SACHA PFEIFFER, HOST:
If you hear something interesting, you might prick up your ears. That's a figurative expression, of course. People's ears don't actually move upward. But NPR's Nell Greenfieldboyce found that this old term seems to hold a bit of truth.
NELL GREENFIELDBOYCE, BYLINE: While taking horseback riding lessons recently, Steven Hackley got this advice - pay close attention to the horse's ears. He says anyone with a pet understands why. You can learn a lot by tracking the movement of an animal's ears.
STEVEN HACKLEY: So you can tell which direction a cat or a dog is paying attention to. You can also pick up on emotions.
GREENFIELDBOYCE: Hackley is a researcher with the University of Missouri. He says, in almost every species, lifting up the ears is a clue...
HACKLEY: ...That the animal is putting some work into it. They're paying close attention. They're concentrating.
GREENFIELDBOYCE: So what about humans? People have some vestigial muscles around the ear. They never get used, except by those people who are able to deliberately wiggle their ears as a party trick. Hackley is part of a research team that put electrodes on those muscles to record subtle electrical signals.
HACKLEY: In this experiment, we recorded from two different ear muscles - one that raises the ears up and one that pulls the ear back.
GREENFIELDBOYCE: Twenty volunteers got wired up with electrodes around their ears and sat in a lab surrounded by speakers. They were told to pay attention to a certain audiobook. Andreas Schroer, of Saarland University in Germany, says the audiobook was picked to be engaging.
ANDREAS SCHROER: Fun little trivia that people could actually motivate themselves to listen to.
GREENFIELDBOYCE: He says, after a little while, though, other sounds got faded in at different volumes. These were picked to be distracting.
SCHROER: Those were also some podcasts we got. One of them was actually about the history of podcasts.
GREENFIELDBOYCE: The goal was to create levels of difficulty in listening as the volunteers tried to tune in to that fun audiobook. Hackley says, as the listening task got easier and harder, the researchers saw changes in the signals to one particular ear muscle.
HACKLEY: The muscle that lifts the ear upwards, that perks the ear - it varied according to the amount of effort that the subject put inn the task.
GREENFIELDBOYCE: It was as if the body was doing its best to perk up the ears, just as our evolutionary ancestors would have done, even though we lost this ability about 25 million years ago. What's more, when listeners were trying to pay attention to sound coming from a speaker behind them, that other ear muscle showed electrical activity - that muscle that, in animals, pulls the ear back. These results appear in the journal Frontiers In Neuroscience.
Alex Francis is a professor of speech, language and hearing sciences at Purdue University, who wasn't part of the research team. He says having a new way to measure how much effort someone is making in order to listen could be very important because trying to hear can sometimes be so exhausting and frustrating people just give up.
ALEX FRANCIS: We have very, very good hearing aids now. They can provide very, very good amplification, and yet people still aren't happy wearing them sometimes. People sometimes still find it more challenging to listen through a hearing aid.
GREENFIELDBOYCE: But if a hearing aide could monitor these muscles around the ear, the device could potentially get information about how a person was experiencing the act of listening and then make adjustments that could help. Nell Greenfieldboyce, NPR News.
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