From the desk of Gus Mueller
Clinical audiology can be a funny business sometimes. Not too long ago I saw an article relating to research that examined the most appropriate presentation level for conducting word recognition testing. After 70 years, wouldn't you think we would know? There was another recent article questioning if probe-mic measures were really necessary when fitting hearing aids. After 30 years, wouldn't you think we would know? And then, just when it seems like the wheels of audiology are barely turning, thankfully, along come some articles on cochlear implants.
Many of you are old enough to remember the days when it was considered pretty amazing that a cochlear implant patient could communicate using the telephone. That wasn't all that long ago, and a lot has changed since then. One area that has received considerable attention in the past ten years is cochlear implantation with hearing preservation using what is referred to as electric and acoustic stimulation (EAS) or a hybrid implant. We just happened to locate an expert on this topic, who is our guest this month for 20Q.
René Gifford, Ph.D. is an assistant professor at Vanderbilt University and the Director of the Cochlear Implant Program and Pediatric Audiology at the Vanderbilt Bill Wilkerson Center. She also directs the Cochlear Implant Research Laboratory at Vanderbilt and is actively involved in graduate student training. You're probably familiar with the many articles and book chapters related to cochlear implants authored by Dr. Gifford.
René only recently came back "home" to Vanderbilt, the site of her early audiology training. In her "free time" when not working on her forthcoming book on cochlear implant assessment for Plural Publishing, you can probably find her at a baseball or football field, chasing down one of her three sons. We were lucky to chase her down; I'm sure you'll enjoy her contribution here at 20Q.
To browse the complete collection of 20Q with Gus Mueller articles, please visit www.audiologyonline.com/20Q
Editor's note 10/7/11: There have been rapid changes in the field of cochlear implantation thanks to ongoing advances in research and technology. Just since this article has been published, there are some very recent developments in EAS research at the University of Iowa. In the last three months, they have been given FDA approval to conduct two feasibility trials to study preservation of hearing with Nucleus hybrid cochlear implants in those with severe hearing loss and will be implanting children between the ages of 5 and 15 years of age. This new information about the Iowa-sponsored feasibility trials contradicts two points within questions 15 to 18 of the article: Adults with greater hearing impairment than those in the clinical trial described in the article are eligible for implantation with a Nucleus Hybrid L24 implant through the Iowa-sponsored feasibility trial, and the S12 and L24 devices are available to children through the feasibility study at the University of Iowa. Please keep this is mind as you read the article. As new advances are made in this exciting area of research and practice, we will try our best to keep you informed!
1. Before we get started, I need to clear up one thing. I thought the patient sacrificed all remaining hearing when they had a cochlear implant?
For years that was the case. The earliest criteria for cochlear implant candidacy required bilateral profound sensorineural hearing loss and in fact, many patients had absolutely no residual hearing. Thus, hearing preservation was not even something that was considered an option. As cochlear implant criteria have evolved, more and more individuals with residual low-frequency hearing are qualifying for cochlear implants. Further, you are right in that it was always assumed that the surgical insertion of the electrode array would cause irreparable damage to the delicate intracochlear structures.
And, you're not too far behind in your thinking. Hearing preservation with cochlear implantation is still considered a relatively new topic. The first published paper describing hearing preservation in a human was published by Christoph von Ilberg and colleagues in 1999. Today, we usually refer to these as electric and acoustic stimulation (EAS) or hybrid cochlear implant patients (e.g., implant + hearing aid in the same ear).
2. So is this something that is routinely being done?
Well, yes and no. To some extent it relates to the accepted criteria. Current audiometric cochlear implant criteria for adults range from moderate to profound sensorineural hearing loss for Medicare and Cochlear Corporation and severe to profound sensorineural hearing loss for Advanced Bionics and Med El. Current pediatric implant criteria specify profound sensorineural hearing loss for those under 24 months and severe to profound loss for those over 24 months. So, many of the patients being referred for cochlear implant evaluations have very little residual hearing to start. But, another confounding factor is that most cochlear implant programs do not routinely assess postoperative "unaided" hearing status in the implanted ear. Thus it is suspected that many more patients have preservation of some acoustic hearing but are not necessarily aware.
