How Seeing the New Color ‘Olo’ Opens the Realm of Vision Science

UC Berkeley scientists tricked the eye into seeing "the greenest green" they'd ever seen. They say it could transform how we understand and treat eye diseases, and expand the way we see the world around us.

Anyone who’s seen the original 1939 film The Wizard of Oz remembers the moment when Dorothy’s sepia-toned world turns to Technicolor. She steps out of her tornado-swept house into Munchkinland and takes in her new surroundings: A shiny yellow brick road winds through a miniature village of thatched-roof cottages and lush plants. She famously tells her trusty black terrier, “Toto, I have a feeling we’re not in Kansas anymore.”

A similar sense of awe, though grounded in science, recently unfolded at UC Berkeley. Using a technique aptly called Oz, scientists gave participants in a study the ability to see a brand new color — not in a faraway land, but right in their lab. 

Published in April, the study detailed how Berkeley researchers tricked the eye into seeing a highly saturated teal — a peacock green, the greenest of all greens. The scientists produced this color, which they named “olo,” by shining a laser into the eye and stimulating one type of color-sensitive photoreceptor cells called cones. 

The world was — and still is — very excited about this new discovery. Some who’ve heard about it have claimed that they, too, have seen the color. One artist is even selling an acrylic paint color for $10,000 that he claims gives users the experience of olo (it comes with a very steep coupon code). But unless they were in this lab at Berkeley, the only lab where it has happened, it’s not actually possible. That’s because the cones the researchers stimulated — the middle cones, or M cones, which are sensitive to green light — can’t be stimulated by themselves in a natural setting. 

This article was adapted from a Berkeley Voices podcast episode. Listen to the original episode here.

“There’s no light in nature that can only stimulate the M-cones,” said Austin Roorda, a professor of optometry and vision science at the School of Optometry at Berkeley. 

Roorda explained that the human eye has long, middle and short wavelength-sensitive cones called L, M and S cones. The M cones are sandwiched between the L and the S cones, so when the M cone is tickled, so are the L and the S. 

The study involved a team of researchers, including Ren Ng, a professor of electrical engineering and computer sciences at Berkeley. Their collaboration began years ago when Ng asked Roorda, “What would happen if we delivered light to thousands of M cones only? Would it be the greenest green you’ve ever seen?” 

Turns out, the answer was yes.

Ng and Roorda were two of five people who saw olo as part of the study. More have seen it since then, but time and logistics limited the number of subjects who could see it then. 

Roorda describes sitting perfectly still, gripping a bite plate between his teeth to keep his head from moving, staring into the Oz machine. The patch of color was about the size of his fingernail when viewed at arms’ length. When compared to the most saturated natural color of green next to it, Roorda said the natural green “paled in comparison.” 

It was exciting, he said, not only because their project had worked, but because the brain was able to recognize and make sense of something it had never been exposed to before.  

“It’s really about the capacity of the human brain to develop new perceptions to attribute to new sensory inputs,” said Roorda. “This could apply to any sensory inputs. It just turns out that we have a platform where we can directly manipulate the sensory inputs into the brain through the visual system in an unprecedented way.”

That has enormous potential to transform how we understand and treat eye diseases, Roorda said, and to expand the way we see the world around us.

A new dimension of color

It’s easy to assume that everyone sees the world as you do. And to be fair, most of us do, at least visually. The majority of people are trichromats, which means that we distinguish colors using three different types of photoreceptor cells in our retinas. With these three types of cone photoreceptors, we can appreciate up to 10 million different hues. 

“The human color vision system is really quite incredible,” said Roorda. “This Oz platform not only allows us to elicit color sensations that natural light would not, but we can use this as a tool to try to understand the basic processing of colors that humans perform when we’re looking at the world.”

Perception can be shaped, learned and developed through exposure, Roorda said. Children’s brains, for example, are especially open to taking in and making sense of new stimuli. “When you’re older, there may be a little less plasticity to do that,” said Roorda, “but we believe it’s there.”

As we age, our brains get a little more rigid in the ways they process what we’re seeing. But even still, what could seeing a new color do to the brain? Would it make it more flexible, more pliable, more receptive to new sensory phenomena? 

Roorda said there are two main theories: One is that you’re born with a box of crayons and those are the only colors you are able to perceive. If your eye saw a new color, it would reassign it to a color you already had in your selection. Another theory is that there is no limit to the percepts we have, or the different crayons we can collect. “We like to think that,” Roorda said. 

If the Berkeley researchers’ theory is true — that the human brain, this “wonderful machine,” as Roorda calls it, is powerful enough to decode colors it had never seen before — it could potentially open up a new dimension of experience. 

And research suggests that the human brain could, in fact, leverage this new information quite well.

One of the Oz project’s chief collaborators, Ph.D. student Atsu Kotani, is running simulations showing that a computer can easily figure out inputs from four cone types and then generate a new dimension of vision. “If a machine can do that, why couldn’t the human brain do that?” asked Roorda.  

There was also a 2009 study at the University of Washington that involved squirrel monkeys, which are dichromatic. Using gene therapy, the scientists gave the monkeys a third cone type. Afterward, the monkeys could differentiate between reddish and greenish tones, when they couldn’t before.

This type of gene therapy, although not available to humans right now, could be possible in the future, Roorda said. And Oz is one important tool to help us get there. 

The health benefits of Oz

There are many eye diseases where one’s cones are damaged or lose functionality over time, resulting in vision loss. Hannah Doyle, a fourth-year Ph.D. student in the Department of Electrical Engineering, ran the Oz experiment. She said there are many potential therapeutic applications of Oz. 

There are eye diseases that cause cones to die or to be lost in the retina, she explained, and people are interested in how those diseases affect visual function. Typically, scientists would have to find patients who have the disease, then do functional tests on their vision to figure out what stage of the disease they’re at. 

But with the Oz system, she said, the scientists can very easily emulate the conditions of these kinds of diseases. 

In the same way the researchers stimulated only the M cones for the eye to see olo, they can now use the imaging platform to stimulate a certain percentage of cones, mimicking the symptoms of cone loss of a given degenerative eye disease. 

This would allow doctors to better understand the experience of people with specific eye diseases and then treat them accordingly. 

“You could wonder, how would you do looking at an eye chart if you’ve lost 70% of your cones?” said Doyle. “Can you still read the letters? What’s the smallest letter you could read? It turns out that you can lose a lot of cones and still perform almost completely normally on an eye chart.” 

If you can give someone a better quality of life by maintaining their vision … this is really important for the individual, but also for the health benefit of the world. 

Austin Roorda, professor of optometry and vision science

If they find that a person can see well enough to, say, pass the vision portion of a driver’s test with 70% of their cones missing, added Roorda, scientists developing eye disease treatments using gene therapy or stem cell therapy will know that if they can restore cone densities to 30% of normal, the patients will have a high quality of life. “These are numbers that are very important in the area where there are treatments for any retinal disease coming online,” he said. 

There are huge personal costs of vision loss, said Roorda, and the benefits of preventing it are enormous. 

“I might be a little biased, but it’s our most precious sense,” he said. “It’s the last one I would want to give up, for sure. If you can give someone a better quality of life by maintaining their vision, whether it’s for reading or doing your hobbies or for driving, this is really important for the individual, but also for the health benefit of the world.” 

Like it did for Dorothy, Oz could impact the way we see our surroundings in dramatic ways that we can’t even imagine yet.