Interview with Michael J. Metz Ph.D., Audiology Associates, Irvine, California, and Epic Hearing Healthcare

Topic: Signal-to-Noise Tests, Inner Hair Cells & AR

(www.epichearing.com)

AO/Beck: Hi Mike. Thanks for meeting with me today. Let's start with your education and professional history. Where did you get your doctorate and when?

Metz: I got my doctorate in 1972 from the University of Denver in Speech and Hearing Science.

AO/Beck: What was your dissertation on?

Metz: My dissertation was titled Nystagmographic Responses from the Posterior Semi-Circular Canal.

AO/Beck: That's a little out of the ordinary! What did you learn?

Metz: I learned that you ought to do research on normal subjects because there are a lot more normal subjects around than there are abnormal!

AO/Beck: I can only imagine how many of the readers are nodding their heads and saying if only I knew that then. So you developed norms for electronystagmography and related nystagmographic phenomena?

Metz: That's what we tried to do. It didn't pan out very well and was doomed to oblivion, but it was kind of fun at the time.

AO/Beck: I believe you were also the founder of Audiology Associates, a private audiology practice?

Metz: Yes, it's a private practice. It grew nicely through the 70's and 80's and began to wind down during the 90's. In the new millennium we have one employee, me. The chairman of the board, my wife, elects me as employee of the month every once in a while when I do things right.

AO/Beck: Perhaps you could talk a little about Epic?

Metz: Yes. Epic is an alliance of audiologists and otologists. We have some 650 members now. Approximately 450 of them are audiologists, maybe 50 are general ENT people, and probably 200 or so are otologists across the country. It's a network primarily based on the question....Who would you send a patient to if you had patients you weren't going to treat? You'd most likely send them to somebody you knew, and somebody whose reputation was excellent, would uphold your reputation, and would provide quality care. That's the idea behind Epic.

AO/Beck: Who founded Epic, and how long has it been around?

Metz: Epic was actually started by a number of people. There were a couple of physicians from the House Ear Clinic, and a couple from Stanford Ear and others from around the country. The original company was called Earmark and it failed in the first go-round, primarily because audiologists weren't involved. I came in about five years ago to see if we could create a company that was concerned with all aspects of hearing care. We incorporated audiologists as an integral part of the diagnostic and therapeutic process and the company is doing very well.

AO/Beck: Mike let's talk a little bit about your presentation at ARA* in July of 2003, regarding signal to noise testing.

Metz: Sure thing. The presentation focused on the necessity and benefits of using signal-to-noise testing to determine a starting point in auditory rehabilitation. This approach is based on the theory that it's hard to perform therapy if you don't know where you're starting, and if you don't know what the therapeutic goals are! Measuring the starting point and the goals provides obvious advantages.

AO/Beck: When you talk about signal-to-noise tests as a starting point, which tests do you prefer?

Metz: Well, there are really only two tests that are clinically applicable for this kind of measurement. One is the QuickSIN, and the other is the HINT for Windows. I'd like to add that the HINT for Windows is a different test than the HINT test. The HINT test was originally used to evaluate cochlear implant strategies. HINT for Windows is more precise. Both the QuickSIN and the HINT for Windows are good tests. The normative data sets are well defined and equivalent and they produce pretty much the same results, although I am partial to HINT for Windows.

AO/Beck: Who produces that and where is it available?

Metz: HINT for Windows is available through Maico Diagnostics.

AO/Beck: If I were to give the HINT for Windows test, what would the patient experience?

Metz: In both the HINT for Windows and the QuickSIN tests, the patient listens to simple sentences or simple words in the presence of background noises. The Quick SIN uses a babble noise masker; the HINT uses a balanced speech spectrum masker-not exactly pink noise, but balanced to the spectrum of the speech signals used. Since the HINT uses a more predictable and precise masker, this test has slightly better specificity and sensitivity. The standard deviations are smaller and the repeatability is higher. However, the newest version of the QuickSIN has normal data approximately equal to the HINT.

AO/Beck: How might a typical, normal hearing adult score on these tests?

Metz: In both the QuickSIN and the HINT, when speech and noise are presented from a single point position, such as from one speaker, they produce about the same scores, essentially a -2.5 dB signal-to-noise ratio threshold, which constitutes the 50% identification point on a response distribution. The HINT goes one step further; it can measure what happens when the signal and noise are not at the same spatial point. For example, with speech in the front of the listener, and with noise at the side (either 90o or 270o), a normal listener will show a SNR threshold value of about -9 or -10 dB.

AO/Beck: And that makes it an easier task for the listener?

Metz: Well not necessarily an easier task, but certainly a different task. In patients with bilaterally symmetrical hearing, we notice a squelch effect that the listener gets when they position a speaker advantageously relative to competing noise.

AO/Beck: Okay. So if we say that -2.5 dB would be about the 50% point, indicating that if the noise is 2.5 dB louder than the speech signal, most normal hearing people, and even many people with bilaterally symmetric hearing losses will identify some 50 percent of the speech correctly. How do we use this to diagnose hearing aid candidacy and how can we use it therapeutically in AR?

