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Hearing Journal:
doi: 10.1097/01.HJ.0000436554.87379.67
Journal Club

Journal Club: NLFC in Bimodal Hearing: Getting Research Up to Speed

Gifford, René H. PhD

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Dr. Gifford is director of the cochlear implant program, associate director of pediatric audiology, and assistant professor of hearing and speech sciences at the Vanderbilt Bill Wilkerson Center in Nashville.

Pediatric audiologists are often torn between two goals—being aggressive enough in their recommendations for habilitation to ensure that each child has the audibility needed to develop speech, language, and literacy at age-appropriate levels, and making certain that the least invasive treatment options are fully investigated.

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The latter objective is particularly important in cases of cochlear implantation, as the decision is an irreversible one.

Although bilateral cochlear implantation is considered the standard of care for adults and children with severe-to-profound sensorineural hearing loss, families with children undergoing cochlear implantation for asymmetric hearing loss or less severe degrees of hearing loss are often counseled to consider a single cochlear implant combined with a hearing aid on the better hearing ear.

Ren H. Gifford, PhD...
Ren H. Gifford, PhD...
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This recommendation is primarily based on research evaluating outcomes with bimodal hearing in adult cochlear implant recipients (e.g., J Speech Lang Hear Res 2006;49[2]:338-351http://jslhr.asha.org/cgi/content/abstract/49/2/338; J Speech Lang Hear Res 2007;50[4]:835-843http://jslhr.asha.org/cgi/content/abstract/50/4/835; Audiol Neurotol 2008;13[2]:105-112http://www.karger.com/Article/FullText/111782).

There have been studies demonstrating benefits of the combined use of a cochlear implant and a contralateral hearing aid in children (J Acoust Soc Am 2010;128[4]:1884-1895http://asadl.org/jasa/resource/1/jasman/v128/i4/p1884_s1?isAuthorized=no; Indian J Otolaryngol Head Neck Surg 2010;62[4]:342-345; Audiol Neurotol 2010;15[1]:44-56http://www.karger.com/Article/FullText/219487). However, these young patients depend more on bottom-up processing than do postlingually deafened adults, for whom the objective differences between bimodal hearing and bilateral implantation may not be as evident.

In fact, in a study of bimodal and bilaterally implanted children, Mok et al concluded that while the degree of benefit obtained from a contralateral hearing aid was greater than that obtained from a second implant, the second cochlear implant “may provide more functional advantage in real life” (Audiol Neurotol 2010;15[1]:44-56http://www.karger.com/Article/FullText/219487).

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IDENTIFYING THE GAPS

In recent years, we have had at our disposal hearing aids equipped with nonlinear frequency compression (NFC) and frequency transposition capabilities. This technology holds promise for providing greater symmetry across implanted and non-implanted ears, both in audibility and speech recognition performance.

This month's Journal Club will review recent literature on outcomes in adults and children using a cochlear implant and contralateral hearing aid with nonlinear frequency compression.

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The Contribution of a Frequency-Compression Hearing Aid to Contralateral Cochlear Implant Performance

Perreau AE, Bentler RA, Tyler RS J Am Acad Audiol 2013;24(2):105-120

Perreau and colleagues investigated the bimodal benefit of conventional amplification versus a frequency-compression hearing aid. They used Phonak Naida IX SP or Naida V UP hearing aids, with and without SoundRecover.

SoundRecover was set using a modified fitting formula, SoundRecover Fitting Assistant v. 1.05, which fit the bandwidth of compression within the participant's audible region using the highest cutoff frequency and lowest compression ratio (Paper presented at the American Speech–Language–Hearing Association Convention; Nov. 20, 2009; New Orleans).

Hearing aids were verified with probe-microphone measures to ensure that audibility matched NAL-NL1 prescriptive targets. The researchers were also careful to ensure that loudness was balanced across ears.

Inclusion criteria required participants to have a moderate-to-severe hearing loss in the non-implanted ear and no experience with nonlinear frequency compression prior to study enrollment. They were given two months to use NFC in a daily alternating method of adjustment, spending one day with conventional amplification and the next with NFC.

Perreau et al assessed 10 listeners on objective measures of spondee recognition in noise and localization, as well as subjective measures of benefit, and 17 listeners on measures of vowel and consonant recognition.

