Researchers at the University of California, Berkeley have developed a method that allows people to see a new color, named “olo,” by using a laser-based technique called Oz. The study, published in April, involved stimulating only the M cones—photoreceptor cells in the eye sensitive to green light—something not possible under natural conditions.
Austin Roorda, professor of optometry and vision science at UC Berkeley, explained that natural light cannot selectively stimulate just the M cones. “There’s no light in nature that can only stimulate the M-cones,” said Roorda. He described how the human eye contains three types of cones: L (long), M (middle), and S (short) wavelength-sensitive cones. Typically, when one type is stimulated, so are its neighbors.
The idea for this research began years ago when Ren Ng, professor of electrical engineering and computer sciences at Berkeley, asked Roorda what would happen if thousands of M cones were stimulated alone. Their experiment confirmed that this produced an extremely saturated shade of green unlike any seen before.
Ng and Roorda were among five initial participants who saw olo during the study. Roorda described his experience with the Oz machine as striking: “When compared to the most saturated natural color of green next to it,” he said, “the natural green ‘paled in comparison.’” He added that their work demonstrates “the capacity of the human brain to develop new perceptions to attribute to new sensory inputs.”
Roorda emphasized broader implications for vision science: “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.” He noted potential applications for understanding and treating eye diseases.
Most people are trichromats—able to distinguish colors using three types of cone photoreceptors—and can perceive up to 10 million hues. According to Roorda: “The human color vision system is really quite incredible. 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.”
The research team also included Atsu Kotani, Ph.D. student at UC Berkeley, who is running simulations indicating computers can process input from four cone types and generate additional dimensions of vision perception. Roorda questioned whether humans might similarly adapt if given new types of visual input.
Previous studies support this possibility; for example, researchers at University of Washington used gene therapy on squirrel monkeys—who naturally lack certain cone types—to give them trichromatic vision previously unavailable to them.
Hannah Doyle, fourth-year Ph.D. student in electrical engineering at UC Berkeley who ran many Oz experiments, highlighted therapeutic uses for simulating degenerative eye disease conditions by selectively stimulating specific percentages of cones in healthy subjects’ eyes. This approach could help doctors better understand patient experiences with retinal diseases and inform treatment strategies.
“You could wonder, how would you do looking at an eye chart if you’ve lost 70% of your cones?” said Doyle. She found that significant cone loss does not always result in severe impairment on standard tests like reading an eye chart.
Roorda noted these findings are important for developing therapies such as gene or stem cell treatments: If patients retain even 30% normal cone density after treatment they may still enjoy high quality vision suitable for daily life activities including driving.
“I might be a little biased,” said Roorda about sight’s importance,“but it’s our most precious sense… 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.”
