Color Perception Is Not In The Eye Of The Beholder: It's In The Brain
First-ever images of living human retinas have yielded a surprise about how we perceive our world. Researchers at the University of Rochester have found that the number of color-sensitive cones in the human retina differs dramatically among people—by up to 40 times—yet people appear to perceive colors the same way. The findings, on the cover of this week's journal Neuroscience, strongly suggest that our perception of color is controlled much more by our brains than by our eyes."We were able to precisely image and count the color-receptive cones in a living human eye for the first time, and we were astonished at the results," says David Williams, Allyn Professor of Medical Optics and director of the Center for Visual Science. "We've shown that color perception goes far beyond the hardware of the eye, and that leads to a lot of interesting questions about how and why we perceive color."
Williams and his research team, led by postdoctoral student Heidi Hofer, now an assistant professor at the University of Houston, used a laser-based system developed by Williams that maps out the topography of the inner eye in exquisite detail. The technology, known as adaptive optics, was originally used by astronomers in telescopes to compensate for the blurring of starlight caused by the atmosphere.
Williams turned the technique from the heavens back toward the eye to compensate for common aberrations. The technique allows researchers to study the living retina in ways that were never before possible. The pigment that allows each cone in the human eye to react to different colors is very fragile and normal microscope light bleaches it away. This means that looking at the retina from a cadaver yields almost no information on the arrangement of their cones, and there is certainly no ability to test for color perception. Likewise, the amino acids that make up two of the three different-colored cones are so similar that there are no stains that can bind to some and not others, a process often used by researchers to differentiate cell types under a microscope.
This, the researchers say, may explain why young children who have had a large portion of one side of the brain surgically removed often recover completely. "This knowledge may give new hope for rehabilitation of brain function in adults after stroke or traumatic brain injuries," said Dr. Szaflarski. "The fact that language adaptability is seen even in the older people supports the notion that these patients can be rehabilitated and returned to productive life, possibly even after a devastating stroke." Scientists have long thought that the hemisphere or side of the brain that controls language and speech is determined before birth. Most people are right-handed and demonstrate more activity during language or speech in the left hemisphere of the brain. In left-handed people language centers are located more symmetrically. Drs. Szaflarski and Holland studied brain activity in 177 right-handed children and adults aged 5 to 67 at Cincinnati's University Hospital and Cincinnati Children's using functional magnetic resonance imaging (fMRI). The technique shows brain activity, in this case language tasks such as reading or speaking, in a specific color. 
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