Dr. Pamela Souza explains why evidence-based practices that work for mild to moderate degrees of hearing loss sometimes fail when applied to severe to profound hearing loss . . . and what you can do about it.
There is no question that hearing aids work.
The days when listeners had to repeatedly adjust their linear hearing aid volume to achieve comfortable loudness are behind us.
We now have sophisticated digital technology capable of providing audible signals across a range of input levels, improving the signal-to-noise ratio in most situations, and self-adjusting to the talker and the spatial environment.
Listeners with mild-to-moderate hearing aids are largely satisfied with their hearing aids. But severe to profound hearing loss (let’s call this S2P) is just…different.
Patients with S2P loss are less satisfied, on average, with their hearing aids. And among the many research studies which can inform hearing aid selection and fitting, very few have focused on listeners with S2P loss.
Why is this group different?
The starting point to answer that question is to think about the etiology of hearing loss.
- Mild-to-moderate loss is commonly associated with aging, noise exposure, or some combination of the two. Both age-related hearing loss and many noise-induced hearing losses occur over a period of time, with greatest threshold changes in the high frequencies. In contrast, S2P loss occurs during different points in life (from congenital hearing loss to gradual or sudden onset as an adult), and with varied etiologies and audiometric configurations.
- It’s likely that your patients with S2P loss are much less like each other – audiometrically speaking – than a group of patients with mild-to-moderate loss. Severe loss, in general, means greater loss of both inner and outer hair cells, greater likelihood of cochlear dead regions, and more loss of auditory nerve fibers, as well as a smaller dynamic range—all things that may result in distorted or poorly resolved speech even when that speech is audible.
Is this true for hearing aids?
Yes and no.
Some hearing aid features that were developed and tested for listeners with mild-moderate loss should, and do, work well for listeners with S2P loss. But there are also important differences to consider.
My suggestion is to think first about hearing abilities and communication needs, then connect those abilities and needs to the choice of hearing aids and assistive technology.
What are hearing aids doing really well?
Nearly all hearing aids use multichannel wide-dynamic range compression, which is is an excellent tool to manage audibility and loudness comfort for listeners with a small dynamic range.
Advances in feedback and noise management have also been very effective for listeners with S2P loss. Active feedback suppression can be particularly useful in cases where passive feedback management limits the ability to provide the desired gain.
Nearly all listeners with S2P loss report difficulty communicating in background noise, so adaptive directional microphones or binaural adaptive directionality are needed. (Remember to counsel the wearer about positioning relative to sound/noise sources to get greatest advantage from the hearing aid directionality.)
And wireless remote microphones have more options and seamless integration with hearing aids than ever before.
What could be improved?
Much of the clinical evidence on benefit of hearing aid features for S2P loss is based on small numbers of listeners or extrapolated from listeners with mild-to-moderate loss, so more studies are needed.
In the meantime, careful and consistent use of real-ear measures can help guide the choice of hearing aid parameters, started with frequency-gain settings.
A recent study of S2P candidates for cochlear implants1 found that only 29% of their hearing aids met NAL-NL targets for conversational speech – a reminder that the first fitting goal should be appropriate speech audibility.
However, more is not always better.
Because listeners with S2P loss are likely to have poorer fine-grained spectral discrimination and to rely more heavily on other cues, such as the speech envelope, some amplification strategies are designed to preserve envelope information.
Even without intentional envelope preservation, available data suggest we should avoid high compression ratios coupled with fast compression time constants, or use aggressive frequency lowering parameters in an effort to “squash” all of the aided speech signal into the listeners’ dynamic range.
Use what you need, verify aided output, and take the wearer’s reported experience into account.
Noise management is important, not least because listeners with severe loss report significantly poorer ability to hold a conversation in noise than listeners with mild-to-moderate loss.2 Adaptive directionality is effective and convenient, and can improve speech recognition at least in environments with low or moderate levels of environmental noise.
For noisier environments, such as restaurants, remote microphones offer more benefit, but practice surveys suggest that remote microphones are underused for adults with S2P loss. These are one of the most effective ways to improve signal-to-noise ratio, and should be discussed with every S2P patient.
And don’t forget about earmolds! Listeners with S2P loss should have custom earmolds rather than non-custom, ‘dome’ tips.
Considering the complex effects of S2P loss, we’re not likely to achieve perfect speech recognition even with the best hearing aids. But by listening carefully to patient needs and experiences and making thoughtful technology choices, we can get closer to optimal hearing treatment for all patients.
To learn more on the clinical management for those with severe and profound hearing loss, we recommend you read the full text of the recent publication available through Open Access in Seminars in Hearing, Guidelines for Best Practice in the Audiological Management of Adults with Severe and Profound Hearing Loss.
Dr. Pamela Souza featured in podcast series
The podcast, ‘The Audiologist’ launched a series based on content in the severe and profound guidelines. It delivers informative interviews with the experts who created them. Dr. Pamela Souza is one of the experts featured.
Find the series here.
- Holder, J. T., Reynolds, S. M., Sunderhaus, L. W., & Gifford, R. H. (2018). Current profile of adults presenting for preoperative cochlear implant evaluation. Trends in Hearing, 22, 2331216518755288.
- Souza, P., Hoover, E., Blackburn, M., & Gallun, F. J. (2018). The characteristics of adults with severe hearing loss. Journal of the American Academy of Audiology, 29, 764-779.