3. Makes sense, but why do different manufacturers have different implant criteria?
The labeled indications result from independently sponsored FDA clinical trials. That is, each manufacturer goes to the FDA separately and as a result, have slightly different candidacy criteria.
4. Are surgeons guaranteeing patients that they will maintain acoustic hearing following this type of cochlear implant surgery?
The short answer is...absolutely not! Patients are much more savvy these days with the availability of information online—albeit not always good and accurate information. Many patients will come into their cochlear implant evaluation appointments with references about hearing preservation and occasionally, the audiology and surgical teams will be asked about a "guarantee" for hearing preservation. I am not aware of any cochlear implant center that would be willing to provide such a guarantee, though there are certainly factors that have been shown to be more likely to result in preservation of low-frequency acoustic hearing. For example, individuals with lower, i.e. better, audiometric thresholds are more likely to have preservation of acoustic hearing. The reason is that research has shown that most patients who have hearing to preserve will on average lose anywhere from 10 to 25 dB following surgery (e.g., Gantz et al., 2009; Gstoettner et al., 2008). In other words, the more you have to preserve, the better.
Another group of factors known to affect hearing preservation are the physical characteristics of the electrode array. Some arrays are characterized as more "atraumatic" than others. Those would include a small diameter (</= 0.5 mm), flexible tip, and also a shorter overall electrode array corresponding with a shallower insertion depth. There are also surgical factors like cochleostomy location or even round window insertion that have been shown to affect hearing preservation (the cochleostomy is the hole that the surgeon drills into the bony labyrinth through which the electrode array is inserted). Another factor that is gaining increased attention is the administration of steroids. Steroids are used therapeutically for a myriad of conditions ranging from asthma to arthritis. One of the main applications of steroid treatment is in the reduction of inflammation. Thus steroids are being administered both locally and systemically in an attempt to counteract the inflammatory response following surgical insertion trauma. Of course, there is considerable debate over the appropriate dosage as well as the means and time course of administration. There are also a number of surgical techniques shown to affect hearing preservation…but I’ll try to keep this discussion more audiology-relevant.
5. You mentioned a shorter electrode array. Does that mean that there are special implants made specifically for hearing preservation?
Yes there are. In the U.S. there are currently two active FDA clinical trials surrounding hearing preservation with cochlear implantation for individuals with relatively good low-frequency hearing (defined as thresholds </= 60 dB HL through 500 Hz) and severe-to-profound hearing loss in the high frequencies. The implants included in these trials are 1) the Nucleus Hybrid devices (S12 and L24) from Cochlear Corporation, and 2) the Flex EAS device from Med El.
6. You said two trials, but you mention three devices. Can you elaborate?
You are correct, there are more than two devices. Let me back up a bit. The Cochlear Corporation began their clinical trials with these shorter, narrower, more atraumatic electrodes many years ago first with an electrode array that was inserted just 6 mm beyond the cochleostomy. It was implanted in just three patients and due to poor speech recognition outcomes and ultra-high pitch percepts, it was abandoned for a longer array, with a deeper insertion and more electrodes (Gantz & Turner, 2003). Thus the Hybrid S8 was introduced. The S8 was inserted to a depth of 10 mm beyond the cochleostomy and there were 6 intracochlear electrodes plus the 2 extra-cochlear ground electrodes which is where the 8, in S8, originated. Around the same time, Med El was trialing with their EAS implant in Europe across multiple clinical trial sites. The Flex EAS device is inserted to 20 mm and has 12 electrodes. The Flex EAS device is the same device currently under clinical trial in the U.S.
7. How many patients have been implanted with these devices?
Eighty-seven patients were implanted with the S8 device in the U.S. and the outcomes were generally quite impressive. Patients were only losing, on average, 10 to 20 dB following surgery in the low frequencies (e.g., Gantz et al., 2009) and 91% of the patients had some degree of hearing preservation over time. Preserved acoustic hearing in the implanted ear was amplified with an in-the-ear (ITE) hearing aid that was worn along with the patient's cochlear implant sound processor. Clinical trials of the Med El EAS system in Europe were conducted at multiple sites and the published studies have reported on subsets of patients ranging from 18 to 95 EAS implant recipients (e.g., Helbig et al., 2011; Skarzynski et al., 2010). The Med El EAS sound processor, called the DUET, had an integrated hearing aid requiring only a single device with earmold for the implanted ear.
