(Photo by Trevor McKinnon/Unsplash)A new hue
UC Berkeley researchers have found a way to manipulate the human eye into seeing a brand-new color — a blue-green color of unparalleled saturation that the research team has named “olo.”
Their technique, called “Oz,” works by focusing tiny doses of laser light to individually control up to 1,000 photoreceptors in the eye at one time. Using Oz, the team can show people not only a blue-green more stunning than anything in nature, but also other colors, lines, moving dots and images of babies and fish.
“We’ve created a system that can track, target and stimulate photoreceptor cells with such high precision that we can now answer very basic, but also very thought-provoking, questions about the nature of human color vision,” said James Carl Fong, Ph.D. student in electrical engineering and computer sciences (EECS). “It gives us a way to study the human retina at a new scale that has never been possible in practice.”
Humans can see in color thanks to three types of photoreceptor “cone” cells embedded in the retina: S cones detect shorter, bluer wavelengths; M cones detect medium, greenish wavelengths; and L cones detect longer, reddish wavelengths. However, the light wavelengths that activate the M and L cones are almost entirely overlapping. This means that 85% of the light that activates M cones also activates L cones.
“There’s no wavelength in the world that can stimulate only the M cone,” said Ren Ng, professor of EECS, “I began wondering what it would look like if you could just stimulate all the M cone cells. Would it be like the greenest green you’ve ever seen?”
To find out, Ng teamed up with Austin Roorda, professor of optometry and vision science, who had created a technology that used tiny microdoses of laser light to target and activate individual photoreceptors. But for Oz to work, researchers needed a map of the unique arrangement of the S, M and L cone cells on an individual’s retina. For this, the researchers collaborated with Ramkumar Sabesan and Vimal Prahbhu Pandiyan at the University of Washington, who have developed an optical system that can image the human retina and identify each cone cell.
With an individual’s cone map in hand, the Oz system can be programmed to rapidly scan a laser beam over a small patch of the retina, delivering tiny pulses of energy when the beam reaches a cone that it wants to activate, and otherwise staying off. The laser beam is just one color — the same hue as a green laser pointer — but by activating a combination of S, M and L cone cells, it can trick the eye into seeing images in a range of hues. Or, by primarily activating the M cone cells, Oz can show people the color olo.
Hannah Doyle, Ph.D. student in EECS, designed and ran the experiments with Oz. When participants compared olo to other colors, they described it as blue-green or peacock green and reported that it was much more saturated than the nearest monochromatic color. Doyle also tried “jittering” the Oz laser, directing it ever-so-slightly off target so the light pulses hit random cones rather than only M cones. The participants immediately stopped seeing olo and started seeing the regular green of the laser.
The research team is already finding ways to use the technique to study eye disease and vision loss caused by lost cone cells. They are also exploring whether Oz could help people with color blindness or allow humans to see in tetrachromatic color.
UC Berkeley’s Congli Wang, Alexandra Boehm, Sophie Herbeck, Brian Schmidt, Pavan Tiruveedhula, John Vanston and William Tuten also contributed to the study.
Learn more: Scientists trick the eye into seeing new color ‘olo’ (Berkeley News); Novel color via stimulation of individual photoreceptors at population scale (Science Advances)