Researchers found that muscles move to orient ears toward sound source in vestigial reaction
By: Nicola Davis
Published: Jan 31, 2025
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 then 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.”
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Recently, electromyographic (EMG) signals of auricular muscles have been shown to be an indicator of spatial auditory attention in humans, b
Abstract
Recently, electromyographic (EMG) signals of auricular muscles have been shown to be an indicator of spatial auditory attention in humans, based on a vestigial pinna-orienting system. Because spatial auditory attention in a competing speaker task is closely related to the more generalized concept of attentional effort in listening, the current study investigated the possibility that the EMG activity of auricular muscles could also reflect correlates of effortful listening in general. Twenty participants were recruited. EMG signals from the left and right superior and posterior auricular muscles (SAM, PAM) were recorded while participants attended a target podcast in a competing speaker paradigm. Three different conditions, each more difficult and requiring a higher amount of effortful listening, were generated by varying the number and pitch of distractor streams, as well as the signal-to-noise ratio. All audio streams were either presented from a loudspeaker placed in front of the participants (0°), or in the back (180°). Overall, averaged PAM activity was not affected by different levels of effortful listening, but was significantly larger when stimuli were presented from the back, as opposed to the front. Averaged SAM activity, however, was significantly larger in the most difficult condition, which required the largest amount of effort, compared to the easier conditions, but was not affected by stimulus direction. We interpret the increased SAM activity to be the response of the vestigial pinna–orienting system to an effortful stream segregation task.
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tl;dr Evolution is true.
Our ears no longer need to move because we have flexible necks. Evolution tends to favor specialization rather than a "middle ground." You will not, for example, find species with slightly flexible necks and slightly mobile ears. They will have lost out to those with highly flexible necks with immobile ears, and those with highly mobile ears but largely fixed necks.
This is also the same reason anisogamy - large, resource-rich immobile ova which pairs with small motile sperm - has evolved repeatedly and independently across species. Medium size gametes with a bit of mobility will always lose out to the two extremes.
