Austin Roorda of UC Berkeley was one of the researchers who saw the new super-saturated color using the Oz platform. [Image: Austin Roorda]
Researchers at the University of California, Berkeley, USA, have shown that the human eye can be manipulated to see a completely new color that they have dubbed “olo” (Sci. Adv., doi: 10.1126/sciadv.adu1052) Described as a blue-green shade of unparalleled saturation, olo can only be perceived with a platform that uses weak pulses of green laser light to individually control up to 1,000 photoreceptors in the eye at the same time.
“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,” says coauthor James Carl Fong. “It gives us a way to study the human retina at a new scale that has never been possible in practice”
Cones of color vision
Color vision in humans is generated by three types of “cone” cells within the retina: S cones detect blue wavelengths, M cones detect green and L cones detect red. However, the spectral response of the M cones entirely overlaps with those of the S and L cones, which means that no wavelength of light can stimulate the M cones on their own.
To see the color generated by only the M cones, the researchers turned to a technology that was recently developed to help ophthalmologists study eye disease. This technique exploits microdoses of green laser light to target and activate one or two photoreceptors on the retina. To create a whole new visual experience, however, the researchers needed a system that could selectively stimulate thousands of photoreceptors at the same time.
Participants in the study described olo as blue-green or peacock green, but much more saturated than other monochromatic colors.
Reaching the Emerald City
Their platform, which they call “Oz,” works by scanning a laser beam over a small patch of the retina, delivering tiny pulses of light when the beam reaches a cone that the system has been programmed to activate. Precise targeting is achieved by first mapping out the positions of the three different cone cells on each subject’s retina and then by tracking the natural movement of the eye in real time using an infrared imaging system.
The system can be programmed to stimulate a combination of S, M and L cone cells to produce full-color images, or to activate only the M cone cells to reveal the new hue in both image and video formats. Participants in the study described olo as blue-green or peacock green, but much more saturated than other monochromatic colors. When the laser was directed slightly off target, causing the light pulses to activate other types of cone cells nearby, the participants immediately stopped seeing olo and saw only the normal green light of the laser.
The team believe that the programmable platform could offer new insights into human vision and eye disease. Many types of visual impairment involve the loss of cone cells, and the novel technique could enable researchers to simulate that experience among healthy subjects. It could also enable scientists to probe more fundamental questions about how the brain responds to new sensory inputs, which could offer a way to improve the visual experience for people who are color blind.