8. How does hearing preservation compare across these different devices?
On average, studies published for the Hybrid S8 and Med El EAS recipients have yielded similar findings. The degree of post-implant hearing loss with the Med El EAS tends to be more than that observed with the Nucleus Hybrid S8, which was not an unexpected finding given the much deeper electrode insertion (Kiefer et al., 2005; Gstoettner et al., 2008). Speech recognition outcomes were found to be quite similar across the Nucleus S8 and Med El EAS patients except for one major difference: for those patients that unfortunately lost all acoustic hearing following implantation. For the patients with near or complete loss of hearing, it was found that the shallow 10-mm insertion of the Hybrid S8 was generally not able to provide them with high levels of speech recognition on its own. Thus these patients have often been requiring an explant of the S8 and a re-implant with a conventional long electrode array (e.g., Fitzgerald et al., 2008; Carlson, Gifford, Archibald & Driscoll, in press B). So, Cochlear Corporation came up with two new electrode options: S12 and L24.
9. So, there are even more electrode options than those already described?
Yes, but keep in mind that the Hybrid S8 and the earliest 6-mm electrode are no longer in clinical trial. So, the currently available Hybrid electrodes are the S12 and the L24. The Hybrid S12 is still inserted just 10 mm beyond the cochleostomy, but it has an additional 2 intracochlear electrodes for a total of 10 electrodes plus the two extracochlear ground electrodes (alas S12). This device is being used to investigate whether the addition of more electrodes with a shallow insertion will be sufficient to provide enough electrical stimulation should the patient have significant or total loss of acoustic low-frequency hearing. At the same time, Cochlear is also trialing the Hybrid L24 for which L stands for "long" and 24 for 24 electrodes (22 of which are in the cochlea). The Hybrid-L24 is inserted 16 mm beyond the cochleostomy. Thus, the L24 has appealed to those cochlear implant centers believing that a deeper insertion depth is required for higher levels of electric-only speech recognition and that the increased risk for low-frequency hearing loss associated with a longer array is offset by the benefits afforded by more electrodes spaced along a greater cochlear length. Since these multi-center trials are currently ongoing in the U.S. and enrolling participants, there are not much data to describe at this point. However, based upon presentations that I've attended and some papers coming out of Europe and Australia, the preliminary findings are that 1) both the S12 and the L24 have yielded better speech perception outcomes than the Hybrid S8 device, 2) there is greater post-implant hearing loss associated with the deeper insertion depths (i.e., L24 and Flex EAS result in more low-frequency loss than S12), 3) recipients of the longer electrode arrays (Hybrid L24 and Med El Flex EAS) exhibit electric-only speech recognition scores comparable to those with conventional, long electrode implants, and 4) outcomes for recipients of the Hybrid L24 and Med El Flex EAS electrode array are essentially equivalent.
10. That's a lot of information. Can you make it easy and just tell us what's the best device?
Unfortunately there is no simple answer. It is likely that when all the clinical trials end, there will be multiple available electrode options that will ultimately gain FDA approval. In terms of device selection, the choice may depend upon the risk/benefit ratio with which the individual patient and his or her surgeon feel most comfortable. If you are an individual who is most concerned about preservation and is fearful about losing even a little hearing, you would likely be best served with a shorter array, like the Hybrid S12. If you are someone who wants to maintain your hearing but also interested in maximizing the likelihood that should considerable hearing be lost that you'll continue to do well with your implant, then a longer electrode array is probably best for your needs, like the Hybrid L24 or the Flex EAS. It might even be the case that an entirely new atraumatic electrode option will surface in the near future. Oh and just one more thing...there are an increasing number of reports on hearing preservation following conventional, long electrode implantation. Maybe we'll get to that later.
