Stimulating the retina to allow people to see a brand new color

A team of engineers, computer scientists and ophthalmologists at the University of California, Berkeley, working with a pair of colleagues at the University of Washington, has developed a technique for stimulating the retina that allows people to see a color not normally seen by humans.

In their study published in the journal Science Advances, the group identified certain photoreceptors in volunteers and then stimulated them to allow those volunteers to see the unique color, which the team has named "olo."

The human eye has two types of photoreceptors, rods and cones. Rods are used mostly to see in dark conditions. Cones are further divided into long, medium and short cones (L, M and S) depending on which wavelength of light they process most efficiently. Prior research has shown that there is some overlap in light processing between the cones, and the researchers wondered what would happen if light were only processed by one type, such as M.

To find out, they used adaptive optics optical coherence tomography to identify the M photoreceptors in a section of the retina for several volunteers—such maps are unique for each person. They then had each volunteer take turns sitting in front of a small square target and focusing on a certain part of it while a laser was fired at the M photoreceptors. The researchers call their technique Oz, an homage to the "Wizard of Oz" books.

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The volunteers, which included some of the researchers themselves, were able to see a color the team calls olo, after the letters that correspond to numbers 0, 1 and 0, representing the L, M or S photoreceptors. Most described it as a highly saturated blue-green. The research team then showed the volunteers photographs and videos with the olo color added, allowing for a novel viewing experience.

The team suggests their technique might be a useful way to study color blindness and perhaps even to treat the disorder by simulating the experience of stimulating a fourth type of cone—one that occurs naturally in some people with tetrachromacy.

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