Interview with Don Schum Ph.D., Vice-President for Audiology and Professional Relations. Oticon, USA

Topic - Non-linear amplification for severe and profound hearing loss

AO/Beck: Hi Don. I know many of the readers are familiar with you. Nonetheless, if you would just give me a brief overview of your education and professional history, that would be great.

Schum: Sure Doug. I earned my doctorate in 1988 from Louisiana State University in Baton Rouge, and it's in Audiology.

AO/Beck: What was your dissertation on?

Schum: My dissertation was on speech perception issues. Specifically, I examined the time course of phoneme perception comparing normals to patients with sensorineural hearing loss to see how much of a phoneme they needed to correctly identify the phoneme.

AO/Beck: Did that exploration lend itself towards time-compressed and time altered speech?

Schum: It could. I used naturally produced speech but the assumption was that if hearing impaired individuals had to spend more time on a phoneme-to-phoneme basis before they got the overall perception, their task would be a more laborious process, and that could open the door to time compression and related issues.

AO/Beck: Don, how long have you been with Oticon and what is your position please?

Schum: I'm Vice-President for Audiology and Professional Relations in the US office of Oticon. I've been with Oticon for eight years, three of those were at the main office in Copenhagen, and the last five years being here in the US.

AO/Beck: I'd like to focus on the topic you presented at the ARA* meeting in Kerrville, Texas, in June of 2003? I believe you spoke about non-linear hearing aid technology for patients with severe and profound hearing loss?

Schum: Yes. There's been discussion in the literature and in professional training over the last couple of decades about whether or not non-linear amplification is appropriate for patients with severe or profound hearing loss. Some early studies from the 1970's and 1980's cast doubt on whether or not patients with that degree of hearing loss could get enough information after it was processed through compression amplification.

At Oticon, we've been interested in examining this issue. We verified that patients with severe and profound hearing loss can perform well with compression amplification, compared to linear amplification, as long as certain considerations are made in the set-up of those systems.

AO/Beck: Can you talk a little bit about those considerations please?

Schum: Sure, but let's start with the basic advantage of using dynamic range compression, which is to make more everyday sounds, especially soft or moderate speech, audible to the patient. That advantage should make sense for patients with severe-to-profound hearing loss because they have a significant audibility loss and they have a limited dynamic range. Theoretically, they should be able to benefit from a broader dynamic range of signals being compressed into a smaller output dynamic range in their ear. The fundamental issue is the way compression takes place. Most attempts have very fast acting compression, in which some of the intensity relationships on a phoneme-to-phoneme basis get minimized or eliminated. We tend to favor slow acting compression systems. We've seen good results in patients with severe and profound hearing loss using slow acting compression systems.

AO/Beck: With regard to slow versus fast acting compression systems, would you please define those for me?

Schum: Fast acting is defined by the release time of the compression system. Typically, release times less than 100 milliseconds are defined as fast acting syllabic compression systems. Those are probably the most common systems on the market. Oticon has made a strong case, and has developed a series of products using slow acting, longer release times, from half a second to 2 or 3 seconds. The basic advantage of the slower acting release times is that the phoneme-to-phoneme intensity relationships are not disrupted. We believe there's a significant amount of information in those relationships, especially for patients with severe to profound hearing loss, and maintaining the integrity of the signal is very important. In other words, with slow acting release times, they're going to receive a signal where the amplitude cues in the signal are more like unaltered speech.

AO/Beck: I see. It makes good intuitive sense. Preserving the natural intensity relationships seems like it would be a good idea! But then, what kind of compression ratio are you talking about for dealing with severe-to-profound loss, because these folks do have very limited dynamic range?

Schum: Yes, good question. The dynamic range is limited, and so you'd be talking about compression ratios of about 3 to 1, or perhaps 4 to 1. We tend not to push it beyond that because even in the slow acting system, going beyond 3 or 4 to 1 is probably too much. We'll take a little bit more conservative approach and try to maintain no more than a 3 to 1 ratio most of the time.

AO/Beck: Which of your non-linear power products are designed with slow acting release and a 3 to 1 compression ratio?

Schum: We have three tiers of products that fit the bill for severe hearing loss. Atlas is a two-channel non-linear unit, and we'll be releasing a power version soon. The next tier up is what used to be called DigiFocus. We're in the process of replacing DigiFocus with Gaia. At this point, Gaia is not available in a power unit, but DigiFocus is. The top of our product line is Adapto, and that is available in a power unit. The three units I just mentioned use a 13 battery. The most powerful units we have for profound hearing losses are the DigiFocus Super Power, which uses a 675 battery, and our other product for the profound range is SUMO, and that is a linear product.

