Autostereograms are optical illusions of depth that are designed to trick the brain into perceiving a three-dimensional scene in a two-dimensional image. The simplest type, known as a wallpaper autostereogram, consists of horizontally repeating patterns that appear to float in the air above the background. In order to perceive the 3D shapes, the brain must overcome the normally automatic coordination between focusing and convergence. What are the two ways that an autostereogram can be viewed? Discuss
Source: The Free Dictionary