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Body + BrainBody & Brain

Poof! Science reveals how easily a magician can fool you

ByAJ FilloNOVA NextNOVA Next

A magician transforms one card into another. Is it magic or science? Image credit: Emily Zendt, WGBH

With a simple gesture, a magician can transform a playing card right in front of your eyes. But the illusion isn’t magic—it’s science.

A study published earlier this year in the journal Psychological Science reveals that no matter how closely you watch a magic trick, you’ll probably miss the sleight of hand.

Imagine a magician waves a card back and forth, seemingly causing it to transform into another card. The small motion, swapping one playing card for another, is hidden by the larger motion happening at the same time, the wave of a hand (like in the video below). This illusion exploits a phenomenon called change blindness, which refers to a viewer not noticing a change in visual stimuli.

The magician swaps the card at the moment their hand changes direction. That abrupt change in direction is all the misdirection they need to distract the audience from their sleight of hand, says Katherine Wood, an author of the recent study and PhD candidate in psychology at the University of Illinois.

This is possible because our brains don’t process everything our eyes see.

“The illusion that we’re always seeing everything all the time is such a powerful part of who we are,” says Stephen Goldinger, a psychologist at Arizona State University who was not involved in the study. Although we feel like we see everything, he says, we only see snapshots of the world around us. “Our brains are remarkably adept at filling in the background.”

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This concept of change blindness isn’t new. Studies like the famous selective attention test, in which people watching one action or activity fail to notice a person in a gorilla suit walk through the background, have demonstrated change blindness in much more complex scenarios. But this is the first time change blindness has been studied in a scenario as simple as a single motion concealing a single change, says Richard Yao, lead author on the study.

In the study, the researchers had 21 undergraduate students watch a set of six dots moving as a group across a screen. One of the dots would abruptly rotate 15 degrees while the other five stayed the same. The team asked the students to pick out the rotating dot.

Although it didn’t happen every time, the participants usually fell victim to change blindness and misidentified the rotating dot. The change blindness effect observed in this study was incredibly strong, says Anthony Barnhart, a psychologist at Carthage College who was not involved in the study.

Studies like this, Barnhart says, are important in helping understand how we’re able to perceive the world. “In many ways, magicians have a head start on psychologists when it comes to how the brain works,” he says.

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