination of genetic analysis of the opsin gene sequences and a behavioral colour discrimination test not previously used in this genus. Both individuals completed the behavioural test with performances typical of trichromatic colour vision and the genetic analysis of the swsl, mws, and Iws opsin genes revealed three different opsin sequences in both subjects. These results are consistent with uniform trichromacy in both male and female, with presumed spectral sensitivity peaks similar to Catarrhini, at similar to 430 nm, 532 nm, and 563 nm for S-, M- and L-cones, respectively.

Albinism is a rare phenotype that affects the pigmentation in eyes, hair, and skin. The effects of albinism in color vision are still unclear. Our study aimed to evaluate the color vision phenotype and genotype of an albino capuchin monkey. An adult albino male capuchin monkey (Sapajus apella) had the L and M opsin gene analyzed, and was trained in a behavioral task of color discrimination. Color discrimination thresholds were determined along 20 chromatic axes around the background chromaticity. A color discrimination ellipse was drawn by interpolation among these thresholds. The albino monkey’s behavioral color discrimination ellipse showed poor discrimination along the red–green axis indicating a deutan phenotype. Genetic analysis revealed only the presence of the L gene in the albino monkey. This result did not differ from that obtained with ten previously tested non-albino monkeys. Behavioral and molecular analyses agreed that the albino capuchin monkey had color vision similar to that of non-albino dichromat monkeys, suggesting no influence of albinism on color discrimination.

We investigated the impact of visual impairment on balance control. We measured the center of pressure (COP) between the two feet and plantar surface pressures on each foot in 18 normal-sighted participants and compared their data with measures from 18 legally blind participants, either acquired or congenital. Pressures were measured in open- and closed-eye conditions using a baropodometric resistive plate. In the eyes-open condition, there were no differences between the sighted and legally blind groups in COP displacement. However, participants with visual loss had significantly increased pressures in two metatarsal regions (M1 and M2 zones) of the plantar surface in both viewing conditions (p < 0.05). The differences in pressure measures between the normally sighted and legally blind groups could be attributed mainly to the subgroup of subjects with acquired impairment. Our findings suggest that subjects with visual impairment present increased metatarsal pressures (i.e. forefoot), not yet associated to anterior displacement of COP or impaired balance control.

The identification of color vision types in primates is fundamental to understanding the evolution and biological function of color perception. The Hard, Randy, and Rittler (HRR) pseudoisochromatic test categorizes human color vision types successfully. Here we provide an experimental setup to employ HRR in a nonhuman primate, the capuchin (Cebus libidinosus), a platyrrhine with polymorphic color vision. The HRR test consists of plates with a matrix composed of gray circles that vary in size and brightness. Differently colored circles form a geometric shape (X, O, or Δ) that is discriminated visually from the gray background pattern. The ability to identify these shapes determines the type of dyschromatopsy (deficiency in color vision). We tested six capuchins in their own cages under natural sunlight. The subjects chose between two HRR plates in each trial: one with the gray pattern only and the other with a colored shape, presented on the left or right side at random. We presented the test 40 times and calculated the 95 % confidence limits for chance performance based on the binomial test. We also genotyped all subjects for exons 3 and 5 of the X-linked opsin genes. The HRR test diagnosed two subjects as protan dichromats (missing or defective L-cone), three as deutan dichromats (missing or defective M-cone), and one female as trichromat. Genetic analysis supported the behavioral data for all subjects. These findings show that the HRR test can be applied to diagnose color vision in nonhuman primates.