Industry News
Researchers Unveil Tech That Creates Colours Beyond Human Vision
According to new research, a groundbreaking new principle for displaying colour, dubbed 'Oz', could fundamentally change visual technology by directly stimulating individual photoreceptor cells in the human retina. The technique, demonstrated in a proof-of-principle prototype, not only reproduces conventional colours using a single light source but has successfully generated colours previously impossible for humans to perceive, effectively expanding the known boundaries of our colour vision.
Developed by a research team utilising advanced optical techniques, the Oz system bypasses traditional methods of colour reproduction, like those used in RGB screens or CMYK printing, which rely on mixing spectral light sources ('spectral metamerism'). Instead, Oz employs what the researchers term 'spatial metamerism' – precisely controlling the spatial distribution of light at a microscopic level on the retina itself.
The core technology hinges on Adaptive Optics Scanning Light Ophthalmoscopy (AOSLO). This allows the system to perform two critical functions simultaneously:
- Real-time Retinal Imaging: Using near-invisible infrared light, the AOSLO system tracks the eye's constant, minute fixational movements at cellular scale (up to 960 Hz for processing).
- Targeted Stimulation: Based on the eye tracking, the system delivers incredibly precise 'microdoses' of visible-wavelength laser light (e.g., 488nm or 543nm) directly to targeted individual cone cells (L, M, or S types) at a rate exceeding 100,000 microdoses per second across thousands of cells.
"This technical achievement introduces an experimental platform for visual perception with a new class of precision, programmable control, and cellular scale," the research paper states.
To achieve this, the system requires a pre-existing map of the subject's retina, detailing each cone cell's location and spectral type (L, M, or S) within the target area, obtained using AO-OCT techniques. During operation, the system calculates which cones need to be activated, and how intensely, to reproduce a desired image or colour percept as it moves across the retina due to natural eye drift.
The most significant demonstration is the creation of colours outside the natural human gamut. In normal vision, the spectral sensitivities of the three cone types (L, M, S) overlap. Activating Medium-wavelength (M) cones inevitably co-activates neighbouring L and/or S cones.
The Oz system, however, can theoretically target light only to M cones. While perfect isolation wasn't achieved in practice (researchers estimate about one-third of light hit the target cone, two-thirds leaked to neighbours), it was precise enough to produce a perceptual effect never before experienced.
Researchers named this novel M-cone-only stimulation 'olo'. Human subjects participating in rigorous colour-matching experiments described 'olo' (generated using a 543nm green laser) as an "unprecedentedly saturated" blue-green or teal colour. Critically, subjects found they had to add white light to 'olo' to match it to the most saturated possible monochromatic teal light (around 501-512nm) that exists on the boundary of the normal human colour gamut. This need to desaturate 'olo' provides "unequivocal proof that olo lies beyond the gamut," according to the study.
Further experiments confirmed subjects could perceive images and videos rendered using Oz colours, such as identifying the orientation of a red line or the rotation of a red dot presented on an 'olo' background. When the system's precision was deliberately compromised (by 'jittering' the laser targeting), subjects' performance dropped to chance levels, highlighting the necessity of accurate cone-by-cone stimulation.
The current prototype is limited to a small 0.9° field of view at 4° eccentricity and requires subjects to maintain fixation. Scaling the technology to larger, free-gaze systems presents substantial hurdles: mapping millions of cones across wider retinal areas (including the densely packed fovea), achieving near-perfect optical focus and microdose targeting accuracy during rapid eye movements (saccades), and massive increases in computational power and data bandwidth.
Despite these challenges, Oz represents a potentially revolutionary tool for vision science and neuroscience. "Oz represents a new class of experimental platform... which strives for complete control of the first neural layer to the brain," the researchers note.
Potential future research directions include:
- Probing the fundamental mechanisms of colour perception and retinal processing.
- Investigating visual phenomena and retinal diseases at a cellular level.
- Exploring neural plasticity – for example, simulating the signals of a missing cone type in colourblind individuals or even attempting to induce tetrachromatic (four-colour) perception in trichromats.
While direct commercial display applications are distant, the underlying principles of spatial metamerism could influence future developments in specialised visual technologies, augmented reality, or therapeutic visual aids. The ability to program visual input at the photoreceptor level opens a new frontier in understanding and potentially manipulating human sight.
The research is published at https://www.science.org/doi/10.1126/sciadv.adu1052
