Stephen L. Macknik, Barrow Neurological Institute

Neuroscientists studied the classic "cups and balls" illusion performed by Teller.Stephen L. Macknik, Barrow Neurological Institute

By studying a magic trick that has been around for thousands of years, neuroscientists have shed light on human attention and visual systems -- as well as on the trick, itself.

"Magicians, in particular, are very intellectual performance artists. They are very interested in the mind and how behavior happens," Dr. Stephen Macknik, director of the Laboratory of Behavioral Neurophysiology at the Barrow Neurological Institute(BNI), told Discovery News. "What scientists are doing when we study perception is pretty much the same thing, except we're using the scientific method."

The hope is that magicians' intuitive insight could help instruct the field of neuroscience and perhaps, even be applied in medicine to help people with attention deficit issues.

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In their study, recently published in the inaugural issue of PeerJ, the researchers focused upon a famous trick by a pair of very famous magicians. Penn & Teller's 10-year run at The Rio All-Suite Hotel & Casino has made them one of the longest-running and most beloved acts in Las Vegas history.

Their trick, "Cups and Balls," is a classic illusion performed by Roman magicians as far back as 2,000 years ago when gladiators still battled in the Colosseum.

While the trick has many derivatives, the most common uses three brightly colored balls and three opaque cups. Using sleight-of-hand, the magician seemingly makes the balls pass through the bottoms of cups, jump from cup to cup, disappear and reappear elsewhere or turn into entirely different objects. In Penn & Teller's case, that different object is often a potato.

By studying the magic trick, Cups and Balls, scientists hoped to gain insight into the brain.Getty Images

One day, while he was messing around with an empty water glass and a wadded-up paper napkin as a ball, Teller devised a new variation on the trick using transparent cups. The idea being that, even though audiences could see the balls being moved around, the magician's sleight-of-hand misdirected the attention so much that the mind was still fooled.

In fact, Teller even tricked himself. During one manipulation, he turned a glass upside down and put a napkin ball on top. Then he tilted the glass so that the ball fell into his other hand. As it fell, the ball's trajectory was so compelling that it drew his attention away from his original hand, which was loading a second ball under the glass.

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He figured if he could fool himself, then he could surely fool an audience, and thus the transparent "Cups and Balls" trick was born.

"Teller thought there was something particularly compelling about the drop of the ball -- that falling objects and gravity have a special place in how our attention is captured," said Dr. Susana Martinez-Conde, director of the Laboratory of Visual Neuroscience at BNI and co-author of the study.

So Macknik and Martinez-Conde -- their own duo of sorts, as in husband and wife -- set out to investigate Teller's hypothesis that the falling ball generated a stronger misdirection of the attention than alternative manipulations.

Both Macknik and Martinez-Conde are no strangers to the crossroads of neuroscience and magic. For years, they've written and experimented extensively on this intersection and continue to do so today. Both are columnists for the Scientific American and co-authors of the book "Sleights of Mind."

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"Our previous experiments were about discovering new things in science using magic," said Macknik. "This was the first study that we did that was specifically for studying something important about magic using science."

For their experiment, seven participants watched a video of Teller performing the "Cups and Ball" trick. Teller used his right hand to introduce, or load, a small ball inside each of two upside down cups while simultaneously using his left hand to remove a different ball from the upside-down bottom of the cup.

Neuroscientists studied the classic "cups and balls" illusion performed by Teller.Stephen L. Macknik, Barrow Neurological Institute

The sleight-of-hand on the third cup involved one of six manipulations: the standard maneuver (ball falling into Teller's hand), the standard maneuver without a third ball, a ball placed on the table before going into Teller's pocket, a ball lifted before going into Teller's pocket, a ball dropped to the floor and a ball stuck to the cup with a piece of adhesive.

By pressing one of two buttons, participants indicated whether balls were removed from the cups/table or placed inside the cups/on the table. During the experiment, participants' eye movements were also recorded with a non-invasive, video-based eye tracker.

Contrary to Teller's expectations, neither the falling ball nor the enhanced version where the ball fell to the floor generated the strongest misdirection of the attention. Actually, the manipulation that caused the most gaze misdirection was when the ball was lifted.

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"What was surprising for us was that the original motivation of the study didn't pan out," Martinez-Conde said. "You can think of all sorts of adaptive, evolutionary reasons why falling objects are more compelling than other types of falling motions, but that didn't turn out to be the case."

Another manipulation that the study made was to cover Teller's face. This meant his gaze position couldn't inform the subjects about what to pay attention to, which is thought to be very important to this trick.

"When he covered his face, it didn't change anything," Macknik said. "So this suggests that the joint attention from body movements and gaze position don't seem to be interacting in the brain."

Even so, isn't a disproved hypothesis somewhat of a let-down? Far from it says Macknik.

"Just like in science, you can have theories that you fully expect an experimental result and often times you're really surprised by the outcome," he said. "I think it really shows that magic can benefit from putting the scientific method to it."

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And as the art of magic benefits, so do the artists.

"If a magician wants to know what is going to misdirect the audience's attention, then it's this information that they will find valuable to them," said Martinez-Conde.

But what does it matter in the big picture if Penn & Teller can conjure a little hocus-pocus?

"The benefit here is that magicians know a lot about cognition. They know it implicitly. They don't explicitly know, necessarily, about how the brain works, but that's where the neuroscientists come in," said Macknik. "By learning what magicians already know, they can combine it with their knowledge in neuroscience and things can get done faster."

For starters, one of these "things" that can potentially get done faster is discovering more about joint attention, which is the way we pay attention to other people and objects by means of eye-gazing, pointing or other verbal or non-verbal signals.

It's known that people with some conditions, including autism, have a deficit in maintaining this kind of attention.

"We can be informed by what magicians already know about the mind," he said. "They've been doing it for thousands of years now and cognitive science has been here for only 35 years or so. There's a lot of fertile ground there."