AO/Beck: Can you compare results obtained with the linear SUMO model, to results obtained using compression aids, for the same groups?

Schum: Yes, we've been studying patients in the profound category on our most powerful products, such as SUMO compared to DigiFocus Super Power. Basically, the results are a mixed. Some patients do better with the linear product and some patients perform better with the Super Power. We have data for patients in the severe category, in the severe-to-profound category, and in the profound category. In the severe and severe-to-profound categories, there is objective data and importantly, subjective data, which indicates they are performing better on speech understanding tests with non-linear hearing aids.

AO/Beck: How did you measure the subjective data?

Schum: We have a series of questionnaires that we've developed locally and then used across the different studies. Subjectively they report doing well in a broader range of environments, and that is consistent with using non-linear hearing aids.

AO/Beck: Why do professionals seem to grasp onto linear aids for people with severe and profound hearing loss?

Schum: I think professionals grasp onto linear hearing aids because there was an assumption made, many decades ago, that patients in these categories had a hard time adapting to non-linearity. I think that experience shaped a lot of audiologists thinking at the time and there was not much attention to the issue after that, so the status quo was maintained.

AO/Beck: Can you discuss the role of a volume control in compression versus linear fittings?

Schum: When we produce any power or super power product even if it's non-linear we include a volume control, and we refer to it as a manual override. The reason we do that is to try to limit the amount of compression we use. We would rather limit the amount of compression or limit the compression ratio knowing that we are probably not providing the full range of input into the patient's ears, while allowing them to make adjustments with the manual override, or the volume control.

AO/Beck: When they use the manual override, they're not impacting the compression ratio, is that correct?

Schum: Yes, you're correct. No, they're not impacting the compression ratio and indeed, the product is still programmed as if it's a fully automatic unit with the target being good to excellent performance for moderate input levels. But if they're in an excessively soft environment or an excessively loud environment, the manual override can be used to make situational adjustments. It's a compromise between the idea of having a full compression system and a fully automatic fitting with the need for maintaining a minimal compression ratio and giving situation specific control to the user.

AO/Beck: OK, that makes sense for non-linear units with VCs. One more question then, in this scenario with compression fittings for severe-to-profound hearing loss, is there any impact on the spectral response?

Schum: There should not be. It should be a straightforward change in just the loudness level presented to the ear.

AO/Beck: In the linear SUMO, when you manipulate the VC, you will get a difference in the spectral response, won't you?

Schum: Yes, very possibly. For the most part it's going to maintain the spectral shape pretty well, although it could change depending on the specific circumstances.

AO/Beck: This really is interesting because it's almost re-introducing higher levels of technology into an area where many professionals have already made up their minds, and perhaps you're forcing them to look at it again and say, Well now that we have better technology, we need to reexamine this question.

Schum: Right. That's exactly what this is all about. We believe advanced non-linear technology for severe to profound hearing loss has been underused. I think most professionals agree that if possible, multi-channel, non-linear circuits is the way to treat sensorineural hearing loss when possible, and I think we're seeing the introduction of expanded applications, and better tools. When we started to develop our non-linear power products, we developed them based on the philosophy that they had to be power products first. We believe some of the commercial failures to reach sever and profound hearing losses with non-linear circuits simply did not have the gain or output required. But the failures may not have been based on non-linearity, and may well have been due to a lack of gain and MPO.

AO/Beck: Don, before I let you run, I know you have a great AR program for kids. Can you tell me a little about that?

Schum: Absolutely. Otto's World of Sound is the program. Otto is the Oticon mascot so to speak. We developed an at-home auditory training program for children, based on environmental sounds. It was developed by a couple of gentleman from France. They had a wonderful program they were using in French, and we contracted them to do a reduced version called Otto's World of Sound for use across the world. It's available on CD-ROM for at-home use by children, parents and other family members. We decided to create an at-home version because the service model varies so much across the USA and the world, that we thought it was important to make the tools available. If it's used with professional guidance that's another plus, but even using it with mom and dad is very useful. Giving the family members an opportunity to be part of the process is really a plus.

AO/Beck: Don, I know we're in time trouble here. Thanks so much for sharing your thoughts on non-linearity. I'm really excited to see how this approach pans out for severe and profound hearing losses.

Schum: Thank you too, Doug. I appreciate the chance to get this information to the AO readers.

*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.

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