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Ear muscle we thought humans didn’t use — except for wiggling our ears — actually activates when people listen hard

Scientists have discovered that vestigial ear muscles – remnants from our distant evolutionary past – become surprisingly active when humans strain to listen in challenging environments. This finding reveals an unexpected link between our ancient past and modern listening behaviors, according to research published in Frontiers in Neuroscience.

The study, led by Andreas Schröer at Saarland University, focused on the auricular muscles, which once helped our ancestors move their ears to better capture sound. While these muscles became largely inactive in humans around 25 million years ago, the research shows they still respond to challenging listening situations.

“These muscles, particularly the superior auricular muscle, exhibit increased activity during effortful listening tasks,” said Schröer. “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.”

Using electromyography to measure muscle activity, researchers tested 20 participants with normal hearing in various listening scenarios. The participants attempted to follow an audiobook while competing podcasts played at different volumes from speakers positioned in front of or behind them.

The study revealed distinct responses from two different ear muscles. The posterior auricular muscles reacted to sound direction, while the superior auricular muscles activated more intensely during difficult listening conditions. This activity increased notably when participants reported struggling to follow the target audio.

However, the practical impact of this muscle activation remains unclear. “The ear movements that could be generated by the signals we have recorded are so minuscule that there is probably no perceivable benefit,” Schröer explained. “However, the auricle itself does contribute to our ability to localize sounds. So, our auriculomotor system probably tries its best after being vestigial for 25 million years, but does not achieve much.”

The research team designed three difficulty levels for the listening tasks. In the easiest condition, distracting sounds were quieter and distinctly different from the target audio. The most challenging scenario featured louder distractions that more closely matched the target sound’s characteristics. Participants’ self-reported effort levels and performance on comprehension tests aligned with the superior auricular muscles’ activity patterns.

Looking ahead, the researchers plan to expand their investigation. “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,” said Schröer. He added that studying these effects in people with hearing impairments would be particularly valuable.

This discovery could potentially lead to new ways of objectively measuring listening effort, which has traditionally relied heavily on subjective self-reporting. Such measurements could prove valuable for developing and evaluating hearing assistance technologies.


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