Probe-mic measures made easy

New clinician-friendly book by leading expert audiologist H. Gustav “Gus” Mueller, PhD, helps boost understanding of speech mapping in hearing aid fitting. Read what Dr. Mueller has to say about his new book, Speech Mapping and Probe Microphone Measures. 

A conversation with audiology expert Gus Mueller

Gus Muller

Peter Kossek, Senior Product Manager from Otometrics sat down with H. Gustav “Gus” Mueller, Ph.D. Audiologist to talk about his new book from Plural Publishing entitled 
Speech Mapping and Probe Microphone Measures.

Otometrics:  We are here with Dr. Mueller and the lead author of the recently published book from Plural Publishing titled Speech Mapping and Probe Microphone Measures. This is the first book written on this topic in 25 years—perhaps appropriately, the text published in 1992 also was senior-authored by Dr. Mueller. The book is clinician-friendly, engaging, and easy to read, with seven chapters and many useful figures; a total of around 300 pages.  

Gus, can you tell us a little about the book, and your inspiration for writing it?

Dr. Mueller:  First, I need to give credit to the assistance from my co-authors, Todd Ricketts and Ruth Bentler. Over the past four years, Todd, Ruth and I have written three other hearing aid books, also published by Plural Publishing, in which we have tried to cover the selection and fitting of hearing aids from A to Z. These three books are quite detailed, and more or less were written as college textbooks. When I’ve conducted workshops I frequently run into individuals who are just getting into doing probe-mic measures. They don’t really want a big book about everything, but rather a handbook that is focused on this verification procedure. So, we used a couple probe-mic chapters of our previous book as a foundation, and then built on that to create the Speech Mapping and Probe-Mic book.

Otometrics:  So you would consider it a handbook for the clinician/practitioner rather than a textbook?

Dr. Mueller:  Right.  We’ve made it very clinician-friendly, with many examples and clinical cases.  We also are aware that in the U.S. and many other places in the world, there is a large percentage of individuals dispensing hearing aids who are not audiologists. We’ve tried to add enough background information that this could be a useful book for them too. Actually, it would be a great textbook for a probe-microphone measures class, but typically we don’t see classes on this topic alone.

Otometrics:  The title of your book uses both the terms “speech mapping” and “probe microphone measures.” Do you consider these two different things?  

Dr. Mueller:  Funny you should ask, as we devote three pages in the book to that very topic. Some people also call it “real ear measures” or simply “REM”, so I guess that we could have included that term in the title too. The short answer is that most of the time, these procedures are the same thing.  Now, some aspects of probe-mic verification do not use a speech signal, so probe-mic isn’t always speech mapping.  But, you can’t do speech mapping without a probe-mic in the ear canal, so speech mapping is always probe-mic. To be honest, in these days of Google searches, we thought it best to use both terms in the title simply to help people find our book!

Otometrics:  Makes sense. Do you see the timing of this book as important?

Dr. Mueller:  As I mentioned, we did realize that there wasn’t a book on the topic; the other probe-mic book has been out of print for years.  And, clinicians seemed hungry for specific information—we were always bombarded with questions at our workshops at Vanderbilt.  I must say that the timing also is good relative to the discussion of the past couple years regarding PSAPs, OTC products, and the general delivery system of hearing aids today.  If you want to separate yourself from the pack, then a good starting point is to follow Best Practice Protocols, and I’ve yet to see a hearing aid fitting Best Practice Protocol that didn’t call for probe-mic verification.

Speech mapping
Gus Mueller at the Otometrics booth during AAA 2017 conference

Otometrics:  Are you suggesting that there currently are many audiologists and dispensers fitting hearing aids that are not doing probe-mic verification measures?

Dr. Mueller:  Unfortunately, yes. Of course there are many clinics and offices that do it religiously, but my best guess is that overall compliance may be no higher than 20-25%.

Otometrics:  Why is this?

Dr. Mueller:  I really don’t know.  We spend most of Chapter 1 talking about this, and clearly explain why it’s highly unlikely that it’s about money, time, not having the equipment, or training—the most common excuses.  It seems to be more of a mind-set.

Otometrics:  Could it simply be that there are better ways to verify hearing aid performance?

Dr. Mueller:  I can’t imagine what that would be. Audibility is a pretty fantastic thing.  If nothing else, probe-mic measures will tell us if we’ve made the speech signal appropriately audible.  But it’s really more than that.  When we do the initial programming of hearing aids, we have to start someplace, and there is no better place to start than with a validated prescriptive fitting—we have both the NAL-NL2 and the DSLv5.0.  Considerable research has shown that the only way we know that we have these fitting algorithms in the ear canal is to measure it.  Looking at a simulation on a fitting screen doesn’t work!  Additionally, considerable research has shown that greater patient benefit and satisfaction will be obtained when individuals are fitted with a validated method rather than some alternative approach.  Why take short-cuts when we are dealing with something so important to the patient’s lives?

Otometrics:  Do you also see the verification process as a positive for clinicians?

Dr. Mueller:  Absolutely. First, it’s just feels good to do the right thing. But moreover, as a result of verification, their patients will be performing better out in the real world, and consequently will be promoting the use of hearing aids to their friends. Research has also shown that the verification process enhances the image of the professional in the patient’s eyes, increases satisfaction with the fitting process, and improves patient loyalty.  

Otometrics:  And what about the hearing aid manufacturers?

Dr. Mueller:  Several studies have shown that patients’ speech understanding performance is enhanced when they are fitted with the real-ear verified NAL algorithm rather than the manufactures’ default strategy. This can be particularly critical for features such as directional processing, noise reduction and frequency lowering. We would assume that manufacturers want their products to be functioning optimally, so yes, real-ear verification is a big plus for the manufacturers too.

Otometrics:  We can’t agree more, and hope that your book will encourage increased use of this important component of hearing aid fitting.  Before we finish, can you tell us how you happened to work with Otometrics during the writing of the book?

Dr. Mueller:  Our presentation and teaching points throughout the book is through the use of a lot of illustrative cases. We show real-patient examples of just about every probe-mic measure you can think of, and also examples of possible mistakes that could be made. Peter Kossek and the folks at Otometrics kindly loaned us probe-microphone equipment so that we could conduct these measures, and also provided some background informational material.

Otometrics:  Thank you for joining us today, Dr. Mueller. I am sure your new book will help many clinicians understand the value of performing probe mic measures.

You can order Gus’ new book here:

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