Where is the color of what we see? Is it part of the object we see? Is it in the light from that object? Is it in our eyes, our retinas? Or is it in the brain?
All of the above, I believe, are where there is formation of what is ultimately termed a color, in many of the different senses of the term color, including color wavelength, color sensation and their many subtypes. Optical
illusions can show us that there is more to color vision than light alone.
Perhaps, the retina in particular is where a particular color (not just its wavelengths) actually begins to become what we can see. The article below shows that selective stimulation of a population of cone cells in a way that is not offset by nearby cells not activated by the computer-controlled micro-laser can create a color that they report is noticeably different from any prior color sensation. The color still seems to fit in a color wheel in its shade (turquoise green) if not in its saturation.
This seems to work because our eyes have 3 cone cell types, and the light wavelengths for a given frequency tend to stimulate more than one type, for example unavoidably in usual function stimulating L cone cells with similar wavelengths as green-sensing M cone cells (see the graph of cell stimulation versus wavelength from Wikipedia below):
The ingenuity of the creators of this study's equipment is commendable, as that equipment allowed them to bypass the usual limitations of the eye's SML color scheme.
It's also clear that those who see this color have learned what a previously unknown shade of green looks like. This amounts to a kind of scientific confirmation of
Frank Jackson's knowledge argument.
----------------------------------------------------------------------------
ABSTRACT
AU - James Fong
AU - Hannah K. Doyle
AU - Congli Wang
AU - Alexandra E. Boehm
AU - Sofie R. Herbeck
AU - Vimal Prabhu Pandiyan
AU - Brian P. Schmidt
AU - Pavan Tiruveedhula
AU - John E. Vanston
AU - William S. Tuten
AU - Ramkumar Sabesan
AU - Austin Roorda
AU - Ren Ng
TI - Novel color via stimulation of individual photoreceptors at population scale
PT - Journal Article
DP - 2025
TA - Science Advances
PG - eadu1052
VI - 11
IP - 16
AID - 10.1126/sciadv.adu1052 [doi]
PMID - 40249825
4099 - https://www.science.org/doi/abs/10.1126/sciadv.adu1052
4100 - https://www.science.org/doi/full/10.1126/sciadv.adu1052
SO - Science Advances 2025-04-18 11(16): eadu1052
AB - We introduce a principle, Oz, for displaying color imagery: directly controlling the human eye’s
photoreceptor activity via cell-by-cell light delivery. Theoretically, novel colors are possible through
bypassing the constraints set by the cone spectral sensitivities and activating M cone cells exclusively.
In practice, we confirm a partial expansion of colorspace toward that theoretical ideal. Attempting to
activate M cones exclusively is shown to elicit a color beyond the natural human gamut, formally measured
with color matching by human subjects. They describe the color as blue-green of unprecedented saturation.
Further experiments show that subjects perceive Oz colors in image and video form. The prototype targets
laser microdoses to thousands of spectrally classified cones under fixational eye motion. These results
are proof-of-principle for programmable control over individual photoreceptors at population scale.
Image display by cell-by-cell retina stimulation, enabling colors impossible to see under natural viewing.
