“Gazing at wallpaper with small repetitive motifs, [David Brewster] observed [as early as 1844] that the patterns might quiver or shift, and then jump into startling stereoscopic relief, especially if these patterns were offset in relation to one another. Such “autostereograms” have probably been experienced for millennia. . . . Medieval manuscripts such as the Book of Kells or the Lindisfarne Gospels, for example, contain exquisitely intricate designs done so exactingly that whole pages can be seen, with the unaided eye, as stereoscopic illusions. (John Cisne, a paleobiologist at Cornell, has suggested that such stereograms may have been “something of a trade secret among the educated elite of the seventh and eighth century British Isles.”)”

—Oliver Sachs, Stereo Sue: Why Two Eyes are Better than One, The New Yorker, June 19, 2006.