By Viji Easwar, Ph.D.
Measuring neural responses to sound is the only way to assess how well a baby, too young to do hearing tests, can hear. Significant strides have been made to use neural responses to diagnose hearing loss severity and type in babies as young as 2 to 3 months of age.
However, there are limited clinical tools to assess how babies with hearing loss, often fitted with hearing aids within 3 months of age, hear speech with hearing aids. It is critically important to ensure that hearing aids have adequately restored hearing during rapid brain development within the first 6 months of life, to facilitate speech perception and later language development.
Over the past decade, we have been working on a neural test that can measure how a listener hears important speech sounds with and without hearing aids. The test plays the word “susashee” or its shorter versions like “sushee” and measures neural responses tagged to each speech sound. The sounds are chosen and modified to test access to a range of frequencies (heard as pitch) that are essential for good speech understanding, and speech and language development.
Spectrogram of the token /su∫i/. Credit: Easwar et al./Trends in Hearing
Our previous work has shown that such a neural test is useful to assess access to speech in adults with hearing loss using hearing aids (2015), can be measured in babies in their sleep (2021), and is equally accurate in 5- to 17-year-old children with typical hearing (2022).
In our most recent study published in the January-February 2023 issue of the journal Trends in Hearing, we assessed whether the neural test could predict hearing aid benefit in 5- to 17-year-old children with permanent hearing loss. Our results demonstrated that neural responses were sensitive to the improved audibility provided by hearing aids; they were stronger with than without the amplification provided by hearing aids. Further, the improvement in speech understanding with the use of hearing aids was reflected in the degree to which neural responses improved with the use of hearing aids.
Following these successful results, we are now working toward utilizing additional, higher order brain processes in order to improve accuracy and speed of the testing and to improve clinical viability in babies with hearing loss.
A 2019 Emerging Research Grants scientist funded by the Children’s Hearing Institute, Viji Easwar, Ph.D., is the lead researcher of the pediatric hearing research program at the National Acoustic Laboratories in Sydney, Australia. She shared what receiving the Emerging Research Grant meant to her career in our Fall 2022 issue of Hearing Health magazine.
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Babies are too young to do hearing tests until 8 to 10 months of age, and at such young ages, tracking brain waves to sounds is the only reliable way to assess hearing.