Imma Perfetto
Cosmos science journalist
While some humans have the hilarious ability to wiggle their ears, most cannot move their auricular muscles at will. But new research suggests we unconsciously engage these muscles when listening very intently.
Some species, such as cats and dogs, can change the shape of the pinna – the shell of the ear – to help funnel sound into the eardrums. Our primate ancestors could do it but lost the ability millions of years ago. So, modern humans’ auricular muscles have become vestigial – no longer serving a purpose.
“The exact reason these became vestigial is difficult to tell, as our ancestors lost this ability about 25 million years ago,” says Andreas Schröer of Saarland University, Germany, first author of the study in Frontiers in Neuroscience.
“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.”
The new study suggests humans’ auricular muscles may not be as useless as we thought.
“There are 3 large muscles which connect the auricle [shell of the ear] to the skull and scalp and are important for ear wiggling,” says Schröer.
Previous research has already shown that the largest ones, the superior and posterior auricular muscles, react during attentive listening.
The team recruited 20 people without hearing problems to determine whether these muscles are more active during difficult listening tasks.
They applied electrodes to participants’ auricular muscles and simultaneously played an audiobook and distracting podcast recordings from speakers in front of or behind the participant.
In the easiest trial, the podcast was quieter than the audiobook and the speaker’s voice was a stronger contrast to the audiobook. To create a medium and difficult mode, the scientists added a podcast that sounded more like the audiobook and made the distractions louder.
Participants’ self-reported effort, and how often they lost track of the audiobook, increased in line with the difficulty of the task. The accuracy of their responses to questions about the audiobook also dropped noticeably between the medium and the difficult mode.
They found that the 2 auricular muscles reacted differently to these conditions. The posterior auricular muscles, which pull the ear backwards, reacted to changes in direction. Whereas the superior auricular muscles, which pull the ear upwards, became more active during the difficult mode.
This suggests the activity of the muscle could provide an objective measure of listening effort in cognitive neuroscience research. However, it’s unclear if the movements help people hear better.
“The ear movements that could be generated by the signals we have recorded are so minuscule that there is probably no perceivable benefit,” says Schröer.
“However, the auricle itself does contribute to our ability to localise sounds. So, our auriculomotor system probably tries its best after being vestigial for 25 million years but does not achieve much.
“This suggests that these muscles are engaged not merely as a reflex but potentially as part of an attentional effort mechanism, especially in challenging auditory environments.”
The team plans to carry out further research to confirm these results in larger, more diverse participant groups and under more realistic conditions.
“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,” says Schröer.
“The effect of these factors in people with hearing impairments would also be interesting to investigate.”
