Julio Lillo

Color preference in red–green dichromats

Significance Around 2% of males have red–green dichromacy, which is a genetic disorder of color vision that affects how well certain colors can be seen and discriminated. Humans with normal color vision are known to have systematic and reliable preferences for some colors over others (e.g., blue is liked and yellow-green is disliked). We show that red–green dichromats have a different reliable pattern of color preference in which, for example, yellow is the most, not the least, preferred color. We test current theories of color preference and provide novel evidence that how easily a color can be named is related to how much it is liked. The findings further understanding of dichromacy, color preference, and aesthetics in general. 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.

An experimental method for the assessment of color simulation tools

The Simulcheck method for evaluating the accuracy of color simulation tools in relation to dichromats is described and used to test three color simulation tools: Variantor, Coblis, and Vischeck. A total of 10 dichromats (five protanopes, five deuteranopes) and 10 normal trichromats participated in the current study. Simulcheck includes two psychophysical tasks: the Pseudoachromatic Stimuli Identification task and the Minimum Achromatic Contrast task. The Pseudoachromatic Stimuli Identification task allows determination of the two chromatic angles (h(uv) values) that generate a minimum response in the yellow–blue opponent mechanism and, consequently, pseudoachromatic stimuli (greens or reds). The Minimum Achromatic Contrast task requires the selection of the gray background that produces minimum contrast (near zero change in the achromatic mechanism) for each pseudoachromatic stimulus selected in the previous task (L(R) values). Results showed important differences in the colorimetric transformations performed by the three evaluated simulation tools and their accuracy levels. Vischeck simulation accurately implemented the algorithm of Brettel, Viénot, and Mollon (1997). Only Vischeck appeared accurate (similarity in huv and L(R) values between real and simulated dichromats) and, consequently, could render reliable color selections. It is concluded that Simulcheck is a consistent method because it provided an equivalent pattern of results for huv and L(R) values irrespective of the stimulus set used to evaluate a simulation tool. Simulcheck was also considered valid because real dichromats provided expected huv and LR values when performing the two psychophysical tasks included in this method.

Blocking with serial compound stimuli: The role of local context and second-order associations

Blocking was studied with rats in two serial conditioning experiments in which CS1 was followed by CS2 and then shock. Experiment 1 demonstrated that pretraining with CS1 was able to block conditioning to CS2 when the pretraining consisted of trace conditioning. But when serial conditioning was used for pretraining, with a third stimulus as the second element of the compound, then blocking was not detected during the subsequent phase. In Experiment 2 the effect of pretraining with CS2 on blocking with CS1 was examined. Blocking was effective, but only when steps were taken to minimize the growth of second-order associations resulting from the pairing of CS1 with CS2. These results are consistent with a principle stating that the ability of a pretrained stimulus to block the added stimulus in a compound depends on the relative contiguity of each stimulus to the US.

Robust colour constancy in red-green dichromats

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.

Lighting and work: Light for seeing and healthy light

Abstract A critical analysis was performed of legislation regarding lighting conditions in working environments. It is shown that the Royal Decree 486/1997 uses a version of the traditional approach to lighting design as conceptual framework, in which: (1) Only the effects of light related to visual system performance are considered. (2) The quantitative effects associated with changes in type of lighting (different coloured lights) are ignored. A review was carried out of the aspects of lighting which should be taken into consideration to complement those included in the traditional approach. These aspects were: (1) Differentiation between photometric and apparent illumination. (2) The type (colour temperature) and quality (colour rendering index) of illumination. (3) The effects of lighting on the health of workers owing to its influence on the functioning of the circadian system.