11. So let's get practical. How well are these patients doing with their implants?
These patients are doing well postoperatively. The short story is that at the group level, patients are demonstrating significantly better speech recognition. The clinical trials are evaluating pre- and post-implant speech perception performance on measures of word recognition in quiet and sentence recognition in quiet and in noise. On all metrics, patients are demonstrating significantly higher postoperative scores at the group level. Gantz et al. (2009) reported that significant improvements in word and/or sentence recognition in noise scores were observed in 74% of the population. For those that did not demonstrate benefit, or who may have shown a decrement in performance, the duration of deafness for high-frequency stimuli was significantly and negatively correlated with postoperative performance. Thus, this finding led to Cochlear Corporation instituting a limitation on the duration of deafness for the S12 and L24 clinical trials of 30 years. For the Med El EAS recipients, Helbig et al. (2011) reported that monosyllabic word recognition increased from 20.6% to 64.8% after 12 months of experience with EAS. For sentence recognition, performance improved from 42.0% to 81.4% in quiet, and from 16.3% to 54.4% in noise (Helbig et al., 2011).
12. Other than the lab data, do we know how these patients are doing in the real world?
Yes we do, and the results are encouraging. They are reporting improved communication abilities in multiple environments. Helbig et al. (2011) reported a significant improvement on all four subscales of the Abbreviated Profile of Hearing Aid Benefit (APHAB) with EAS as compared to the preoperative scores with binaural hearing aids. Further, it has been reported that the recipients of the longer electrode arrays (Hybrid L24 and Flex EAS) are demonstrating electric-only performance that is comparable to that reported for conventional long-electrode cochlear implant recipients (e.g., Lenarz et al., 2009). Again, this is an important finding because should these patients lose hearing shortly following surgery or more slowly over time, their outcomes would be expected to be equivalent had they been implanted with a conventional cochlear implant. In other words, they wouldn't require a second surgery should they lose their hearing.
13. You've mentioned speech perception outcomes, but what about other types of perception, like music?
It's only been recently that we've had the luxury to assess music perception and appreciation in cochlear implant recipients. There was a time when this was not even considered. This is a testament to the benefit provided by this technology! But, this is not an easy question to answer because it is yet unclear how the acoustic and electric hearing combine not only across ears, but also within the same ear to aid music perception. There are, however, a number of studies reporting that cochlear implant recipients who have residual acoustic hearing outperform those who only hear via electric stimulation on measures of pitch perception and melody identification (Gantz et al., 2005; Gfeller et al., 2006; Gfeller et al., 2007). Kate Gfeller and colleagues from the University of Iowa have been examining various aspects of music perception in recipients of the Nucleus Hybrid cochlear implant (S8, S12 and L24) and have shown that these individuals outperform all other cochlear implant recipients—even those who have acoustic hearing in the non-implanted ear. What is not clear from those studies, however, is whether the improved performance is due to the preserved hearing in the implanted ear or to the fact that Hybrid/EAS patients tend to have better low-frequency hearing in even the non-implanted ear as compared to the other patients studied.
14. Did I hear you say earlier that hearing preservation also can be achieved with conventional long electrode implants?
Yes, I did say that. A number of studies have reported hearing preservation for conventional long-electrode implant recipients (e.g., James et al., 2005; Balkany et al., 2006; Fraysse et al., 2006). One of the most recently published and largest datasets, Carlson et al. (in press A) completed a retrospective review of 126 implanted patients who had met audiometric criteria for Hybrid/EAS preoperatively but who had received a conventional, long-electrode implant. It was found that 55% of the study population had measurable hearing postoperatively in the implanted ear. Further, there were a few patients who had actually been fitted with an ITE in the implanted ear to take advantage of the preserved hearing.
15. This all sounds promising, so if one of my patients were interested in pursuing this technology, what exactly are the criteria for inclusion in one of these Hybrid/EAS clinical trials?
First of all, this is only currently available to adults in the U.S. who are enrolled in an FDA approved clinical trial. Further, recipients of this technology must be enrolled in an FDA approved clinical trial. Audiometric criteria are slightly different across Cochlear and Med El but are generally thresholds up to 60 dB HL through 500 Hz and 70 dB HL or poorer at 1000 Hz and above. Hearing loss must be sensorineural in nature with no presence of cochlear malformations. CNC monosyllabic word recognition performance with appropriately fitted hearing aids must be no greater than 50% in the ear to be implanted for EAS and no greater than 60% for Hybrid. Finally, there has to be evidence of stable hearing because obviously, if the hearing loss is known to be progressive, perhaps a shorter electrode array with the aim of hearing preservation is not the best treatment option.
