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ROBERT SIEGEL, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.

MELISSA BLOCK, host:

And I'm Melissa Block.

3-D effects are everywhere these days: in movies, on TV, in video games. But the rush to 3-D may be hitting a bump in the road.

(Soundbite of video game, "Super Mario Brothers")

BLOCK: Nintendo is putting a warning label on its soon-to-be-released handheld game console. The company's website says the 3-D effects could cause vision problems in children under the age of 6. And other manufacturers have issued similar warnings. NPR's Joe Palca reports.

JOE PALCA: So how do you get a 3-D effect from a flat screen? Well, you do it by filming a scene with two cameras.

Ms. AHNA GIRSHICK (Vision Researcher, New York University): Each camera gets a slightly different view, and that creates what's called binocular disparity.

PALCA: That's Ahna Girshick. She's a vision researcher at New York University. Binocular disparity is what you get when you look at the world with two eyes. Each eye sends an image to the brain that sees the world from a slightly different angle.

Ms. GIRSHICK: The brain is accustomed to processing that. And it creates this 3-D impression.

PALCA: Makers of 3-D media are taking advantage of that.

Ms. GIRSHICK: So they're just piggybacking on this mechanism that's already built into our eyes and brains.

PALCA: But there's a problem: We also get some information about how far away an object is by how much we adjust the lens in our eyeball to bring it into focus.

Ms. GIRSHICK: So with a near display - like if you're looking at a TV and you are sitting up close - your eyes actually focus on the surface of the TV, and that's at one distance.

PALCA: But Girshick says if the TV is showing a 3-D image, your brain might think an object is far off in the distance, even though your focus is on the screen right in front of you.

Ms. GIRSHICK: And so these two systems are now in conflict. In the natural world, they're never in conflict.

PALCA: This artificially created conflict can cause eye fatigue and headache, and it's that artificial conflict that's causing some concerns about children using 3-D video games. Vision scientist David Hoffman works at the semiconductor company Mediatek. He says children's visual systems are changing as they grow.

Mr. DAVID HOFFMAN (Vision Scientist, Mediatek): Any time you've introduced something very different than what they're normally exposed to, there's a chance that they begin to adapt to whatever this new condition is.

PALCA: And that would be an unnatural condition that would possibly not be good for them when they weren't playing video games.

Mr. HOFFMAN: Right.

PALCA: There's not a lot of good data about just how much long-term damage these games could cause. They may cause no damage. But some game manufacturers have decided to err on the side of caution, and recommend that young children not use the 3-D mode. Of course, enforcing that recommendation falls to the parents.

Joe Palca, NPR News, Washington.

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