The science of sound: Understanding how the brain helps us hear in noise

For millions of people worldwide, hearing loss is not simply a matter of volume but clarity—especially in noisy environments. Struggling to distinguish a single voice in a crowded restaurant, a busy office or even a family gathering is a common report among those with hearing difficulties. Researchers at the forefront of auditory science are investigating an essential but often overlooked aspect of hearing: the brain’s role in processing sound.

A study led by Department of Speech and Hearing Science Associate Professor Ian Mertes, titled “Olivocochlear Efferent Function: Associations with Hearing in Noise and Listening Effort,” aims to deepen our understanding of how the brain influences our ability to distinguish speech amid background noise. The project, supported by a three-year, $570,000 grant from the National Institutes of Health, will examine the neurological mechanisms that contribute to hearing in noise and the effort required to listen under challenging conditions.

Mertes has been interested in how the brain influences the inner ear since he was a graduate student.

Hearing is often thought of as a passive process: sound waves enter the ear, are converted into neural signals, and are sent to the brain for interpretation. However, the reality is far more complex. The auditory system has a top-down control mechanism that influences how the ear processes incoming sounds. This system, known as the medial olivocochlear efferent system, acts as a neural feedback loop that modulates auditory input.

But Mertes said there are still unanswered questions about how this system contributes to listening in everyday life. Efferent pathways originate in the brainstem and extend to the cochlea, the inner ear’s sensory organ responsible for converting sound waves into electrical signals. These pathways play a crucial role in adjusting how we hear in noisy environments. By selectively dampening background noise and enhancing speech signals, the medial olivocochlear system may improve our ability to focus on important sounds while ignoring irrelevant ones.

“My study also examines if the medial olivocochlear reflex is involved in listening effort,” he said. “Even if the medial olivocochlear reflex does not improve someone’s performance on a speech-in-noise task, it may reduce the mental resources needed to listen in background noise.”

Investigating Speech-in-Noise Recognition

The study aims to explore how variations in this top-down control contribute to an individual’s ability to understand speech in noisy settings. Researchers will work with adults who report varying levels of difficulty in hearing amid background noise. By measuring their auditory responses under controlled conditions, the team hopes to uncover patterns that link efferent function to speech recognition abilities. Mertes said that in addition to people with hearing loss, it’s estimated that up to 44 million U.S. adults have clinically normal hearing and yet report that they have difficulty hearing in noisy situations. 

“We are still trying to understand the underlying reasons for these difficulties,” he said.

Participants will undergo a series of tests assessing their ability to discern speech against different levels of background noise. These assessments will be paired with physiological measurements of inner ear and auditory brainstem activity, allowing the researchers to determine how the brain’s feedback mechanisms influence perception. By comparing individuals with and without self-reported hearing difficulties, the research team aims to identify specific deficits in the olivocochlear system that may contribute to these challenges.

“We hypothesize that medial olivocochlear reflex function will be reduced in the group that reports having significant difficulties because they have less noise reduction happening at the level of their inner ear,” Mertes said.

Measuring Listening Effort

Beyond understanding speech in noise, the study will also explore the cognitive effort required to listen in difficult auditory environments. Listening effort is a critical but often subjective aspect of hearing. Even if two individuals achieve similar results on a hearing test, one may expend significantly more mental energy to achieve the same level of comprehension.

Implications for Future Research and Interventions

The findings from this study could have significant implications for hearing health care. Currently, hearing aids and assistive devices primarily amplify sound, but they do not always enhance speech clarity in noisy environments. By better understanding the brain’s role in modulating auditory input, researchers may pave the way for new treatments or hearing aid technologies that target neural mechanisms rather than just the mechanical aspects of hearing loss.

For example, future hearing aids might be designed to simulate the brain’s natural medial olivocochlear efferent control system, selectively amplifying relevant sounds while suppressing background noise more effectively. Additionally, clinicians could use diagnostic tests based on medial olivocochlear efferent function to personalize treatment strategies, ensuring that interventions are tailored to an individual’s specific auditory processing profile.

A Step Toward Better Hearing Solutions

This study represents an important step in bridging the gap between neuroscience and audiology. By shedding light on the intricate relationship between the brain and the ear, researchers hope to improve outcomes for individuals struggling with speech-in-noise recognition.

“I’m currently focused on understanding the physiology that is involved in hearing in background noise,” Mertes said. “I’m hopeful that my work will help contribute to improved diagnosis and treatment of listening difficulties, especially for people with clinically normal hearing.”

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