Mind & Body

How Do Blind People Think About Color?

When you think about a given "thing," chances are it comes in one of three forms: a concrete object (like a cup or a planet), a concept you can sense (like a color), or an abstract concept that you can't perceive with your senses (like fairness or love). Neuroscience studies have found that each of these concepts tends to activate different parts of a single region of the brain. But what about a person born blind who's never seen color? Does the brain of a blind person process the concept of color differently than a sighted person? A new study found out.

Animal, Vegetable, Conceptual

The study, which was co-authored by Harvard University's Alfonso Caramazza and published in the journal Nature Communications in December, didn't just set out to determine how blind people think about color. Rather, it was designed to clear up science's muddy understanding of how the brain actually processes different types of information.

In previous research, scientists have scanned people's brains while they thought about concrete and abstract concepts. They've found that the two activate many different parts of the brain, with language centers lighting up in response to abstract words, for instance, and sensory centers activating with concrete concepts. Still, there's one region of the brain that seems to do most of the heavy lifting: the left anterior temporal lobe, or ATL (if you make a fist with your right hand to represent the left side of the brain, this area would be around your thumb).

But, as we mentioned at the top of the article, the world isn't just made of concrete concepts you can sense and abstract concepts you can't. What about things you can see but not touch, like "red"? Or things that you can't perceive with your senses but still trigger an emotion, like "love"? It's hard to simply point to which areas of the ATL are activated by these words because there's so much context that could come to the participants' minds and skew the results. The best way to find out which parts of the ATL activate in response to each of these concepts would be to remove a variable — like the sense of sight — and see how differently the brain responds.

Do You See What I See?

That's exactly what the researchers did. They put 14 sighted people and 12 people who had been blind at birth into a brain scanner, then recited words to them. Some of those words were concrete, everyday objects, like "cup"; some were abstract, non-sensory concepts like "freedom"; and some were concepts that could only be conceived visually, like "rainbow" and "red."

It turned out that while the blind and sighted participants processed concrete and abstract concepts in the same brain regions (concrete concepts activated the medial ATL; purely abstract concepts activated the dorsolateral ATL), there were differences when it came to purely visual concepts. While sighted people processed a concept like "red" in the anterior ATL, blind people processed it in the dorsolateral ATL — the same part of the brain where they processed purely abstract concepts.

"We found that, in the congenitally blind, the neural responses for red were in the same areas as the neural responses for justice," Caramazza said in a press release. "The abstractness of something like red in the blind is the same as the abstractness of virtue for the sighted, and in both cases that information is represented in a part of the brain where information is obtained through linguistic processes."

What the study couldn't determine was exactly how a blind person experiences color as a concept, but that, Caramazza says, is for philosophers to figure out. Studies show that people born blind are actually really good at describing color, to the point where they can even arrange colors in a color wheel in their spectral sequence, with purple next to blue and red next to orange, etc. Just because a blind person understands color as an abstract concept doesn't mean that they don't truly understand it.

"You could be talking to a blind person, and if you didn't know they were blind, you would never suspect that their experience of red is different from yours, because in fact they do know what red means," Caramazza said. "They know what it means in the same way you come to know what justice means."

This study emphasizes the idea that even if we all perceive the world in slightly different ways, we can come to a similar understanding. Unless it's The Dress; then all bets are off.

Get stories like this one in your inbox or your headphones: Sign up for our daily email and subscribe to the Curiosity Daily podcast.

Find out more about how people see the world in "Vision: A Computational Investigation into the Human Representation and Processing of Visual Information" by David Marr. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer April 30, 2019

Curiosity uses cookies to improve site performance, for analytics and for advertising. By continuing to use our site, you accept our use of cookies, our Privacy Policy and Terms of Use.