Most people with normal binocular vision are capable of seeing the depth in autostereograms, but to do so they must overcome the normally automatic coordination between accommodation (focus of the eyes) and horizontal vergence (angle of the eyes).

The illusion is one of depth perception and involves stereopsis: depth perception arising from the different perspective each eye has of a three-dimensional scene, called binocular parallax.Ībout 5% of people have disordered binocular vision that prevents them from seeing the depth in autostereograms or in conventional stereograms viewed through a stereoscope. To illustrate the depth for such people, the second image has had the binocular parallax replaced by motion parallax: the alteration in the position of points in the scene at different distances from a viewer's eyes as the viewer's head moves. The simplest type of autostereogram consists of horizontally repeating patterns (often separate images) and is known as a wallpaper autostereogram. When viewed with proper vergence, the repeating patterns appear to float above or below the background. The well-known Magic Eye books feature another type of autostereogram called a random dot autostereogram, similar to the first example, above.

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