Mice See New Hue With Added Gene

Then the team tested the rodents' ability to discriminate among various colors, including thousands of trials focusing on the crucial green-red distinction. To make sure the animals were not simply noting a difference in brightness, they randomly made the red or green screens brighter.

Of five mice tested, three proved they could make use of their new cones, choosing correctly about 80 percent of the time. Only 33 percent would be expected by chance.

Why two of the mice failed remains unclear.

"Maybe they were just too dumb. Maybe they weren't motivated. One just doesn't know why, when an animal fails," Nathans said.

That three could immediately use the new information, however, proves that the brain is flexible enough to detail some of its neurons to handling new inputs, he said.

It is impossible to know how the enhanced mice are experiencing their spectrally enhanced world, Jacobs said -- whether the ordinary seems psychedelic and whether their quality of life is better.

"I don't know what you experience when you see colors," Jacobs said, "and I know even less about what the mouse is experiencing."

Indeed, some said, the fact that mice never acquired -- or at least never retained -- trichromatic vision suggests it may not be of much evolutionary value to them, perhaps because they are nocturnal.

By contrast, biologists theorize that the sudden ability to see red was a windfall for primates. Pink skin may signal good health in a prospective mate, a red face can warn of a rival's anger, and a lack of red can indicate fear -- a useful cue in a touch-and-go situation.

Jay Neitz, a vision scientist at the Medical College of Wisconsin in Milwaukee, said the work confirms his unpublished research in which he has cured red-green colorblindness in monkeys by injecting into their eyes the missing color-receptor gene. If further studies prove the approach is safe, he said, it could be used in people to correct colorblindness and perhaps to add a fourth color receptor, which would allow a finer parsing of the spectrum.

"You'd think that the color world of a tetrachromat would be very rich compared to ours," Neitz said.