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.
"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."
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."