Three large muscles long thought to be vestigial do apparently engage when we listen. A study published in the journal Frontiers in Neuroscience has established that the muscles, particularly the superior auricular muscle, exhibit increased activity during effortful listening tasks, and not merely as a reflex.

In challenging auditory situations, we try to use these muscles as many animals do – such as our primate ancestors – to funnel sound to our auditory system. There is no suggestion from this research that we are doing much more than making monkeys of ourselves.

Listening effort is a key part of modern hearing science and manufacturers’ experts seek design and technology elements in hearing aids precisely to reduce toil for our brains. But this successful attempt to show that humans still use auricular muscles – or try to – is unlikely to generate too much excitement among researchers in hearing aid labs: the researchers found no indication that the muscles might today be strong enough to bring a listening benefit, and the posterior auricular muscle, which is the second largest, did not show increased activity during effortful listening, suggesting that any potential pinna movement would be severely limited.

 

A useful measurement tool for hearing aid effectiveness?

 

The study may, nevertheless, have implications for testing. One of the conclusions of the published paper suggests “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”.

In addition, the activity of auricular muscles as an objective correlate for effortful listening could be useful in human-machine interaction by monitoring the state of the user, especially because placing sensors around the ear can be done in a very unobtrusive manner.

 

A listening experiment using difficult sound environments

 

To test their hypothesis, the scientists, mostly from Saarland University in Germany, attached electrodes to the sides of people’s heads, and asked them to listen closely to an audiobook. Different challenge modes were imposed, with the sound coming from different angles, and other competing sounds.  It was found that the more difficult it was for participants to hear the audiobook, the more the superior auricular muscles activated, as if participants were trying to prick up their ears like a dog or cat.

Some people use these muscles to generate a wiggle of the ears. The ear wiggle was one of the best-known visual gags used by the English comedian Stan Laurel in his films with Oliver Hardy. Even if the talented Laurel was able to wiggle his ears, the hilarious efforts seen on screen were the result of hidden lines or camera tricks.

 

 

We often use the term “straining your ears”, a figure of speech suggesting a muscular effort. This muscular involvement, explained the study’s first author, Andreas Schröer, was an ability our ancestors lost around 25 million years ago. “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,” said Schröer.

“The ear movements that could be generated by the signals we have recorded are so minuscule that there is probably no perceivable benefit. 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,” added the lead researcher.

The scientists pointed out that more work will be necessary to confirm these results and develop practical applications. Like many hearing studies, their sample was relatively small and composed of young people without hearing problems. Larger, more diverse participant groups, in more realistic conditions, are needed.

Source: Frontiers/Frontiers in Neuroscience