They wiggle, though they don’t do much else. That’s what we’ve long thought about the auricular muscles — the useless ear muscles that once helped our ancient ancestors hear. But recent research in Frontiers in Neuroscience reveals that these muscles are still trying hard to help us, activating during difficult listening situations.
“There are three large muscles [that] connect the auricle [the outer ear] to the skull and scalp,” said Andreas Schröer, a study author and a neuroscientist at Saarland University in Germany, in a press release. “These muscles, particularly the superior auricular muscle, exhibit increased activity during effortful listening tasks.”
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Made For More Than Wiggling
In modern humans, auricular muscles aren’t all that useful. We use them to wiggle our ears (or, some of us do), and that’s about all. (Wiggling, as it turns out, isn’t a universal skill.) But millions of years ago, our distant ancestors employed these muscles to move their ears around, twisting and turning them towards sound.
“The exact reason these became vestigial is difficult to tell, as our ancestors lost this ability about 25 million years ago,” Schröer said in the release. “One possible explanation could be that the evolutionary pressure to move the ears ceased because we became much more proficient with our visual and vocal systems.”
While we can’t contort our ears in the same way today, some of us sure can wiggle them, suggesting that these muscles are still active. Testing their abilities in 2020, Schröer and a team of researchers demonstrated that these muscles activated during listening tasks that featured sounds from different directions. But what about during difficult listening, when several sounds occur at once?
To determine whether the activity of these muscles depends on the difficulty of the task, Schröer and a team turned to electromyography, a method that uses electrodes to monitor the electrical activity in muscle tissues. Their results revealed that the more difficult the task, the more active the muscles, at least for the superior auricular muscles.
“This suggests that these muscles are engaged not merely as a reflex but potentially as part of an attentional effort mechanism,” Schröer said in the release, “especially in challenging auditory environments.”
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When Hearing Is Hard
To arrive at their results, the researchers enlisted the help of 20 hearing participants. Applying electrodes to their auricular muscles, the team measured their muscle activity as they listened to an audiobook and a podcast at the same time. The audio played from separate speakers, placed in front of the participants or behind, and each participant listened to 12 trials, separated into three different levels of difficulty.
The audiobook was a lot louder than the podcast in the easy trials, and the speakers’ voices were distinct. But in the moderate and difficult trials, the audiobook was only a little louder than the podcast, and the speakers’ voices were similar.
As the difficulty level of the task increased, so, too did the activity of the superior auricular muscles. Though they remained relatively inactive during the easy and medium trials, the difficult trials saw a surge in their activity.
According to the researchers, their activation also correlated with the participants’ self-assessments and comprehension scores. When the participants were asked to assess the amount of listening effort that they expended in the trials, they reported their effort increased with trial difficulty. And when they were asked to take tests on the audiobook’s content, their scores declined in step with the incline in the difficulty of the task.
Effort in Listening
Further research is required to confirm the team’s results, and to conclude whether the activity is tied to any actual improvements in listening (though Schröer says that it probably isn’t).
“The ear movements that could be generated by the signals we have recorded are so minuscule that there is probably no perceivable benefit,” said Schröer in the press release. “Our auriculomotor system probably tries its best after being vestigial for 25 million years, but does not achieve much.”
Though it isn’t likely that this activity helps hearing, it could help hearing research, as the superior auricular muscles could serve, the team says, as an indicator for increased levels of effort in listening.
“Investigating the possible effects of muscle strain itself or the ear’s miniscule movements on the transmission of sound is something we want to do in the future,” Schröer said in the release. “The effect of these factors in people with hearing impairments would also be interesting to investigate.”
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Frontiers in Neuroscience. Electromyographic Correlates of Effortful Listening in the Vestigial Auriculomotor System
eLife. Vestigial Auriculomotor Activity Indicates the Direction of Auditory Attention in Humans
Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
Tama Howe
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