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Color Perception Is Not in the Eye of the Beholder


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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.

 

lefthttp://hypography.com/gallery/files/9/9/8/retina_thumb.jpg[/img]"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.

 

Imaging the living retina allowed Williams to shine light directly into the eye to see what wavelengths each cone reflects and absorbs, and thus to which color each is responsive. In addition, the technique allows scientists to image more than a thousand cones at once, giving an unprecedented look at the composition and distribution of color cones in the eyes of living humans with varied retinal structure.

 

Each subject was asked to tune the color of a disk of light to produce a pure yellow light that was neither reddish yellow nor greenish yellow. Everyone selected nearly the same wavelength of yellow, showing an obvious consensus over what color they perceived yellow to be. Once Williams looked into their eyes, however, he was surprised to see that the number of long- and middle-wavelength cones - the cones that detect red, green, and yellow - were sometimes profusely scattered throughout the retina, and sometimes barely evident. The discrepancy was more than a 40:1 ratio, yet all the volunteers were apparently seeing the same color yellow.

 

"Those early experiments showed that everyone we tested has the same color experience despite this really profound difference in the front-end of their visual system," says Hofer. "That points to some kind of normalization or auto-calibration mechanism - some kind of circuit in the brain that balances the colors for you no matter what the hardware is."

 

In a related experiment, Williams and a postdoctoral fellow Yasuki Yamauchi, working with other collaborators from the Medical College of Wisconsin, gave several people colored contacts to wear for four hours a day. While wearing the contacts, people tended to eventually feel as if they were not wearing the contacts, just as people who wear colored sunglasses tend to see colors "correctly" after a few minutes with the sunglasses. The volunteers' normal color vision, however, began to shift after several weeks of contact use. Even when not wearing the contacts, they all began to select a pure yellow that was a different wavelength than they had before wearing the contacts.

 

"Over time, we were able to shift their natural perception of yellow in one direction, and then the other," says Williams. "This is direct evidence for an internal, automatic calibrator of color perception. These experiments show that color is defined by our experience in the world, and since we all share the same world, we arrive at the same definition of colors."

 

Williams' team is now looking to identify the genetic basis for this large variation between retinas. Early tests on the original volunteers showed no simple connection among certain genes and the number and diversity of color cones, but Williams is continuing to search for the responsible combination of genes.

 

Source: University of Rochester

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It's not only color perception :

 

Michael Brady quote :

http://www.physlink.com/Education/AskExperts/ae353.cfm

"It is true that the images formed on your retina are upside-down. It is also true that most people have two eyes, and therefore two retinas. Why, then, don't you see two distinct images? For the same reason that you don't see everything upside-down. One of our most remarkable tools - the brain - is hard at work for us at this task."

 

But how does the brain do that ?? What's physical detail explaination ?

We have 'myopic eye','color-blind' but why we don't have genetic case of "inverted-eye".

 

Another experts with their quotes :

 

Paul Doherty with his pin and hole :

http://www.exo.net/~pauld/summer_institute/summer_day3eye_and_brain/pin_and__hole.html

What's Going On?

Your cornea and lens makes an inverted and right-to-left reversed image on your retina.

Your brain inverts the image.

You perceive the image to be uninverted and unreversed.

 

Donald E Simanek with his adding depth to illusions:

http://www.lhup.edu/~dsimanek/3d/illus2.htm

 

My quote :

What makes inverted and reversed images of the illusions ?

If electron-microscopy apply magnetic-field lens, is there something like "gravity-field mirror/lens" in our mind ? Just speculation.

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What makes inverted and reversed images of the illusions ?

 

Which illusions? BTW the image is corrected in the cornea, or the optical nerve that goes from the eye to the brain.

 

If electron-microscopy apply magnetic-field lens, is there something like "gravity-field mirror/lens" in our mind ? Just speculation.

 

Not likely. Even in zero gravity, astronauts see correctly. The reversion of the retina image is a necessary function for our sense of perception.

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Fascinating article! I've always wondered if people perceive colour in the same way. For example, if what I call "blue" looked more like my idea of "green" to someone else. Well, this study seems to indicate that we all see the same thing after all.

 

Since we're on the topic of colour, what do you think of the reasons (psychological, sociological, etc.) for liking/disliking certain colours? For example, my favourite colour fluctuates between blue and green - does this indicate a personality change or a mood change? And does my intense hate of the colour orange really mean something?

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I tested the illusion site also. I got the rotating green, and all the pink disappeared. I even refocussed onto an edge and was able to see a circle of green dots as well as the pink at the same time. Then I tried moving very close to my monitor, with my nose only a few inches from the screen, and focussing just on the + in the center. All of the dots except the one rotating green disappeared, and i actually saw a grey colored box. I actually repeated this three times, just to be sure. There really was a grey box. Very cool stuff.

Thanks for the link, oh master of news articles!

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