For 48 million Americans struggling with hearing loss, it can be difficult to follow conversations in noisy environments. Whether you’re at a restaurant, out for a night on the town, or in the workplace, it can be difficult to understand what is being said while having to filter out the background noise; a phenomenon called the “cocktail party effect”. However, this phenomenon doesn’t only affect the hard of hearing. Research has indicated that people with normal hearing can experience this same difficulty with little explanation until now. According to a new study led by researchers at Massachusetts Eye and Ear, they have discovered a pair of biomarkers of brain function that may help to explain why a person with healthy hearing may struggle to follow conversations in noisy environments, charting the path for next-generation clinical testing for hidden hearing loss (HHL).
Defined by the Biomarkers Definitions Working Group in 2001, Biomarkers are “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention”. For the brain, this means that biomarkers can be used to measure function and the molecular content of the brain through different measuring techniques. Previous research and techniques that the team from Massachusetts Eye and Ear has expanded to fit their unique research.
Knowing that HHL could not be measured by a regular audiogram, the study authors were motivated to develop objective biomarkers that might explain hidden hearing loss complaints, prompting them to develop two sets of tests. First, researchers would measure electrical EEG signals from the surface of the ear canal, capturing how effective the earliest stages of sound processing in the brain were at encoding subtle but rapid fluctuations in sound waves. Secondly, researchers utilized specialized glasses that measure changes in pupil diameter as subjects focused their attention on one speaker while others spoke in the background. Why pupil diameter? Past research has shown that changes in pupil size can reflect the amount of cognitive effort expended on a given task.
By combining the measurements of electrical EEG signals and changes in pupil diameter, researchers could identify which subjects struggled in noisy environments and which subjects showed no difficulty. These biomarkers were developed to represent “listening effort” and the “ability to process rapid changes in frequencies” and may help indicate whether a patient may be struggling with HHL.
Our study was driven by a desire to develop new types of tests,” stated study author Aravindakshan Parthasarathy, PhD., “Our work shows that measuring cognitive effort in addition to the initial stages of neural processing in the brain may explain how patients are able to separate one speaker from a crowd.” Considering that normal audiograms could not measure this difficulty as the developed biomarkers could, researchers from Massachusetts Eye and Ear are hopeful that their study will make a difference.
“Speech is one of the most complex sounds that we need to make sense of,” Dr. Polley said, ” “If our ability to converse in social settings is part of our hearing health, then the tests that are used have to go beyond the very first stages of hearing and more directly measure auditory processing in the brain.”
If you are struggling with hidden hearing loss symptoms, speak to a hearing health professional to receive medical advice about treatment options or tips to help you in noisy environments.