Hair cells are sensory receptors that move in response to sound waves, triggering an electrical impulse that is sent to the brain's cerebral cortex.
Pandemic Discovery

Hearing one among many

A pair of biomarkers of brain function may help explain why some people with normal hearing struggle to follow conversations in noisy environments, says a team of HMS researchers at Massachusetts Eye and Ear. One biomarker represents listening effort, and the other measures the ability to process rapid changes in frequencies.

This hearing difficulty, known as hidden hearing loss, refers to listening difficulties thought to arise from abnormal connectivity and communication of nerve cells in the brain and ear. Conventional hearing tests do not  detect neural changes that interfere with how we process sounds at louder levels.

In an effort to detect hidden hearing loss, the researchers developed two sets of tests that they administered to a small group of young and middle-aged individuals with clinically normal hearing. One test measured electrical signals from the surface of the ear canal to capture how well the earliest stages of sound processing by the brain were encoding subtle but rapid fluctuations in sound waves. For the second test, participants wore specialized glasses that could measure changes in pupil diameter as they focused their attention on one speaker while others babbled in the background. Previous research showed that changes in pupil size can reflect the amount of cognitive effort expended on a task.

When the researchers combined the measures of ear canal EEG with changes in pupil diameter, they were able to identify which participants struggled to follow speech in a noisy setting and which didn’t. Conventional testing could not account for either of these performance differences.

Parthasarathy A et al., eLife, January 2020

Image: Henning Horn, Brian Burke and Colin Stewart, Institute of Medical Biology, Agency for Science, Technology, and Research, Singapore; courtesy of the U.S. National Institutes of Health.