Magicians use the science of misdirection to trick our eyes | NOVA

With a simple gesture, a magician can transform a playing card before your eyes. But the illusion is not magic, it is science.

A study published earlier this year in the magazine Psychological Sciences reveals that no matter how carefully you watch a magic trick, you’ll likely miss the sleight of hand.

Imagine that a magician waves a card back and forth, seemingly causing it to transform into another card. The small movement, exchanging one playing card for another, is masked by the larger movement occurring at the same time, the gesture of a hand (as seen 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 exchanges the card when his hand changes direction. That sudden change in direction is all they need to distract the audience from their sleight of hand, says Katherine Wood, author of the recent study and a PhD student in psychology at the University of Illinois.

This is possible because our brain does not process everything our eyes see.

“The illusion that we always see 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 seem to see everything, he says, we only see snapshots of the world around us. “Our brains are remarkably good at filling in the background.”

This concept of change blindness is not new. Studies like the famous selective attention test, in which people watching an action or activity fail to notice that a person in a gorilla costume is walking across the background, has demonstrated change blindness in much more complex scenarios. But this is the first time that change blindness has been studied in such a simple scenario as a single movement concealing a single change, says Richard Yao, lead author of the study.

In the study, the researchers had 21 undergraduate students look at a set of six points moving in a group on a screen. One of the points suddenly rotated 15 degrees while the other five remained the same. The team asked the students to choose the turning point.

Although it didn’t happen every time, participants generally experienced change blindness and misidentified the turning point. 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, says Barnhart, are important in helping to understand how we are able to perceive the world. “In many ways, magicians are way ahead of psychologists when it comes to brain function,” he says.

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Brian L. Hartfield