For localization, consonant recognition, and subjective assessment on the spatial hearing questionnaire (Ear Hear 2009;30[4]:466-474http://journals.lww.com/ear-hearing/pages/articleviewer.aspx?year=2009&issue=08000&article=00009&type=abstract), there were no significant differences between bimodal hearing with NFC and without NFC.

Considering subjective estimates of speech understanding on the sound quality questionnaire (Ear Hear 2009;30[4]:466-474http://journals.lww.com/ear-hearing/pages/articleviewer.aspx?year=2009&issue=08000&article=00009&type=abstract), however, participants reported significantly higher ratings for bimodal hearing without NFC.

On measures of vowel recognition—for which spectral resolution is critical—and spondee recognition in noise, bimodal listeners also scored significantly higher using conventional amplification without NFC.

Thus, the authors concluded that adult bimodal listeners do not derive benefit from the use of nonlinear frequency compression in the contralateral hearing aid and that in some listening conditions, the use of NFC in the non-implanted ear may actually degrade performance.

Communication involves multisensory processing, including running speech with contextual clues. Thus, it is possible that everyday communication may not be negatively affected by poorer vowel recognition with nonlinear frequency compression. Clearly, though, we wouldn't want to fit our bimodal patients with a technology that has the potential to yield poorer performance than conventional amplification.

Despite the rigorous experimentation described in the study by Perreau and colleagues, more research is needed to investigate not only sentence recognition, in context, but also listening effort with and without NFC in a bimodal hearing configuration.

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An Evidence-Based Systematic Review of Frequency Lowering in Hearing Aids for School-Age Children with Hearing Loss

McCreery RW, Venediktov RA, Coleman JJ, Leech HM Am J Audiol 2012;21(2):313-328

In a remarkably thorough review article, McCreery and colleagues outlined the results of five prior studies investigating the effectiveness of frequency-lowering technology, including nonlinear frequency compression, frequency transposition, and a combination of frequency compression and temporal envelope enhancement to aid consonant recognition.

Studies have demonstrated the superiority of nonlinear frequency compression for recognition of plurality in school-age children wearing hearing aids, McCreery and colleagues explained (see Int J Audiol 2009;48[9]:632-644http://informahealthcare.com/doi/abs/10.1080/14992020902971349; J Am Acad Audiol 2010;21[10]:618-628http://www.ncbi.nlm.nih.gov/pubmed/21376003; Intl J Audiol 2011;50[6]:396-404http://informahealthcare.com/doi/abs/10.3109/14992027.2010.551788).

Correct identification of plurality is crucial for morphological awareness, which in turn affects literacy skills. Plurality recognition is also an important skill for speech understanding, even in the presence of contextual and visual cues.

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PRACTICE OUTPACES RESEARCH

What is missing in the literature is a carefully controlled study of the effects of nonlinear frequency compression and other methods of frequency lowering in pediatric bimodal users with various types and degrees of hearing loss.

Christine Jones, AuD, and Stefan Launer, PhD, reported that SoundRecover, or NFC, is activated in approximately 80 percent of Phonak pediatric hearing aid fittings (Pediatric Hearing Instrument Fitting in 2010: The Sound Foundations Cuper Projecthttp://www.phonakpro.com/content/dam/phonak/b2b/Events/conference_proceedings/soundfoundation_chicaco2010/pdf/SoundFoundation_Chicago2010_Jones.pdf). Because the use of nonlinear frequency compression has become so clinically prevalent in children with a bimodal hearing configuration or bilateral hearing aids, further research is essential to ensure that our clinical decisions are data driven.

In the meantime, the current literature base suggests that the use of NFC likely will “do no harm” to the speech-understanding abilities of adult bimodal listeners (in the presence of contextual cues) and pediatric hearing aid users.

So long as we continue to follow recommended practices for our pediatric hearing aid and cochlear implant users, including real-ear measures for hearing aid fittings, sound-field-aided detection thresholds for cochlear implants, administration of parental questionnaires for tracking auditory progress, and speech recognition testing using standardized measures at average conversational levels, we will be doing our best to provide the greatest access to sound, ensuring speech, language, academic, and social success for children with hearing loss.

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References on Tap

Access the hyperlinks (shown in gray) in this article and throughout the issue by reading it on HJ's free iPad app: bit.ly/AppHearingJ.

© 2013 by Lippincott Williams & Wilkins, Inc.

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