In the year 1993, Congress passed NAFTA, the Buffalo Bills lost their third consecutive Super Bowl, Lorena Bobbitt grabbed a knife from the kitchen, and the world witnessed the birth of a pop-culture phenomenon based on an optical illusion. It was Magic Eye.
These pictures, known in the vision literature as autostereograms, carry a hidden 3D image, discernible only when the viewer arranges their eyeballs in a particular way. Cheri Smith and Tom Baccei created the "Magic Eye" brand that contributed to their popular success in the '90s, but stereograms weren't new.
Their lineage goes back to the 19th-century discovery of stereopsis — the depth information we get from having two eyes spaced slightly apart. This is the feature of visual perception that's manipulated by devices like the View-Master, the red novelty toy that comes with a reel of tiny dual photos. The original View-Master was the Victorian stereoscope, and it was as popular in the late 1800s as Magic Eye was in the 1990s.
Oliver Wendell Holmes Sr. was so enamored with the stereoscope that he created his own non-patented version of the toy and popularized it in the United States. Among his many meditations on the technology, he wrote:
[T]he shutting out of surrounding objects, and the concentration of the whole attention, which is a consequence of this, produce a dreamlike exaltation of the faculties, a kind of clairvoyance, in which we seem to leave the body behind us and sail away into one strange scene after another, like disembodied spirits.
Holmes would have loved Nintendo 64.
The Victorian stereographs were typically photos or simple drawings. The real innovation on the path toward Magic Eye was research conducted by Bela Julesz in the late 1950s. Working at Bell Laboratories, Julesz showed that the depth perception from stereographs could be divorced from the depth cues we get from a photo, like shading, overlap, perspective lines, and relative sizes. And he demonstrated that by inserting depth into random noise: the random-dot stereogram:
These random dots contain a hidden shape that you can see if you diverge your eyes to point each eye at its own square. You should see three copies of the square rather than two or four, and the hidden image will appear inside the middle square. (Note: This isn't easy. Julesz would have originally viewed these through a stereoscope that delivers one image separately to each eye, but if you practice enough, you can "free-fuse" them).
From that point, the next step was to re-create the hidden-picture effect in a single image, rather than two images that require hardware to view. A few iterations later and you've got Elaine Benes and Ross Gellar making jokes about stereograms in their respective fictional worlds.
To learn more about the history of stereograms and see exactly how they work, watch the video at the top of this post or on our YouTube channel.