16. How does all this differ from conventional cochlear implant criteria?
Hybrid/EAS criteria are much more liberal than current FDA labeled criteria for cochlear implants. As I mentioned earlier, current adult cochlear implant criteria differ slightly across the three FDA approved manufacturers as well as across insurance types (Medicare vs. non Medicare) but generally include: moderate sloping to profound bilateral sensorineural hearing loss and no greater than 60% correct for recorded, open set sentence recognition performance in the best aided condition with appropriately fitted hearing aids. For Medicare, candidates can score no greater than 40% correct for recorded, open set sentences in the best aided condition.
17. You mentioned that only adults qualify for Hybrid/EAS in the U.S. Is this technology under consideration for children?
Most definitely; it already is being done in Europe. Skarzynski and Lorens (2010) describe outcomes for 25 children (mean age 9.5 years) with precipitously sloping hearing losses who were implanted with the Med El EAS implant system. Though all 25 children had hearing preservation in the implanted ear, only 22 of those children had aidable low-frequency acoustic hearing using the EAS DUET system (Skarzynski and Lorens, 2010). Speech recognition was significantly higher postoperatively for monosyllabic word recognition in both quiet and noise—this was true even for those children with considerable loss of low-frequency hearing. The degree of improvement ranged from 33 to 39% in quiet and 40 to 57% in background noise.
18. Isn't there concern that these children will lose low-frequency hearing over time?
Those concerns are certainly valid. However, Yao and colleagues (2006) examined audiometric thresholds longitudinally for 214 ears for which audiometric thresholds were within Hybrid/EAS candidacy and found that adults with hearing loss lose about 1.1 dB/year and children approximately 1.2 dB/year. Thus, the average rate of loss is not as rapid as one might think. Further, the benefits afforded by electric stimulation with the longer electrode array (such as the 20-mm Flex EAS or 16-mm Hybrid-L24) are comparable to that of a conventional, full-length array. So, if a child has a precipitously sloping high-frequency sensorineural hearing loss and is not demonstrating benefit from amplification, EAS could really provide them with high levels of speech recognition regardless of whether or not the hearing progresses over time.
19. So, I'm guessing that you've conducted some research in this area too?
I first started working with this population of patients while completing my postdoctoral fellowship in Michael Dorman's cochlear implant laboratory at Arizona State University. My postdoc work examined the psychoacoustic properties of low-frequency hearing both pre- and post-implant. A brief summary of what we found was that temporal processing was largely present preoperatively and preserved following implantation with either the Nucleus Hybrid S8 or the Med El EAS device. We also found that in most patients, frequency selectivity at 500 Hz was largely absent postoperatively and generally abnormal even preoperatively (Gifford, Dorman, Spahr & Bacon 2007; Gifford, Dorman & Brown, 2010). The most interesting finding was for those individuals with residual nonlinear cochlear processing at 250 and 500 Hz preoperatively—even if they had complete preservation of acoustic hearing—nonlinear cochlear processing was significantly poorer following surgery (Gifford et al., 2008). Thus we demonstrated that this test was more sensitive to the effects of surgical trauma than audiometric threshold, which was very exciting. This tells us that should the manufacturers introduce a more "atraumatic" electrode or if surgeons devise new minimally traumatic surgical techniques, that we have a metric to assess the validity of these claims. On the flip side, however, we found absolutely no correlation between residual cochlear nonlinearity and speech recognition outcomes. This was also reported by Gantz et al. (2009) in their description of the results for the 87 recipients of the Hybrid S8 implant.
20. Wait a minute, are you saying that preservation of cochlear function does not affect the speech perception outcomes for the Hybrid/EAS recipients?
Thus far, that is what the data have shown. These findings, however, could be confounded by the metrics that were used. I'd like to go into it more, but it will take some time, and I see you just used up your 20th Question. How about we pick up this discussion at another time, as I'm sensing you're not quite finished with questions.
As you readers can tell, the topic of Hybrid/ EAS cochlear implants is a fascinating one, and it doesn't sound like our 20Q "Question Man" is finished. Fortunately, Dr. Gifford has agreed to make a repeat visit next month, when we'll continue our discussion on this topic. If you have questions on this topic, just send them to 20Q@gusmueller.net and I'll pass them along to René.
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