ear muscle activation focused listening

New Research Reveals Ear Muscle Activates During Focused Listening

The Role of Auricular Muscles in Hearing

Ancestral Function and Vestigial Structures

If you can move your ears, you're using muscles that helped our distant ancestors enhance their hearing. These auricular muscles would adjust the pinna's form, funneling sound waves directly to the eardrum.

Although our ancestors ceased relying on them millions of years ago, auricular muscles in humans remains as vestigial structures. However, recent research reveals that these muscles still activate when we focus on distinguishing competing sounds.

Insights from The Frontiers in Neuroscience Study

Andreas Schröer, first author of the Frontiers in Neuroscience study from Saarland University, explains that ear wiggling relies on three large muscles that connect the auricle to the skull and scalp.

These muscles, especially the superior auricular muscle, become more active during intense listening efforts, suggesting their role extends beyond reflexes to aiding attentional focus in challenging auditory conditions.

measuring Listening Effort

Electromyography and Auricular Muscle Activity

Quantifying listening effort remains difficult without self-reported measures. Yet, electromyography, which records muscle electrical activity, provides insight into auricular muscle function during attentive listening. Prior studies indicate that the posterior and superior auricular muscles—responsible for pulling the ears up and back—activate when an individual focuses on auditory stimuli. This suggests their ancestral role in pinna movement to optimize sound reception.

Hypotheses on Vestigial Function

"The exact caused of these muscles becoming vestigial remains unclear, given that our ancestors lost this function around 25 million years ago," Schröer noted. "A plausible hypothesis suggests that as human visual and vocal capabilities advanced, the selective pressure for ear mobility diminished."

Experimental Approach

Study Design and Conditions

Researchers examined whether auricular muscles exhibit heightened activity during complex listening conditions by enlisting 20 participants with no hearing impairments. Electrodes were affixed to their auricular muscles as they listened to an audiobook with distracting podcasts played from speakers positioned either in front or behind them. The experiment consisted of 12 five-minute trials, each varying in difficulty across three levels.

Adjusting Task Difficulty

In the Easiest Condition, the podcast was played at a lower volume than the audiobook with a clear distinction between the two voices. To increase difficulty researchers introduced a podcast that closely resembled the audiobook's tone and increased the volume of distracting audio. However, they ensured that even the most challenging condition remained achievable—if participants disengaged no physiological effort could be measured.

Participant Feedback and Comprehension

Following each trial, participants were asked to assess their listening effort and estimate how frequently they lost track of the audiobook. Additionally, researchers tested their comprehension through content-related questions.

Key Findings and Implications

Distinct Muscle Responses

The researchers observed that the two auricular muscles exhibited distinct responses to varying conditions. While the posterior auricular muscles were sensitive to shifts in sound direction, the superior auricular muscles showed greater activation in response to the task's level of difficulty.

Self-reported effort levels and the frequency with which participants lost track of the audiobook increased with the task's difficulty. Additionally, accuracy in answering content-related questions significantly declined as the moved from moderate to high difficulty.

Superior Auricular Muscle as a Measure of Listening Effort

This findings aligned with the activity levels of the superior auricular muscles, which did not show increased activation during the medium mode compared to the easy mode, but were notably active during the difficult mode. This indicates that superior auricular muscle activity may serve as an objective measure of listening effort, though it remains unclear whether this muscle activity aids in hearing.

Evolutionary Considerations

"The ear movements induced by the recorded signals are subtle that any potential benefits are likely imperceptible," said Schröer.

While the auricle plays a role in sound localization, the auriculomotor system likely exerts its best effort after 25 million years of vestigial development, though its effectiveness is limited.

Future Directions and Research Needs

Further Studies and Practical Applications

The researchers emphasized that additional studies are needed to validate these findings and explore their practical applications. Like many auditory studies, their sample size was limited, consisting mostly of young, healthy individuals. To draw more robust conclusions, larger and more diverse participant groups, tested under more realistic conditions, are required.

Exploring Additional Impacts on Hearing

Schrö er stated, "In the future, we aim to explore the potential impact of muscle strain and the ear's minute movements on sound transmission."

"It would also be valuable to examine how these factors affect individuals with hearing impairments."

Source

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