Long believed to be inactive or vestigial, scientists believe that the muscles behind the human ear are actually activated when people listen intently, according to a study published in the Frontiers in Neuroscience. This muscle, known as the auricularis posterior, has been largely dormant in humans for centuries but shows signs of reactivation when individuals focus on challenging auditory tasks.
“There are three large muscles [that] connect the auricle [the outer ear] to the skull and scalp. These muscles, particularly the superior auricular muscle, exhibit increased activity during effortful listening tasks,” said first author Andreas Schroer of Saarland University in Germany.
For the study, 20 participants without any hearing problems were recruited and the electrical activity in their auricular muscles was recorded using electromyography as an audiobook along with distracting podcasts in front of or behind them was played.
“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,” the study highlighted.
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.
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Study findings
The study results implied that muscle might be involved in enhancing auditory perception under specific conditions, possibly by subtly adjusting the ear’s position to better capture sound.
The researchers stated that the findings could also help us understand or develop treatments for auditory processing disorders where such muscle activity could be either lacking or excessive.
“It could be worthwhile to explore auricular muscle activity to potentially be used as an objective metric to assess the effectiveness of hearing aid algorithms to reduce listening effort, as there is a clear physiological connection between the pinna and auditory perception.”
Although it is unknown why these muscles became vestigial over 25 million years ago, researchers posit that “evolutionary pressure to move the ears ceased because we became much more proficient with our visual and vocal systems”.