Béla Julesz

Around 1956, Julesz began at Bell Labs on a project to detect patterns in the output of random number generators. He decided to try mapping the numbers into images and using the pattern-detecting capabilities of the human visual system to look for a lack of randomness.Julesz noticed that two identical random images when viewed through a stereoscope, appeared as if they were projected onto a uniform flat surface. He experimented with the image pair by shifting a square area in the center of one of the images by a small amount. When he viewed this pair through the stereoscope, the square appeared to rise out from the page. (Wikipedia, "Random dot stereogram")