Open Fits, Pediatric Audiology, Noise Reduction and More: Interview with Harvey Dillon, PhD
Douglas L. Beck, AuD, spoke with Dr. Dillon in this first part of two interviews. They discussed adaptive noise reduction, frequency-lowering, dead regions, spatial processing disorders, super directional microphones, and more.
Academy: Good morning, Harvey. Thanks very much for your time today!
Dillon: Hi, Doug. My pleasure. Always nice to chat with you.
Academy: Harvey, if you don't mind, as your new book covers so many areas relating to hearing aids and amplification, and as I have at least one question relating to each of the 610 or so pages, we'll do this interview in two parts!
Dillon: Okay, very good. Let's do it.
Academy: So as best I recall, the first edition was extraordinarily thorough and was published in 2001—and it was tremendously successful. What occurred in the industry and the profession that inspired you to publish the second edition 11 years later?
Dillon: Yes, well…good question! I think the first edition was reasonably thorough, but so many things have changed. Perhaps the most significant change has been the widespread use and acceptance of open-fit hearing aids. Admittedly, I did mention open fits in the first edition, but it was not very prominent at that time. Of course, directional microphones are more widespread now than they were in 2001, and so that's been updated and revised. We now have more non-linear signal processing schemes than ever, and so that topic required a fresh new chapter. Of course, there are also some new and unique amplification alternatives such as middle-ear and bone-anchored implants and so that's required a fresh perspective as well.
Academy: Fair enough. And I should mention each of the 17 chapters is either new or has been revised, some more and some less, but they've each been updated to reflect the state-of-the-art, such that it is in 2012. Let me spend a moment listing abbreviated chapter titles so as to give the reader a better overview of the content: Introduction, Hearing Aid Components, Hearing Aid Systems, Electroacoustic Issues, Earmolds, Compression Systems, Directional Mics and Arrays, Advanced Signal Processing, Assessing Candidacy, Prescribing Amplification, Selecting-Adjusting and Verifying, Problem Solving & Fine Tuning, Patient Education & Counseling, Assessing Outcomes, Binaural & Bilateral Issues, Special Issues for Children, CROS-Bone Conduction, and Implanted Hearing Aids.
Dillon: Thanks, Doug.
Academy: My pleasure. Now then, as starting at the beginning is always nice and very predictable, let's jump around a bit. The first chapter I actually read was Chapter 16, "Special Hearing Aid Issues for Children." Let me admit that my single favorite pediatric audiology book is the 2008 book titled Pediatric Audiology – Diagnosis, Technology and Management by my dear friends Jane Madell and Carol Flexer. Chapter 18 in that book ("Hearing Aids for Infants and Children") was written by you and your colleagues (Teresa Ching and Maryanne Golding), and the three of you boldly went where few dared to tread!
That is, you stated (more or less) that modern hearing aid technology is so good that audiologists and dispensers should use noise reduction and directional microphones for children of all ages—just like adults! That was a very important declaration for many reasons, not the least of which was that it came from you and your co-authors, not from a hearing aid manufacturer! I believe many pediatric audiologists will read those words from four years ago and will be shocked! Have I encapsulated your thoughts accurately and do you still believe the same?
Dillon: Yes. You presented it succinctly and correctly and I still stand by those remarks. I know many pediatric audiologists do not believe these things, but let me just refer them to the book you mentioned and invite them to read the entire chapter and review the content in-depth. I also cover these topics in new edition of Hearing Aids, of course.
Academy: Okay, fair enough. It seems to me that beyond the issue of "believing" or "not believing" is a very real and problematic issue. Specifically, we simply cannot do scientific experiments on real children. That is, we cannot give a control group of 5- to 10-year-old children with hearing loss a "no noise reduction" and "no adaptive directionality" hearing-aid fitting, and then do the exact opposite for an experimental group of children, and then re-evaluate them at 12, 24, and 36 months to see which children have done best! That would not pass an IRB panel, it would have terrific ethical implications, and regardless of the outcome, it would need to be replicated…and on and on. So we have to make some reasonable assumptions and extrapolations…do you agree?
Dillon: Partly. It is certainly unethical to contrast an experimental versus a control group once we are already sure that one form of treatment is better than the other. However, it is reasonable and ethical when there is disagreement amongst informed, reasonable people about what is best. This may still be the case for directional microphones in young children even though I have made up my mind.
A bigger problem is the immense size of the study that would be needed, because of the many other factors that have large effects on the outcomes achieved. In the absence of such studies, however, once we have demonstrated, explored, and statistically and clinically proven that a particular technology works well and is beneficial for adults, we should fit that to children, too, unless there are sound reasons for not doing so. Unfortunately, the profession seems to have taken the opposite stand, which is "let's not do anything for children until and unless it's proven beneficial with children, because children are different." They are different in some ways, but that does not automatically imply that what is good for hearing impaired adults is not good for them.
Academy: Well, children are different, indeed. However, I think time is supporting the position you've taken and to underscore your point, imagine if we were to apply the "do nothing until proven safe" philosophy across all health and medical disciplines. We wouldn't fit eyeglasses, dental prosthetics or artificial limbs on children until formal scientific studies were performed involving control and experimental groups to document the benefit—but I think it's fair to say the benefits of these devices and protocols are intuitive and the actual studies cannot be performed, regardless.
Dillon: Yes, that's right. Further, a recent study that supports our position comes from Arizona State University. The study showed that adaptive noise reduction improved word learning rates in older children, and at least did no harm for younger children (Pittman, 2011). To me it's a defensible position to say that if the technology has proven to be beneficial in adults, we should assume it's good for children—unless it's proven to be contrary, or at least there is a soundly constructed argument as to why a contrary result should apply to children.
