In this article we present data comparing red–green dichromats' use of “Basic Color Terms” (BCTs) with that of standard trichromats. In a complementary article (Color Res Appl 2013) we use these data to evaluate two models of the mechanisms underlying dichromats' use of BCTs. There were three groups of observers—trichromats, protanopes, and deuteranopes—that each performed two tasks: “mapping” (which of these are exemplars of X?) and “best exemplar” (which is the best instance of X?), where X took the value of each Spanish BCT. The mapping task results were subjected to multidimensional scaling that revealed that dichromats differ from trichromats in the number and nature of the dimensions needed for describing BCTs' use. Trichromats required three dimensions closely related to the opponent color mechanisms (red–green, yellow–blue) and the light‐dark channel. In contrast, tridimensional solution for dichromats was difficult to interpret, whereas the fit for the bidimensional solution was very good and revealed a chromatic dimension, which did not match any of the trichromatic dimensions, and an achromatic one. There were also some error‐asymmetries (sometimes “A” was the predominant error when choosing exemplars of “B”, but not vice versa) and the groups differed in the frequency of use of some BCTs (e.g., protanopes chose more stimuli as orange than trichromats and deuteranopes). As expected, the best exemplar task produced more correct responses than the mapping task, and for both tasks, “primary” BCTs (black, white, red, green, yellow, and blue) produced better results than “derived” ones (brown, purple, orange, pink, and grey). © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 360–371, 2014

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.dichromacy | aesthetic preference | color vision | color naming I ndividuals vary in their perceptual experience of the world, and sometimes this variation is caused by genetic differences (1-4). Dichromacy is a form of color-vision deficiency affecting about 2% of human males in which only two of the three types of retinal cone photoreceptors are functional because of genetic factors (1, 2). Protanopes, deuteranopes, and tritanopes lack cone photoreceptors sensitive to long (L), medium (M), and short (S) wavelengths, respectively. Accordingly, dichromats' color discrimination is poorer, and their spectral sensitivity is slightly shifted to longer wavelengths (deuteranopes) or is moderately shifted to shorter wavelengths (protanopes) compared with that of normal trichromats (common observers; see table 3.6 in ref. 5).In normal trichromats, cone responses are the input signals for two chromatic cone opponent mechanisms, red-green and yellowblue, based on L−M and S−(L+M) cone responses, respectively, and one achromatic mechanism, mainly based on L+M responses (1). Traditionally it has been considered that protanopes and deuteranopes lack functionality in the red-green mechanism, because this opponent mechanism is based on the comparison of L and M cone responses, and one...

In our companion article (Color Res Appl 2013) we compared the use of Basic Color Terms (BCTs) by normal trichromats, protanopes, and deuteranopes in a mapping (which colors are instances of X?) and best exemplar (which is the best X?) tasks. In this article, we describe and compare two alternative models of the mechanisms underlying the use of Basic Color Terms (BCTs) by red–green dichromats and we focus on how well they fit the empirical data described in the companion article. Model A assumes that BCT use is based on the activity of the yellow–blue and lightness channels, whereas Model B also assumes that there is some degree of input from the red–green channel. Model B was more accurate than Model A in predicting: (1) The frequency of use of BCTs. (2) The distribution of correct responses for many BCTs in both tasks. (3) The distribution of correct responses and kind of errors for many BCTs. (4) The locations of the centroids for both tasks. We conclude that activity in a“residual” red–green channel influences the use of BCTs by R‐G dichromats, as well as the activity of the yellow–blue and lightness channels. The asymmetry of errors for some pairs of BCTs and the differences between primary and derived BCTs are also discussed. This article, in combination with its complementary one (Color Res Appl 2013), provides a comprehensive and detailed overview of how R‐G dichromats use BCTs to categorize surface colors and can integrate and explain some of the results and conclusions obtained in earlier research. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 372–386, 2014

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.

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