Johannes Zaar, Senior Scientist at Eriksholm Research Centre, is working in the field of speech processing and psychoacoustics. Johannes is now reaching a big milestone in his career as a key member of the team behind the ground-breaking ACT™ test.
In October 2023, Interacoustics launched the Audible Contrast Threshold (ACT) test at EUHA 2023 in Nuremberg, the international congress of hearing aid acousticians. The ACT test is a breakthrough hearing test that complements the pure-tone audiogram. Designed to predict hearing-in-noise ability with hearing aids, the ACT test marks the beginning of a new era of more precise and personalized hearing aid fitting and is already in use worldwide. The project is led by Interacoustics Research Unit (IRU) and the new test is born from collaboration with leading scientists around the world, including Johannes Zaar:
“It has been really rewarding to experience the interest. So far, the uptake has been good.”
A new type of hearing test
For the past 100 years, the pure-tone audiogram has been used as a diagnostic test to measure a person’s hearing thresholds across frequencies. In other words, the pure-tone audiogram captures the sound level needed for an individual to hear a tone at different frequencies. However, it does not reveal a person’s hearing ability in noise when the loss of audibility (captured by the audiogram) has been compensated by means of hearing-aid amplification. Consequently, individuals who struggle with their hearing in noise will not get a satisfactory diagnosis by relying solely on a pure-tone test:
“The audiogram does not tell us enough about hearing-in-noise ability. It is even possible that those who have a normal audiogram still have problems with their hearing. But it is hard to help if you can’t diagnose – now we have a tool to do that.”
With the introduction of the ACT test, hearing care providers have the means to predict the quality of a person’s hearing in the natural soundscapes of daily life. This allows a more precise fitting of the hearing aids, which then reduces the need for subsequent fitting and adjustments.
“Clearly something here”
The scientific foundation for the ACT test traces back to earlier studies on the Spectro-Temporal Modulation (STM) test which became the core of Johannes Zaar’s postdoctoral work.
After finishing his PhD on speech perception and computational auditory modelling at the Technical University of Denmark (DTU), Johannes stayed on for a year on a postdoc contract. At one point, he was approached by James Harte, who is now Senior Director at Eriksholm (Research Manager at IRU at the time) and Søren Laugesen, the current Research Manager at IRU, who pointed him towards promising research on the STM test. The STM test predicts how well people understand speech in noise with hearing aids on, but the latest study from (Bernstein et al. 2016) had some problems. It showed that for 1/3 of the test participants, the test was too hard to do.
Johannes was encouraged to do a postdoc in collaboration with DTU, IRU and Oticon. The aim was to make the STM test clinically viable and to validate its predictive power of speech-in-noise performance with hearing aids on, especially in realistic conditions. He was intrigued, and the project ran from 2017-2019.
“When I saw the strong relation between realistic speech-in-noise understanding with hearing aids on and the STM test result, I thought: there is clearly something here! In every study you get nervous about it. You worry that it’s a fluke. But in the end, I was confident about the execution, our methods and I had lots of support.”
The postdoc study showed clear and promising results, but still there were open questions. Would the test be feasible for actual clinical use?
Next phase: keeping it simple
In October 2019 Johannes took on a scientist position at Eriksholm Research Centre. For the first six months, he continued spending most of his time working on a follow-up project at IRU that would define the clinical version of the ACT test.
The goal was to make the test simple, quick, and easy to use for audiologists. The core team, which included Søren Laugesen (IRU), Lisbeth Birkelund Simonsen (IRU) and Raul Sanchez Lopez (now at Oticon), developed the basis for the ACT test. The basic setup of a pushbutton and a pair of headphones ensured an efficient and convenient method.
While the work continued at the IRU to finalize the test, Johannes was engaged in other projects at Eriksholm. In 2021 he worked with a new team consisting of Søren Laugesen (IRU), Sébastien Santurette (Oticon), Gary Jones (Oticon), Chiemi Tanaka (Demant Japan) and Marianna Vatti (Oticon). They initiated a large-scale project with external collaborators to validate the ACT test in German and Japanese language groups, ensuring its reliability and its predictive power over realistic speech understanding in hearing-impaired listeners with hearing aids. This study (Zaar et al., 2023) provided the evidence used for the launch in 2023.
“It is very satisfying to have come through as a team and see our work out there. We have not celebrated yet, but we certainly will.”
Now, the journey continues. Johannes says he is excited to see how the data from the ACT test can be used, and ultimately give us a more holistic understanding of hearing impairment.
Interested in learning more about Johannes Zaar and his work? View his employee portrait here.
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