The clear, bright yellow of a lemon is a far cry from the flat, waxy color of butter or the soft gold of champagne. But we recognize them all as yellow.
Is that because our visual brain categorizes the continuous spectrum of colors into groups? Or is it our language that determines how we perceive colors? After all, Isaac Newton's breakup of the visible spectrum included a blue-purple color called indigo. But indigo was later stripped of its status as a color. Isaac Asimov wrote in the 1970s, "It has never seemed to me that indigo is worth the dignity of being considered a separate color. To my eyes it seems merely deep blue."
To find out how we categorize so many different hues into groups of yellow, orange, green and so on, scientists turned to babies, who, unlike Newton and Asimov, are not yet influenced by language. As reported Monday in Proceedings of the National Academy of Sciences, it turns out that color categories might be clear to us long before we have the words for them.
"Color categories seem to be defined, to our surprise, before (or independent of) the acquisition of language," said coauthor Jiale Yang, a psychologist at Chuo University in Tokyo, in an email to Brain Decoder.
Humans can discern thousands of colors, at a conservative estimate. And we have many names for them, from magenta to saffron to cerulean to chartreuse. But each language breaks colors into only a few basic categories. These can range from 11 to 12 terms in most languages spoken in industrialized cultures to as few as two in others. English and Japanese have eleven: black, white, gray, pink, brown, red, orange, yellow, green, blue and purple.
To see whether these categories can develop before language and which brain areas encode them, Yang and his colleagues scanned the brains of both adults and infants ages 5 to 7 months. Using NIRS, a technique that is similar to fMRI but easier to use on babies, the team monitored activity in areas involved in color processing.
In one experiment, participants saw a grid of shapes that flashed between two different colors. When watching colors switch from blue to green, adults and babies had a spike in activity in a region called the occipito-temporal cortex, which is involved in visual processing. When the colors alternated between different shades of green, there was no boost. This suggested that different color categories are recognized in the visual cortex in infants.
To confirm that babies use similar categories to adults, the team did a second experiment. First they showed infants a smiling face pattern in one color. The babies then saw that face alongside a second one, identical save for its color. Sometimes the faces were two shades of green, sometimes two shades of blue and sometimes one was blue and the other green. In each pair, the two hues used were equally distant from each other on the color spectrum.
The researchers wanted to see how long the babies would spend looking at the new-color face. Babies are interested in novelty and usually look at new stimuli longer than old ones, so if they stared longer at that face, it would mean they recognized it as being different enough to merit further investigation. The babies spent significantly longer looking at the new face only when it belonged in a different color category from the one they'd first been shown.
And while babies showed they were aware of the difference between color categories, we also know they are likely able to distinguish color variations within each category. One line of evidence comes from a previous experiment, in which babies could find a green target on a background that was a different shade of green.
The new findings suggest that the ability to perceive different color categories might have an innate foundation across languages and cultures, the researchers concluded. But this doesn't mean we all group our colors the same way.
"The effect of language pressure for inter-personal communication…may modify the sensory categories later," Yang said. "The color categories we perceive are corresponding to the color lexicons we use, and more importantly, they may be different across languages."
In other words, Newton and Asimov's virtual debate on the existence of indigo is not yet solved. In fact, the color blue is particularly contested across cultures. Unlike English, the Russian language has different words for lighter blues (goluboy) and darker blues (siniy). For a Russian speaker, goluboy and siniy are as distinct from each other as yellow is from green.
"There is no single generic word for 'blue' in Russian that can be used to…adequately translate the title of this work from English to Russian," the authors of a 2007 paper called "Russian blues reveal effects of language on color discrimination" noted cheekily.
In their experiment, native English and Russian speakers had to quickly distinguish various shades of blue. Russian speakers were faster, compared with English speakers, in discriminating goluboy and siniy.
"The critical difference in this case is not that English speakers cannot distinguish between light and dark blues, but rather that Russian speakers cannot avoid distinguishing them: they must do so to speak Russian in a conventional manner," the researchers wrote. "The case of the Russian blues suggests that habitual or obligatory categorical distinctions made in one's language result in language-specific categorical distortions in objective perceptual tasks."
So we might start with a few universal color distinctions. But the ways they are fine-tuned by our language do end up affecting our perception.
Image: Jiale Yang, Chuo University