This shows a rainbow.
Patterson says improving our understanding of the retina’s complex processes could ultimately help lead to better methods for restoring vision for people who have lost it. Credit: Neuroscience News

Decoding the Rainbow: New Secrets of Color Perception

Summary: Researchers made significant progress in understanding color perception by identifying non-cardinal retinal ganglion cells (RGCs) in the human fovea. These cells may explain complex color perceptions beyond the traditional models established by the cardinal directions of color detection.

Utilizing adaptive optics, the team overcame challenges posed by the eye’s natural aberrations to study these elusive cells. Their findings could lead to advanced vision restoration techniques and enhance retinal prosthetic designs.

Key Facts:

  1. Adaptive optics technology, initially developed for astronomy, was pivotal in allowing researchers to clearly image individual retinal cells, revealing the detailed structure and function of rare non-cardinal RGCs.
  2. The study challenges existing theories of color perception, which are based on three types of cone photoreceptors and the cardinal directions of color detection, by suggesting a role for non-cardinal RGCs in creating more nuanced color perception.
  3. The research received support from prestigious institutions, including the National Institutes of Health and the Air Force Office of Scientific Research, underscoring its significance and potential impact on vision science.

Source: University of Rochester

Scientists have long wondered how the eye’s three cone photoreceptor types work together to allow humans to perceive color.

In a new study in the Journal of Neuroscience, researchers at the University of Rochester used adaptive optics to identify rare retinal ganglion cells (RGCs) that could help fill in the gaps in existing theories of color perception.

The retina has three types of cones to detect color that are sensitive to either short, medium, or long wavelengths of light. Retinal ganglion cells transmit input from these cones to the central nervous system.

In the 1980s, David Williams, the William G. Allyn Professor of Medical Optics, helped map the “cardinal directions” that explain color detection.

However, there are differences in the way the eye detects color and how color appears to humans. Scientists suspected that while most RGCs follow the cardinal directions, they may work in tandem with small numbers of non-cardinal RGCs to create more complex perceptions.

Recently, a team of researchers from Rochester’s Center for Visual Science, the Institute of Optics, and the Flaum Eye Institute identified some of these elusive non-cardinal RGCs in the fovea that could explain how humans see red, green, blue, and yellow.

“We don’t really know anything for certain yet about these cells other than that they exist,” says Sara Patterson, a postdoctoral researcher at the Center for Visual Science who led the study.

“There’s so much more that we have to learn about how their response properties operate, but they’re a compelling option as a missing link in how our retina processes color.”

Using adaptive optics to overcome light distortion in the eye

The team leveraged adaptive optics, which uses a deformable mirror to overcome light distortion and was first developed by astronomers to reduce image blur in ground-based telescopes.

In the 1990s, Williams and his colleagues began applying adaptive optics to study the human eye. They created a camera that compensated for distortions caused by the eye’s natural aberrations, producing a clear image of individual photoreceptor cells.

“The optics of the eye’s lens are imperfect and really reduce the amount of resolution you can get with an ophthalmoscope,” says Patterson.

“Adaptive optics detects and corrects for these aberrations and gives us a crystal-clear look into the eye. This gives us unprecedented access to the retinal ganglion cells, which are the sole source of visual information to the brain.”

Patterson says improving our understanding of the retina’s complex processes could ultimately help lead to better methods for restoring vision for people who have lost it.

“Humans have more than 20 ganglion cells and our models of human vision are only based on three,” says Patterson.

“There’s so much going on in the retina that we don’t know about. This is one of the rare areas where engineering has totally outpaced visual basic science.

“People are out there with retinal prosthetics in their eyes right now, but if we knew what all those cells do, we could actually have retinal prosthetics drive ganglion cells in accordance with their actual functional roles.”

Funding: The work was supported through funding by the National Institutes of Health, Air Force Office of Scientific Research, and Research to Prevent Blindness.

About this color perception and visual neuroscience research news

Author: Luke Auburn
Source: University of Rochester
Contact: Luke Auburn – University of Rochester
Image: The image is credited to Neuroscience News

Original Research: Closed access.
Cone-Opponent Ganglion Cells in the Primate Fovea Tuned to Non-Cardinal Color Directions” by Sara Patterson et al. Journal of Neuroscience


Cone-Opponent Ganglion Cells in the Primate Fovea Tuned to Non-Cardinal Color Directions

A long-standing question in vision science is how the three cone photoreceptor types – long (L), medium (M) and short (S) wavelength sensitive – combine to generate our perception of color. Hue perception can be described along two opponent axes: red-green and blue-yellow.

Psychophysical measurements of color appearance indicate that the cone inputs to the red-green and blue-yellow opponent axes are M vs. L+S and L vs. M+S, respectively.

However, the “cardinal directions of color space” revealed by psychophysical measurements of color detection thresholds following adaptation are L vs. M and S vs. L+M.

These cardinal directions match the most common cone-opponent retinal ganglion cells (RGCs) in the primate retina. Accordingly, the cone opponency necessary for color appearance is thought to be established in cortex.

However, small populations with the appropriate M vs. L+S and L vs. M+S cone-opponency have been reported in large surveys of cone inputs to primate RGCs and their projections to the lateral geniculate nucleus (LGN), yet their existence continues to be debated.

Resolving this long-standing open question is necessary because a complete account of the cone-opponency in the retinal output is critical for efforts to understand how downstream neural circuits process color.

Here, we performed adaptive optics calcium imaging to longitudinally, noninvasively measure foveal RGC light responses in the living macaque (Macaca fascicularis) eye.

We confirm the presence of L vs. M+S and M vs. L+S neurons with non-cardinal cone-opponency and demonstrate that cone-opponent signals in the retinal output are more diverse than classically thought.

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