Scientists Say: Stereoscopy

Stereoscopy tricks the brain into seeing a set of 2-D images as a 3-D scene

two girls wearing VR headsets and holding handheld controllers sit on the floor and smile as they play a video game

Stereoscopy allows our brains to see sets of 2-D images, such as those displayed on the inside of virtual reality, or VR, goggles, as portraying a 3-D scene.

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Stereoscopy (noun, “Stair-ee-AH-skuh-pee”)

Stereoscopy is a technique to trick the brain into perceiving flat images as three-dimensional scenes. Here’s how it works. Each eye is shown a picture of a flat, or two-dimensional, scene. The two pictures are almost identical but show the scene from slightly different angles. When viewing that pair of 2-D pictures together, the brain interprets them as a 3-D scene.

This mimics what the brain does in the real, 3-D world we live in. In everyday life, each of your eyes can perceive only a flat image of what’s in front of you. And because your eyes are separated by a small distance, they each see the world from slightly different angles. (To see this difference, close one eye and then the other. Watch how the objects in front of you appear to shift a tiny bit.)

The brain combines the visual input from each eye. In the process, the brain uses the slight differences between those two 2-D images to work out the distances to various objects within the field of view. (Say, for instance, you’re looking at a pencil sitting on your desk. Your eyes get two slightly different 2-D views of that pencil. By comparing those two flat images, your brain can estimate how far away the pencil is.) This is called depth perception. And it works whether your eyes are taking in two slightly different views of the real, 3-D world — or two versions of a 2-D scene displayed on a screen.

This effect is behind much of today’s immersive tech. Virtual reality headsets show slightly different images to each eye to make on-screen images feel real. Stereoscopy has also been used to make 3-D movies. In these films, right-eye and left-eye images are both displayed on screen. Special glasses help show the correct image to each eye. Old-school 3-D glasses did this by letting each eye see only specific colors of light. More sophisticated glasses now show each eye only light waves that wiggle at specific angles. Either way, the brain can assemble the 2-D view through each lens into an image that leaps off the screen.

In a sentence

Stereoscopy tricks the brain into thinking the flat images displayed on virtual reality headsets are 3-D scenes.

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Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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