"Cups and Balls," a magic illusion in which balls appear and disappear under the cover of cups, is one of the oldest magic tricks in history, with documented descriptions going back to Roman conjurors in 3 B.C. The trick has many variations, but the most common one uses three balls and three cups. The magician makes the balls pass through the bottom of cups, jump from cup to cup, disappear from a cup and turn up elsewhere, turn into other objects, and so on. The cups are usually opaque and the balls brightly colored.
Recently, we conducted the first, long overdue, neuroscientific study of this trick in my laboratory, using a video filmed in magician duo Penn & Tellers theater in Las Vegas. Penn & Teller perform a striking variant of the Cups and Balls illusion, first with three opaque and then with three transparent cups. The transparent cups mean that visual information about the loading of the balls is readily available to the brain, yet the spectators still cannot see how the trick is done!
Our experiments tracked when and where observers looked during some of Teller's signature moves. By quantifying how well observers tracked the loading and unloading of balls with and without transparent cups, we determined that some aspects of the illusion were even more powerful at controlling attention than those originally predicted by Teller.
Magicians have performed and systematically developed the art and theory of this illusion for thousands of years, but each new generation of conjurers offers new insights and hypotheses about how and why it works for the audience. Our results advance our understanding of magic misdirection and we hope that they will aid magicians as they work to hone their art.
The study, titled Perceptual elements in Penn and Tellers Cups and Balls magic trick, was published as part of the recent launch of PeerJ, a new peer-reviewed open-access journal in which all articles are freely available to everyone.
To read more about our collaboration with magicians to better understand the brain, check out our book, Sleights of Mind.