OK, I got this.

That's really hard.

[beep] OK, I got this.

I don't got this.

[beep] Try catching with one eye closed.

It's hard.

In fact, some athletes practice catching with one eye closed because it's so unfamiliar.

OK, this time with both eyes.

Piece of cake.

Besides being accustomed to it, you have a kind of super vision when you use two eyes, 3D vision.

Each eye sees a different image of the world, and that stereoscopic vision allows you to see bi-ocular, binocular, parallax.

Have you ever noticed that, when you close one eye, your right eye would say that your finger is to the left of the camera, but your left eye would say it's to the right?

What?

Your brain is smarter than that.

It uses these two images to triangulate the position of your finger in 3D space.

Unless it's broken.

Some people do not have stereoscopic vision.

They don't see 3D when they look with two eyes.

Stereoscopic processing in your brain is developed during early childhood.

And for a while, it was thought that if you didn't develop this ability by a certain age-- for example, if you had a lazy eye or were cross-eyed-- you would only be able to focus one eye at a time.

You would always just see 2D flat images, and your brain would never learn stereoscopy.

But in 2012, Bruce Bridgeman, a neuroscientist at UC Santa Cruz who had never had stereoscopic vision, went to see the movie "Hugo" in 3D.

As he told the BBC, he didn't expect anything special.

But as he watched the movie, the 3D images jumped out at him.

The movie forced his eyes to see two images individually, and his brain was able to process them together.

From then on it was like a switch, and he saw the rest of the world with stereoscopic vision.

It's a world that I take for granted.

But when you close one eye, you realize how much it's like looking at a flat screen.

Well, right now you are looking at a flat screen.

Binocular parallax is the only depth perception cue your eyes give you, besides shading and familiarity with objects.

Unless you move.

Your brain has another trick to see 3D, and it's called motion parallax.

Motion parallax is when the background you're looking at appears to move only about this much, while the foreground moves this much.

Which is probably why Cyclops wobbles so much.

"Hugo" and other 3D movies offer you binocular parallax.

They're shot on two cameras side by side, like our eyes.

Then at the theater, both images are projected onto the screen.

And those super sweet glasses they give you often use a polarizing filter to send the correct image to the corresponding eye.

Now what about glasses-less 3D TVs?

How do those work?

Any technology offering binocular parallax has to send two different images to your two eyes.

Some glasses-less 3D TVs do this by alternating strips of the two images with a barrier in between so that the correct image goes to the corresponding eye.

But the problem with this technology is that you have to see it dead on.

If you move even a little bit to the left or right, the 3D effect is lost.

Now how true is this 3D, or the 3D in movie theaters?

Try moving your head side to side in a theater and you'll notice that the image doesn't change.

Unless the camera was moving while filming, 3D movies don't have motion parallax.

That's because the camera shot from one fixed position.

Is there any technology that offers true 3D?

Yes.

Holograms.

Holograms are incredible photographic feats that allow you to see 3D images.

They've got the parallax effect, the depth perception, they have it all.

I'm here at the MIT Museum, where they have a new set of holograms opening in a new exhibit.

I wish you could be here with me, though, because there's nothing like seeing a hologram in person.

I kid you not.

This is coming from a two-dimensional hologram.

This film is flat.

I see the depth perception because of the two different images that my eyes are seeing.

I see the parallax effect because of the fact that the parts in the background, like the certificate on the wall, move less than the parts in the foreground of the hologram, like the pen.

Just a reminder.

These are real holograms.

This is not.

The obvious flaw with holograms is that they must often be illuminated with one color of light, which is achieved by shining a laser on the film from behind.

So they're not true colored.

But they are nonetheless impressive, beautiful, and truly 3D views from a 2D medium.

So what about holographic video?

Well, researchers from MIT managed to make holographic video reenactments of Princess Leia.

It was just in one wavelength in red light, but hopefully it's a step toward truly holographic films.

Here's to the future of 3D.

[music playing]