If you want to confuse someone, turn the thing they’re seeing upside-down.
The abilities we’ve evolved to spot and judge movement don’t work if we’re looking at an image the wrong way.
Unless you’re an astronaut, or, according to new research in Scientific Reports, a vertical dancer.
Vertical dance is a form of the art where the dancer is suspended from a rope or a cable, and can move up and down a wall or cliff face as well as from side to side.
The new research finds that vertical dancers’ biological motion perception (BMP) works in more dimensions than ordinary dancers or non-dancers.
“BMP is intriguing because it is a survival skill humans and animals both share,” says co-author Qin Zhu, a professor of kinesiology at the University of Wyoming, US.
“We can read the motions produced by others in same or different species and figure out who the actor is and what is intended by the actor. So, we can better prepare our response, either to escape or engage.
“However, if the motion is performed upside-down, or inverted, such a capability will be greatly impaired.”
Read more: Dance that’s really (fluid) dynamic
The researchers asked 16 vertical dancers, 21 traditional dancers, and 15 non-dancers to view videos of dance movements, both in the air and on the ground.
The movements were shown as point-light displays: instead of a person or the outline of a person, the videos showed lights representing joints and limbs.
Half of the displays were turned upside-down. Participants were asked to identify whether the movement was inverted or not.
Traditional dancers and non-dancers were equally good as each other at spotting which moves had been flipped for ground-based dance moves.
But only vertical dancers could spot the inversions when they happened in the air.
This reflects research published earlier this year showing that astronauts who’d spent time in zero gravity could better spot upside-down point-light displays – some compensation for the eye damage which happens in space.
The researchers believe that watching a lot of these inverted dance moves can help to understand the movements, as well as performing them.
“Therefore, spectators who have seen vertical dance performances before will have a better understanding of inverted movements than those who have never seen such a performance,” says Zhu. “And, for those who want to learn and perform vertical dance in the future, both visual and motor training – with respect to the inverted movements – are required to improve awareness and perception of self-movements in relation to partners or spectators while performing vertical dance.”
Ellen Phiddian is a science journalist at Cosmos. She has a BSc (Honours) in chemistry and science communication, and an MSc in science communication, both from the Australian National University.
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