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Wiggling your ears might be more of a pub party piece than a survival skill, but humans still try to prick up their ears when listening hard, researchers have found.
Ear movement is crucial in many animals, not least in helping them focus their attention on particular noises and work out which direction they are coming from.
But while the human ear is far more static, traces of our ancestors’ ear-orienting system remain in what has been called a “neural fossil”.
“It is believed that our ancestors lost their ability to move their ears about 25m years ago. Why, exactly, is difficult to say,” said Andreas Schröer, the lead author of the research from Saarland University in Germany.
“However, we have been able to demonstrate that the neural circuits still seem to be present in some state, [that is] our brain retained some of the structures to move the ears, even though they apparently are not useful any more.”
The team previously found the movement of these muscles in humans is related to the direction of the sounds they are paying attention to. Now, they have found that some of these muscles become activated when humans listen hard to a sound.
Writing in the journal Frontiers in Neuroscience, the team reported how they asked 20 adults without hearing problems to listen to an audiobook played through a speaker at the same time as a podcast was played from the same location.
The team created three different scenarios: in the “easiest” scenario the podcast was quieter than the audiobook, with a large difference in pitch between the voices. In the “hardest” scenario, two podcasts were played which, taken together, were louder than the audiobook, with one of the podcasts spoken at a similar pitch to the audiobook.
“We were interested in finding out if the auriculomotor system in humans is sensitive to effortful listening. Think about trying to understand what someone is saying in an almost empty restaurant, and the trying to understand someone in a very busy restaurant,” said Schröer.
Each participant experienced the three different scenarios twice. This was then repeated with the speaker in a different position in the room. Each participant wore a set of electrodes, allowing the researchers to record the electrical activity produced by the muscles involved in wiggling the ears.
After each trial, participants were asked to rate how much effort they spent listening to the audiobook.
The results revealed that the participants’ perceived listening effort, and how often they lost focus on the audiobook, increased as the scenario moved from easiest to hardest.
The team found activity in the superior auricular muscles, which lift the ear upwards and outwards, was larger during the most difficult listening conditions than during the easy and medium conditions. They also found the posterior auricular muscles, which pull the ear backward, were more active when the sounds came from behind the participant than in front of them.
“Almost nobody [in the study] had the ability to voluntarily move their ears, so our results are not related to a person’s ability to do this,” said Schröer, although he noted other research has shown people can learn to move their ears.
While the study is small, and needs to be repeated in a larger and more diverse group, the team said the findings provided insights.
“The ear movements that could be generated by the signals we have recorded are so minuscule– or even absent– that there is probably no perceivable benefit,” said Schröer. “So we think that this vestigial auriculumotor system is ‘trying its best’, but probably doesn’t achieve much.”
