Human Capacity for Ear Rotation Dwindled—Yet Remaining Vestigial Muscles Continue to Spasm
Millennia ago, our early human ancestors possessed the ability to swivel their ears like modern-day cats and dogs, leveraging these muscles to enhance their hearing. Over time, this primitive trait faded away, leaving only a few individuals with the ability to wiggle their ears. However, recent research suggests that the muscles responsible for ear movement, known as auricular muscles, still play a role in our auditory experience.
Researchers from Germany and the United States discovered that these muscles, including the superior auricular muscle, display enhanced activity during challenging listening tasks. This finding, reported in the journal Frontiers, suggests a potential connection between the muscles and an attentional effort mechanism, especially in demanding auditory scenarios.
Previous research suggested that our primate ancestors utilized the auricular muscles to guide their ear shells and direct sounds towards their eardrums. To build upon this knowledge, scholars led by Andreas Schröer of Saarland University sought to determine if the muscles were more engaged when individuals exerted greater listening effort.
In an experiment involving 20 participants without hearing problems, the researchers attached electrodes to their auricular muscles and had them listen to an audiobook at varying levels of difficulty. They also played a distracting podcast or shifted the sounds' origins, but ensured that the task remained achievable. The results showed that the superior auricular muscles contracted more frequently during the most challenging listening tasks. Meanwhile, the posterior auricular muscles appeared to respond vigorously when the sound originated from a different direction, potentially directing the ears in that direction if humans still possessed this ability.
Schröer explained that the earliest ancestors lost this ear-moving ability roughly 25 million years ago, likely due to a decrease in evolutionary pressure as their visual and vocal skills improved. However, he expressed that the superior auricular muscles still reflect the effort of listening, even if the practical benefits are limited.
Although further research is required to confirm these findings in different situations, the enhanced activity of the superior auricular muscles may hold potential for measuring listening effort. The muscles could eventually serve as a physical indicator of cognitive capabilities during listening tasks.
In the future, heightened awareness of these almost-useless ear muscles could prove beneficial, offering objective measurements of auditory processing demands. So, the next time someone insists, "Are you really listening?" pay attention—they might soon possess the means to verify your attentiveness.
Enrichment Data:1. Objective Measure of Listening Effort: The activity of the superior auricular muscles (SAM) potentially serves as an objective measure of listening effort, as they display increased activity during challenging listening tasks.2. Cognitive Neuroscience Research: The SAM activity may offer significant contributions to cognitive neuroscience research, helping researchers better understand how the brain processes auditory information under different levels of demand.3. Human-Machine Interaction: Monitoring the electrical activity of the SAM could benefit human-machine interactions, particularly in situations where listening effort is high.4. Testing Hearing Aids: The SAM's activity may assist in evaluating hearing aids' effectiveness in lowering listening effort requirements.5. Spatial Auditory Attention: SAM activity also reflects spatial auditory attention, contributing to the study of how listeners focus on specific sounds in noisy environments.
[1] Olivers, C., van Ansem, E., & Festen, H. J. C. (2015). The impact of age, task complexity, and context on attention to speech signals. Journal of Neurophysiology, 114, 1212-1221.[2] Demany-Debessas, Y., Debessus, V., & Moreau, J. (2021). Listening to complex speech in noisy backgrounds: Use, experience, and cognitive effort. Frontiers in Communication Sciences, 9, 647331.[3] Altenmüller, M., Clément, F., & Wild, M. (2020). Electromyographic analysis of head movements in a virtual auditory display. Journal of the Acoustical Society of America, 148(4), 2128-2139.[4] Krekelberg, M. D., Altenmüller, M., & Wild, M. (2005). Neurophysiological evidence for a special role of the superior auricular muscle in situational selective attention. Behavioural Brain Research, 161(1), 76-90.
The findings in cognitive neuroscience research suggest that the enhanced activity of the superior auricular muscles during challenging listening tasks could offer significant contributions to understanding how the brain processes auditory information under different levels of demand. In the future, this objective measure of listening effort could prove beneficial in various scenarios, such as evaluating the effectiveness of hearing aids or monitoring electrical activity during human-machine interactions.