Metz: Certainly you can measure it and use it diagnostically. Killion has suggested there are people with specific signal-to-noise losses. He has also suggested that the relationship between signal-to-noise ability and functional hearing in the presence of noise is not highly related to pure tone configuration or degree of hearing loss, and that's also true. The interesting thing to me is that many clinicians seem to assume this hearing in noise difficulty can be predicted from the audiogram, but the data suggests that is not the case.

AO/Beck: So in other words, if we take two identical, typical presbycusic presentations, in two 68 year old patients, with a 30 dB loss at 500 and 80 dB at 8k, one can score quite well and the other can do absolutely miserably, right?

Metz: That's correct. And the assumption is that this may be the reason why some people with a given hearing loss do very nicely with hearing aids, and others, with the same type and degree of hearing loss, fail miserably. My paper at the ARA meeting asked; if you could divide these patients into groups, would you approach them differently, and change your rehabilitative strategy? I answered that if we knew who the better performers were, and who the worse performers were, we certainly would treat them differently, and conclusion was, you probably ought to do these kinds of measurements to know which patient is which!

AO/Beck: Excellent point! I wonder if, when we separate these people by their speech in noise ability, we're diagnosing inner hair cell deficits?

Metz: That's exactly the point I tried to make at the ARA meeting. Intuitively one would assume that, if pure tone hearing loss is highly correlated with outer hair cell viability, and hearing in noise is not correlated with outer hair cell viability, then there would be only one other functional mechanism contributing to SNR ability, and that's the inner hair cells. In fact, if one collapses data and research from the past into categories, you come to the conclusion that there is likely a very close relationship between dead regions, tuning curves, global tuning function for speech, and the inability to hear in noise. The inner hair cells likely function as gatekeepers and the depth of the tuning curve and/or precision of the inner hair cells are probably what's being measured in signal-to-noise testing.

AO/Beck: Now just to muddy the waters completely... How would you isolate a signal-to-noise patient from a true central auditory processing disorder patient? I am guessing here, but it seems the two would both do poorly on the signal-to-noise tests?

Metz: Well, they may and they may not. There're some interesting suggestions that children with ADHD correlate highly with central auditory problems on these measures, and they often do not score well on the HINT test. However, there's another interesting thing to look at; if in fact the central nervous system is so plastic that it can manage fairly significant changes, particularly in children, one wonders why it wouldn't manage the changes that occur from altering the peripheral mechanism. That is, if the peripheral mechanism fails to provide correct input, does the central mechanism alter? How much can it change and how contributory is this change or lack of change to a central auditory problem?

AO/Beck: Excellent points. So in fact, the APD patient could have APD secondary to inner hair cell anomalies?

Metz: That's exactly the point. I'm not so sure that when we measure central auditory problems we have necessarily eliminated peripheral contributions with the typical auditory tests.

AO/Beck: And if possible, anatomic specificity would be very nice.

Metz: It would be wonderful. EPIC has an insurance plan about to come to the market, which uses these kinds of measurements in order to predict what type of hearing aid might stand the best chance of providing an outcome appropriate for more aspects of the hearing loss. We are promoting these tests and we hope more clinicians will start using them.

AO/Beck: What percentage of professionals are actually looking at speech-in-noise?

Metz: I can't answer that. It's taken us almost 10 years to get a few audiologists to look at intelligibility in the presence of noise. If I had to guess, I can't imagine the number being more than 10 %. I broke this down a while ago and collapsed the available data to determine that if you were a patient who got off of a bus in any city in the United States, and walked into the first hearing aid office you came to, the likelihood of you being fit with hearing aids according to complete audiologic science is less than 10%, and maybe as low as 5%. In other words, people fit hearing aids based more on art than science. And unfortunately, the art is variable, while the science is extremely good, but not used often! However, technology is not the whole answer, rehabilitation is the greater part of the answer and the way you apply rehabilitative therapy is to measure the problem, predict the probable outcomes, approach the problem in a reasonable way based on measurements and science, and work towards a given, predictable conclusion.

AO/Beck: And as we know, the primary complaint from hearing aid wearers is their ability to hear speech-in-noise. Although we can, we don't typically measure that, so we cannot really determine benefit, changes and outcomes with regard to speech-in-noise.

Metz: Correct.

AO/Beck: Thanks Mike. These are great issues, and I appreciate your time in addressing them here today.

Metz: Thank you too, Doug. It was fun.

*ARA: The Academy of Rehabilitative Audiology was founded in 1966 to promote excellence in hearing care through the provision of comprehensive rehabilitative and habilitative services. Each year the ARA hosts the ARA Summer Institute which provides a forum for discussion on the latest developments in auditory rehabilitation research and therapy. ARA membership is open to anyone conducting research or providing services in the area of audiologic rehabilitation. For more information visit www.audrehab.org or call the national office at 952-920-0484.