Extending hearing aid testing beyond the walls of the sound booth

Raise your hand if you’ve ever heard the following statement from a patient: “I hear fine in the audiology office, but things are different in the real world.” I’m sensing a lot of hand-raising out there.

As a clinical audiologist this was something I heard from patients almost every single day. This idea of achieving a hearing aid fitting that must transcend the confines of a quiet audiologist office continues to be a challenge. It is well-understood that listening in a quiet audiologist office, even with the introduction of background noise through a soundfield speaker (oftentimes the best-case scenario), cannot replicate real-world experiences. If time allows and the audiologist is able to test the hearing aids in a more complex environment, like a listening booth with an array of speakers, it still doesn’t capture the dynamic nature of real-world listening.

Replicating the real-world listening experience

We ran into a similar problem when testing hearing aids here at the Phonak Audiology Research Center. What we know to be true about listening in the real world is that it IS challenging, diverse, and typically the most difficult listening combines both reverberation and background noise. How do we replicate these characteristics of real-world listening in a clinical environment? Well, the truth is that at this point, we really can’t. Advancements in virtual reality, 3D listening environments, and other technological innovations have made it a smaller leap between lab testing of hearing aids and actual real-world listening, but these systems are still very complex and may still not fully capture “a day in the life” of a hearing aid user.

The Phonak Audiology Research Center believes that real-world testing is an essential element to understanding how hearing aids are performing. Testing in a well-controlled sound booth is the “gold standard” in terms of research design and replicability. We know, however, that as internal control increases, the ability to generalize performance to the real world decreases. That is why at PARC we focus on research in both highly-controlled research environments, but also recognize the importance of testing in the real-world. Both are essential to understand hearing aid performance.

The Listening Loft, a reverberant room in the PARC designed to look and feel like the first floor of a home or an apartment, provides one such example of how the real world can be brought into the research environment. This space allows for hearing aid users to provide feedback and complete performance testing in a reverberant space, layering elements like a TV playing in the background and speech from a distance- both of which cannot be assessed easily in a sound booth.

Real-world testing in changing environments

The quintessential example of real-world listening in the context of a research study was the AutoSense OS investigation here at PARC (see link for more information about the study design and results). AutoSense OS is the automatic operating system in Phonak hearing aids. The idea of real-world testing was particularly relevant for this study because assessing an entire operating system requires not only understanding performance in static environments, or in one environment, but in constantly-changing environments. We assessed speech understanding of participants in AutoSense OS compared to a fixed, manual program, and compared to competitor devices in a variety of settings: the Listening Loft (mentioned above), a local coffee shop, and in the car. Yes, it was fun to be out and about with the research participants, but even more than that, this study helped us truly understand how the hearing aids are performing where it really matters. I believe this study continues to be the PARC study everyone remembers and loves to talk about because of its real-world application and accessibility.

I would be remiss to not mention the fact there has been some criticism or skepticism that comes along with this type of “real-world” research. As researchers, ourselves, we are fully aware of the limitations and challenges that come along with designing research studies in the real world. We design these studies with the utmost care to minimize the introduction of variability between subjects. For example, it was essential when testing in the car that we used a.) the same car for all participants, b.) travelled at the same speed, c.) kept the air conditioner settings consistent and d.) never tested when it was raining due to added background noise. In the coffee shop we consistently measured the level of background noise to ensure all participants received the same degree of difficulty for testing. These measures were put in place to maintain as much consistency as possible.

The other message for any skeptics is that this is not the only type of research we do at PARC. In fact, the study described above was only one piece of our research done on AutoSense OS. This real-world testing is one element, in addition to highly-controlled testing in the sound booth and technical measurements using KEMAR, our acoustic mannequin. Together, all these elements give us a rich and full context of how the hearing aids are performing in both idealized situations and real-world situations.

Real-world assessments in the most relevant environments

Our next venture into real-world assessment of hearing aids is with Ecological Momentary Assessment (EMA). Conducted on a smartphone, the phone prompts the hearing aid user to answer a questionnaire based on acoustics in the environment, in real time. For example, the hearing aid user could be prompted to answer a questionnaire when the background noise level is at a certain volume, or when the environment reaches a particular signal-to-noise ratio. This allows for extremely specific and accurate assessment of the hearing aids in the most relevant environments.

We truly believe that testing hearing aids in real world environments is an extremely important aspect to the investigation of hearing aids. Testing in the sound booth is, and always will be an aspect to the testing here at PARC, but extending beyond the walls of the sound booth provides the true-to-life aspects of hearing aid performance.

We invite you to read a previous blog post by Lori Rakita describing her work as a research audiologist at the Phonak Audiology Research Center. And if you would like to learn more about Lori and her work at PARC, a recent interview was published in AudiologyOnline.