Recently, Prof. Hugh McDermott, and inventor of the proprietary SoundRecover technology used in Phonak devices like Naída, was awarded the first Callier Prize from the University of Texas at Dallas, which was established to recognize individuals whose leadership has fostered scientific advances and significant developments in the diagnosis and treatment of communication disorders. The following is an excerpt of an interview Dr. Torsten Held, Scientific Marketing Manager at Phonak HQ, conducted with Prof. McDermott about his groundbreaking work.
First I would like to congratulate you on winning the first Callier Prize from the University of Texas at Dallas. Could you explain to us for which part of your extensive work the prize has been awarded?
The citation for the Callier Prize states that it has been established to "recognize individuals whose leadership has fostered scientific advances and significant developments in the diagnosis and treatment of communication disorders." I think the two main projects in which my research has benefited people with hearing loss are the development of improved sound-processing techniques for cochlear implants and the development of the SoundRecover frequency-compression scheme for Phonak hearing instruments.
Your formal education is in electronic engineering. Subsequently your PhD thesis was conducted in the field of cochlear implants: What sparked your interest in hearing disorders?
My father was a professional violinist and I grew up in a very musical family environment. As I was also interested in electronics from an early age, it seemed natural to combine those topics when I was looking for a suitable research area for my PhD. I was extremely fortunate to become involved in the development of the cochlear implant in Melbourne just when it was starting to show real promise for alleviating the most severe types of hearing loss.
Your work has not only benefited signal processing in CIs; specific sound processing schemes have been successfully implemented in HIs. Can you tell us something about that?
In our research group in Melbourne, we became concerned that there were some people whose hearing loss did not seem severe enough to justify cochlear implantation at that time, but who were also not receiving satisfactory performance from the acoustic hearing instruments that were available then. Because their problem was mainly with the perception of high-frequency components of sounds, we started a research project to address that problem in particular. This work led eventually to the development of the SoundRecover frequency-compression scheme that we carried out under contract to Phonak.
What are the advantages of frequency compression?
Frequency compression generally makes high-frequency sounds easier to hear and easier to discriminate. It achieves this without affecting lower frequencies and while avoiding the risk of over-amplification, even for people with a particularly severe hearing loss in the high frequencies.
Can frequency compression be adjusted to individual needs?
Yes, we always considered that there was unlikely to be a single way of compressing high frequencies that would suit every individual. In general, SoundRecover compresses a wider range of frequencies for people with a more extensive and/or more severe hearing loss. Fortunately, Phonak has devised a very simple and effective procedure for presetting the SoundRecover scheme based on the audiogram of the individual hearing-instrument user.
Which sounds in particular are perceived better with frequency compression?
In speech, the fricative consonants such as /s/ and /sh/ are often perceived more readily with frequency compression. Just as importantly, they are usually also made easier to discriminate. In addition to high-frequency components of speech, certain other sounds, such as birdsong and various environmental noises, can typically be heard better as well.
Is there a typical audiometric configuration that responds best to frequency compression or do you think people with different kinds of HL can profit?
It seems probable that almost anyone with a high-frequency hearing loss could potentially benefit from SoundRecover, although it depends on providing an appropriate fitting to each individual. In extreme cases, however, certain people, including those with a profound or total hearing loss across an extensive range of high frequencies, may require a cochlear implant.
Is there a potential benefit of FC for people with cochlear dead regions in the high frequency regions?
Initially we expected that having a high-frequency cochlear "dead region" would be a definite indication for frequency compression. While I think it is certainly true that many people with such dead regions are suitable candidates for frequency compression, the research has also shown that many people with high-frequency hearing loss but no evidence of extensive dead regions can also obtain benefit with frequency compression.
What can you say about the use of frequency compression in children with hearing loss?
There is already strong evidence that children as well as adults can benefit from frequency compression, provided that it is appropriately fitted. Benefits have been observed not only in sound perception but in speech production also.
Are there any obvious contraindications for the use of FC?
There are no specific contraindications of which I am aware. However, a small proportion of people who seem to have suitable types of hearing loss report that they prefer not to use frequency compression or that they experience no benefit with its use.
Modern hearing instruments with frequency compression can improve not only audibility but also speech production. Why is this?
It is much easier to learn to produce speech sounds accurately and consistently when those sounds are clearly audible and easy to distinguish. Because frequency compression enhances the perception of high-frequency sounds, including certain speech sounds, it is not surprising that speech production may also be improved.
What advantages other than improved hearing and speech production does frequency compression offer?
A strong benefit that we observed quite early in our research was reduction of feedback. The lowering of high-frequency sounds greatly reduces the likelihood that the amplification of the hearing instrument will result in any feedback oscillation (or whistling). In conventional hearing instruments, feedback is most often a problem at high frequencies when relatively high gains are required.
In which area of research do you expect the most immediate steps to improve current hearing care strategies?
I think the greatest potential may lie in combining acoustic and electric stimulation through the fitting of one or two acoustic hearing instruments as well as one or two cochlear implants to people with suitable types of hearing loss. There is a pressing need for further research to develop appropriate devices and fitting strategies. Ultimately, however, it seems likely that many people will choose to use such combined devices so that they can obtain the maximum perceptual benefit from each form of stimulation.
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