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Five people have seen a color never before visible to the naked human eye, thanks to a new retinal stimulation technique called Oz. In a proof-of-concept experiment, Oz overcame the retina’s natural limits, activating thousands of retinal cone cells to reveal a highly saturated blue-green color. “Oz represents a new class of experimental platform for vision science and neuroscience, which strives for complete control of the first neural layer to the brain,” James Fongand colleagues write. Today’s color reproduction techniques manipulate light spectra to activate retinal cone cells. However, these cells overlap in their response to select wavelengths and intensities, limiting which colors humans can see. Now, James Fongand colleagues have developed a way to overcome this limitation. Their approach centers around spatial metamerism, which controls the spatial distribution of light on the retina rather than the spectra of light itself. Analyses of retinal cells showed that this strategy, called Oz, affects photoreceptor behavior and enables selective induction of M cone cell activity. Fong et al. built an Oz laser system that delivered light from cell to cell in 5 people. This process triggered M cone cell activity leading people to see color described as “blue-green of unprecedented saturation.” Oz also produced this color in videos and images viewed by the participants. The authors suggest their Oz approach could one day be used to improve color vision in those with colorblindness.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Dr Misha Corobyew, Senior Lecturer, Optometry and Vision Science
We have three spectral types of cone photoreceptors (S, M and L for short-, middle and long- wavelength) with overlapping spectral sensitivities. Due to this overlap, any spectral light excites at least two spectral types of cones simultaneously. This limits the saturation of colours that we see. The paper uses a technique that allows to excite a single cone by shining a focussed laser light on it. This method of cone stimulation produces colours that do not exist in nature. When only M cone is stimulated, observers report that they see an unusually saturated greenish blue. Normally, focussed on retina point source, such as a star, excites several cones due optical constraints. To overcome this, adaptive optics is used, a method that astronomists use to look at stars. Single cone stimulation was known earlier. The novelty of this paper is that they use this method to stimulate many individual cones and produce an image.
