What is a stereogram?
We can fool the visual system by presenting two 2D images, one to each eye, which contain the same objects but viewed from slightly different angles (disparity). When we present this to an observer where the left eye only sees the left image and the right eye only sees the right image, the brain fuses these images to create the sense of depth. The devices used to view stereoscopic images are called stereoscopes. In a way, red-green glasses used to perceive anaglyphs are a kind of stereoscope. If we want to measure only stereopsis and eliminate the monocular depth cues mentioned earlier then we can use random-dot stereograms which is what we use in the present chart. These stereograms are sometimes called Julez-type stereograms because Julez was the first to use such images to isolate stereopsis and demonstrate that the brain was capable of seeing depth without having prior information on the image except disparity.
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Jocelyn Faubert, Ph.D.
e-mail: jocelyn.faubert@umontreal.ca