Magic-Trick Science, Half-Brain Sleep | March 11, 2013 Issue - Vol. 91 Issue 10 | Chemical & Engineering News
Volume 91 Issue 10 | p. 40 | Newscripts
Issue Date: March 11, 2013

Magic-Trick Science, Half-Brain Sleep

Department: Newscripts
Keywords: Magic, neuroscience, Penn and Teller, illusion, sleep science, neurotransmitters, fur seals, serotonin

For ages, magicians have bewildered audiences with sleight of hand, causing observers to ask, “How’d they do that?” Little did folks know, some magicians aren’t entirely sure either.

A team of cognitive neuroscientists recently collaborated with Teller, the silent half of famed magic duo Penn & Teller, to answer a burning question he had about one of his tricks. Teller wanted to know why his version of the classic “cups and balls” illusion—a trick that dates back to Rome in 3 B.C.—fools people as well as it does.

During the trick, Teller sets one small ball on top of each of three overturned cups. He then picks up a cup with one hand and tilts it so the ball falls into his other hand. At the same time, the hand holding the cup slips a new ball underneath it and places it back on the table. The magician follows suit with the other cups and, finally, reveals the hidden balls with a flourish.

See Teller perform “cups and balls” at

Teller had postulated that the trick works—even with transparent cups—because observers watch the falling ball rather than his hands. The research team, led by Stephen L. Macknik of the Barrow Neurological Institute, in Arizona, tested that idea by showing experiment participants videos of Teller performing the illusion and tracking their eye movements.

Surprisingly, Teller’s guess about the success of “cups and balls” was incorrect: The researchers demonstrated that a person’s eyes don’t stray far from the magician’s hands (PeerJ, DOI: 10.7717/peerj.19). Eyes did stray, however, when Teller lifted a ball away from the top of a cup.

Just because Teller’s intuition was wrong, Macknik tells Newscripts, doesn’t detract from the magician or his tricks. “One of the purposes of science is to overcome common sense and intuition,” Macknik says. “If these were always correct, science would have a very small role in life.”

Fur seal: Whole-brain sleep if by land, half-brain sleep if by sea.
Credit: Shutterstock
Photo of a fur seal resting on land.
Fur seal: Whole-brain sleep if by land, half-brain sleep if by sea.
Credit: Shutterstock

Fur seals have also been baffling scientists with sleight of brain they perform while asleep. Activity across a seal’s entire brain dampens when the animal sleeps on land, just as it does for humans. But when a seal is in water, half of its brain sleeps while the other half remains active.

The “cute thing” about the phenomenon, says Jerome M. Siegel, a neurobiologist at the University of California, Los Angeles, who studies seals, is that “when they’re in water, you can tell which sides of their brains are asleep” just by looking at the animals. Similar to humans, the right side of the brain controls movement on the left side of the body and vice versa. So if a seal’s left flipper is moving to keep its head above water but the other flipper is immobile, the left hemisphere of the critter’s brain is asleep, Siegel explains.

When the animals take an aquatic nap, they also keep one eye open. “We think the function of this sleep state is to allow the animals to stay vigilant in the water,” Siegel says. “Fur seals are often eaten by sharks.”

Along with an international team of researchers, Siegel recently took advantage of seals’ asymmetric brain behavior to study the chemistry of sleep. By monitoring the brain waves and circulating neurotransmitters in the noggins of four seals, the team determined that acetylcholine—the same chemical that causes muscles to contract—decreases on the sleeping side of the brain (J. Neurosci., DOI: 10.1523/jneurosci.2603-12.2013). Serotonin, a neurotransmitter frequently linked to sleep, remained at the same level across the seals’ brains during their watery slumber, however.

“Many health food stores sell serotonin as something to induce sleep,” Siegel says. According to the results, he adds, this practice is likely nonsensical.


Lauren Wolf wrote this week’s column. Please send comments and suggestions to

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