When people are trying hard to listen to something, the body seems to do its best to "prick up its ears," even though this ability was lost by our evolutionary ancestors millions of years ago.
That's according to a new study which found that a certain vestigial ear muscle — one that perks up ears in animals — actually shows electrical activity when people engage in a difficult listening task.
"Lifting the ears up straight is, in almost every species, a clue that the animal is putting some work into it. They're paying close attention, they're concentrating," says Steven Hackley, a researcher with the University of Missouri.
Humans can't move their ears around in the same way that dogs, cats and horses do. But people do have certain muscles around the ear that never get used, except by those people who are able to deliberately wiggle their ears as a party trick.
Recently, Hackley and some colleagues looked to see if they could record subtle electrical signals in those muscles, by putting electrodes on them.
"In this experiment, we recorded from two different ear muscles," says Hackley. "One that raises the ears up, and one that pulls the ear back."
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, which was picked to be engaging. Andreas Schroeer of Saarland University says this audiobook was full of "fun little trivia that people could actually motivate themselves to listen to."
After a little while, though, other sounds faded in, at different volumes. These were picked to be distracting podcasts. "One of them was actually about the history of podcasts," says Schroeer, who notes that people later reported how much difficulty they had in listening at different times.
As the listening task got easier and harder over the course of this experiment, the researchers saw changes in the electrical activity in the ear muscle that, in animals, perks the ear up.
"It varied according to the amount of effort that a subject put into the task," says Hackley.
What's more, when listeners were trying to pay attention to sound coming from a speaker behind them, the other ear muscle they monitored showed electrical activity — the muscle that, in animals, pulls the ear back.
These results, in the journal Frontiers in Neuroscience, intrigued other experts in hearing and the effort it can take to listen.
Professor of speech, language and hearing sciences Alexander Francis is at Purdue University and wasn't part of the research team. He, says that it could be very useful to have a new way to objectively measure how much effort a listener has to make.
Even with hearing aids, says Francis, the work of trying to listen can sometimes be so exhausting and frustrating that people just give up.
"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," says Francis.
If a hearing aid could monitor activity in these vestigial muscles around the ear, the device could potentially get information about how a person was experiencing the act of listening and then make adjustments accordingly.
Audiology professor Matthew Winn at the University of Minnesota, says that currently, the main way researchers have to measure the effort of listening is to monitor pupil dilation, since the pupils dilate anytime someone pays close attention to something. But this laboratory technique would be hard to carry out into the real world.
He finds the data in this new study convincing, but wonders if these registers of electrical activity are truly measuring listening effort, rather than just a physiological response to a stimulus such as a sound getting louder.
"It's possible that in this study they were measuring people's report of their frustration with the noise, even if it wasn't exactly the effort of listening to the speech," Winn says, though he notes that since the volunteers were questioned about their experiences and reported that their efforts varied, it's "tempting" to make the link.
Still, he thinks more experiments could tease all this out. And he thinks finding better ways to measure the effort of listening is critical, as a lot of people with hearing difficulties don't even realize how much energy they expend just trying to hear.
"What they notice is that, you know, they get home from work and they're really tired or they don't have the energy to clean up the house or things like that," says Winn. "They might not even attribute it to their own hearing fatigue. But that turns out to be the common link across a lot of these experiences."
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