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Muscles that facilitated our distant ancestors’ attentive listening can be utilized if one is able to move their ears. The pinna was reshaped by these auricular muscles, which facilitated the passage of sound to the eardrums.
Our ancestors ceased the use of auricular muscles millions of years ago, which is why they are only vestigial in humans. However, scientists who are currently investigating the functionality of these muscles have discovered that they activate when we attempt to listen to competing sounds.
The auricle is connected to the the skull and scalp by three crucial muscles that are necessary for the act of ear wiggling.
The superior auricular muscle, in particular, is more active during tasks that require effortful listening. This indicates that these muscles are activated not only as a reflex, but also as a potential component of an attentional effort mechanism, particularly in auditory environments that are exceedingly difficult.
It is challenging to evaluate the extent to which an individual is attentive without the use of self-reported metrics. However, electromyography, which quantifies the electrical activity of a muscle, can assist in the identification of movement of the auricular muscles that are associated with attentive listening.
The largest muscles, the posterior and superior auricular muscles, have already been demonstrated to respond during attentive listening in similar research. This is because they are believed to have been involved in the movement of the pinna to capture sounds, as they draw the ears up and back.
It is challenging to determine the precise reason for these becoming vestigial, as our ancestors lost this capacity approximately 25 million years ago. A possible reason is that the evolutionary stimulus to move the ears diminished as we became more adept at using our visual and vocal systems.
In order to determine whether these muscles are more activated during difficult auditory tasks, the researchers recruited 20 individuals who did not have hearing problems. They attached electrodes to the auricular muscles of the participants and subsequently played them an audiobook and distracting podcasts from speakers located either in front of or behind them. Participants were subjected to twelve five-minute trials, each of which encompassed three distinct levels of difficulty.
During the study, the researchers discovered that the two auricular muscles responded differentially to the various conditions. The superior auricular muscles responded to the task’s difficulty level, while the posterior auricular muscles responded to variations in direction.
The accuracy of the participants’ responses to queries about the audiobook decreased significantly between the medium and the difficult mode, and their self-reported measures of effort and the frequency with which they lost track of the audiobook increased in accordance with the difficulty of the task.
This was in accordance with the activity levels of the superior auricular muscles: they were less active during the medium mode than during the easy mode, but they were highly active during the difficult mode. This implies that the superior auricular muscles’ activity could serve as an objective indicator of listening exertion, although it is uncertain whether the muscle activity aids in hearing.
The auditory movements that could be produced by the signals the researchers have recorded are so minimal that there is likely no discernible advantage.
Nevertheless, the auricle itself does play a role in our capacity to identify sounds. Therefore, the auriculomotor system likely makes an effort to function at its best after staying vestigial for 25 million years, but it fails to achieve much.
In the future, the researchers intend to investigate the potential impact of muscle tension or the ear’s minute movements on sound transmission.
It would also be intriguing to examine the impact of these factors on individuals with hearing difficulties.
Sources:
Electromyographic Correlates of Effortful Listening in the Vestigial Auriculomotor System, Frontiers in Neuroscience (2025). DOI: 10.3389/fnins.2024.1462507
https://phys.org/news/2025-01-ear-muscle-thought-humans-didnt.html
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