Academy: Harvey, another topic you address in the book which has enormous importance today is the issue of frequency lowering through whatever means (compression, transposition, etc.). Can you please tell me your thoughts on frequency lowering in 2012?
Dillon: Sure thing. And, I want to say that this topic was the most difficult topic I addressed in the book with regard to reviewing the data and drawing a conclusion from them! And so, there have been lots of experiments on frequency lowering, perhaps for some 30 or 40 years now. Unfortunately, the biggest consistency has been the inconsistency of the results. Unquestionably, there are some people who have received benefit from frequency lowering, and some who have not, but we don't know how to select who will do well and who will not, and we don't have any significant evidence that one frequency lowering technology is better than another.
One thing frequency lowering does offer is feedback reduction, and I believe some of the manufacturers are using frequency lowering to accomplish that goal, which is beneficial, but perhaps not the primary goal of frequency lowering.
Academy: And so I wonder if we're at that point where many people have jumped on the bandwagon, which encourages more people to do the same based on single subject studies, case reports, anecdotal information and so in, but the scientific evidence just isn't there? This discussion actually reminds me of the "dead zones" (i.e., dead regions) discussion.
That is, for some 10 years now, some clinicians have been testing and looking for dead zones, and the premise has been that if you find a dead zone, you should not fit high frequency amplification in that spectral zone. The only thing is that Robin Cox and her colleagues published a fantastic paper in 2011 (Cox et al, 2011) which pretty much disproved, or very seriously questioned all of that. In fact, the people in her study who were proven to have dead zones did better when they were given high-frequency amplification, than when it was withheld.
Dillon: Yes, well now you've selected the second hardest topic I addressed in the book! That was a wonderful, extensive study and it does remind us that we need science to verify and validate our assumptions and initial findings. To me, although there are clearly people with dead zones and these can't be predicted completely from the audiogram, there is still considerable uncertainty as to whether the prescription needs to be modified if it is known they are present. Consequently, I don't think it's worth the time to measure or test for dead zones. It's rarely done, if at all, in Australian clinics. In the NAL-NL2 prescription, we already devalue the importance of frequencies as hearing loss increases, and this goes at least part of the way towards giving up altogether when dead zones do occur.
Academy: Harvey, in the first chapter of the book you address what you refer to as "spatial processing disorders," and I thought it was brilliant and timely. Can you address that, please?
Dillon: Yes, well thank you. Spatial processing disorders (SPD) is a specific form of auditory processing disorders (APD). SPD might be described as the reduced ability to separate speech from noise using spatial cues, and it's most apparent in particularly noisy situations. This problem is one of the major reasons why people with sensorineural hearing loss fail to do well in noise, even with well-fitted hearing aids. That is, they are not able to benefit from the acoustic spatial cues that people with normal hearing use, in order to know where to focus their attention.
Academy: Right…that's one of my primary themes at this time. Knowing where to listen matters! Of course, some of the commercially available technologies help preserve interaural loudness and interaural timing cues, and I believe these are beneficial as they help the brain know where (in space) to focus attention. Harvey, what can you tell me with regard to "wireless" technologies? I suspect the majority of fittings across the globe don't involve wireless technologies, but to me, wireless is quickly emerging as the most significant game changer in the industry.
Dillon: I totally agree that wireless is a game changer. The applications that wireless technologies provide are going to eventually be looked at similarly to an entire "hearing-aid era." The advantages of wireless are staggering and are arguably larger than the advantages realized by going from analog to digital!
Academy: Can you give me a few examples?
Dillon: Yes, I'd be happy to. Let me say first that "wireless" is not one thing, it's many things. The big changes will come from transmitting audio signals from place to place, rather than just control signals from one hearing aid to the other. This becomes more feasible as the power consumption of transmitters and receivers reduce.
There's simply no substitute for placing the microphone right next to the person speaking to maximize the sound quality and the signal-to-noise ratio – and wireless systems allow this to occur. Wireless also facilitates something called "super-directional" hearing, which may provide the wearer of these hearing aids to do better than people with normal hearing in challenging and noisy acoustic environments. Super-directional technology comes from having two mics on each hearing aid and allowing the total of four microphones to communicate and decide where to focus their sensitivity using a relatively narrow directional beam, based on multiple parameters.
Academy: Harvey, I appreciate your time and I know you have to run! So then, we'll record and publish part two of this interview in the near future. In the meantime, we'll proceed with what we've got (earlier) as the information is important and timely, and I encourage hearing health-care professionals to get a copy of Hearing Aids and start reading!
Dillon: Thanks, Doug. I appreciate your interest in the book and I thoroughly enjoyed our discussion. Speak with you soon!
Harvey Dillon, PhD, is the director of research at the National Acoustic Laboratories in Sydney, Australia, and author of Hearing Aids (Second Edition), published in 2012 by Boomerang Press, distributed by Thieme Publishers.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content Editor for the American Academy of Audiology.
Cox RM, Alexander GC, Johnson J, Rivera I. (2011) Cochlear Dead Regions in Typical Hearing Aid Candidates: Prevalence and Implications for Use of High-Frequency Speech Cues. Ear & Hear 32(3):339-348.
Pittman A. (2011) Age-Related Benefits of Digital Noise Reduction for Short-Term Word Learning in Children with Hearing Loss. Journal of Speech, Language and Hearing Research 54 (October):1448-1463.