20Q: Developments in Pediatric Amplification – Audibility, Mild Hearing Loss and More

From the Desk of Gus Mueller

You’ve probably all heard the standard mantra from most all medical disciplines related to pediatrics:  “Children are not simply small adults.”  Audiology is no exception.  There is a reason our group has individuals who define themselves as “pediatric audiologists,”  why some AuD programs have a pediatric track, why the American Board of Audiology offers a Pediatric Audiology Specialty Certification, and why, thanks to Jerry Northern, the AAA Foundation offers scholarships in pediatric audiology training.

The expertise of the pediatric audiologist covers several unique areas of diagnostics, treatment and management, but for now, we’ll just focus on amplification.  Without even getting into modifications of techniques and procedures that might be needed, the fundamental rules for fitting hearing aids to the pediatric patient can be quite different than what we apply for adults.  One of these areas is the appropriate aided audibility, which will be one of the topics discussed in this month’s 20Q from our guest author Ryan McCreery.

Providing appropriate aided audibility for adults has been a popular theme here at 20Q lately.  In June, Anu Sharma presented evidence showing how the use of hearing aids can reverse unwanted cortical cross-modal re-organization, in July Ron Leavitt reported on how simply ensuring that appropriate aided audibility is present will provide large advantages in speech-in-noise understanding, and last month (September), the audibility issue also was discussed relative to the new APSO hearing aid fitting standard.  But all that was focused on adult patients—you now get to hear from one of the leading experts regarding how this relates to the pediatric population.

Ryan McCreery, PhD, is the Director of Audiology at Boys Town National Research Hospital in Omaha, Nebraska, a position that involves the strategic leadership of the 36 laboratories and 7 Centers that comprise the Boys Town Research program.  Dr. McCreery is also Director of the Audibility, Perception, and Cognition Laboratory. As most of you know from his many publications and presentations, his current research is advancing our understanding of the importance of auditory experience, including optimal hearing amplification in kids with hearing loss, for the proper development of language. 

Over the past years, Ryan has been involved with most all things audiologically pediatric, including large multi-site grants and writing hearing aid fitting guidelines. He has received numerous honors and awards, including Fellow of the American Speech-Language-Hearing Association (ASHA).  He is chair of the Academy’s Research Initiatives Committee, and is Editor in Chief of the American Journal of Audiology.

The work in pediatric audiology from the Boys Town group has been highly respected for decades, and we’re fortunate to have Ryan take the time to give us an update of some of their latest thoughts and research findings.  The only negative was that we only were allowed 20 questions!

Gus Mueller, PhD
Contributing Editor

Browse the complete collection of 20Q with Gus Mueller CEU articles at www.audiologyonline.com/20Q

20Q: Developments in Pediatric Amplification – Audibility, Mild Hearing Loss and More

Learning Outcomes 

After reading this article, professionals will be able to:

• Explain how the degree of hearing loss can determine audibility in pediatric hearing aid fittings.
• Describe the influence of duration of hearing aid use in pediatric hearing aid outcomes.
• Discuss how real-ear measures impact audibility in pediatric hearing aid fittings.

Ryan McCreery

1. Haven’t we known about the importance of improving audibility with hearing aids for a long time? Is there really something new?

Yes, but there are some points we can refine.  Audiologists think a lot about audibility because that’s the main outcome when we fit hearing aids. The goal of prescriptive fitting formulae that we use for children, like the Desired Sensation Level (DSL; Scollie et al. 2005), is to make speech audible and keep the output of the hearing aid at safe listening levels. When I was working in the clinic fitting hearing aids many years ago, I would notice the aided Speech Intelligibility Index (SII; ANSI S3.5-1997) on my verification equipment, and I would have a lot of questions. How much audibility is enough to support speech and language development for this child? What SII value should I try to achieve? What do I do if I am matching the prescriptive targets and the SII still seems low?

2. I thought I was supposed to be asking you questions. Did you ever find answers to your questions about audibility?

Some of these questions have been answered and some have not, but we know a lot more about audibility than we did when I was working in the clinic. Thanks to research from our friends at Western University in Ontario, we have a normative range for the aided SII so clinicians can determine the level of aided audibility that is achievable for a child’s degree of hearing loss if the child is fitted to DSL targets (Bagatto et al. 2016; you can access the charts here). The normative range is even built into some verification equipment so that the expected level of audibility can be confirmed while the hearing aids are being fitted. Providing audibility for speech is probably one of the most important things that audiologists who fit hearing aids for children can do.

3. Is audibility really that important?

Yes. We have known for a long time that children can only develop spoken language if they have access to the acoustic cues that are important for understanding speech. My former colleague Mary Pat Moeller found that even when children with hearing loss received hearing aids and early intervention during infancy, that many of them were not developing fricative sounds that were beyond the bandwidth of their hearing aids (Moeller et al. 2007).

More recently, I was fortunate enough to get to work with Mary Pat and a whole team of researchers from the University of Iowa, Boys Town, and the University of North Carolina Chapel Hill to follow a large group of children with hearing loss as part of several longitudinal studies known as the Outcomes of Children with Hearing Loss (OCHL) Collaboration. We followed over 300 children with hearing losses in the mild to severe range for over 10 years to try to identify malleable factors that predict developmental risk and resilience.

4. What do you mean by malleable factors?

When you look at the field of research on developmental outcomes for children with hearing loss, there’s been a tremendous amount of work over many decades that examines factors like degree of hearing loss, the presence of additional disabilities beyond hearing loss, socioeconomic status, age of diagnosis of hearing loss, or the point when hearing aids were fitted. These are important considerations for clinicians who work with children with hearing loss, but there’s very little that can be done to modify them through changes in intervention. We cannot change whether a child with hearing loss has an additional disability or move their hearing loss from a severe to a mild degree. These factors are important, but they are not malleable. We wanted to identify malleable factors because doing so would allow audiologists and early interventionists who work with children with hearing loss to modify the child’s fitting or other aspects of the intervention process to improve outcomes. 

5. What about the timing of the hearing aid fitting or intervention?

Much of the early research that was used to justify the establishment of universal newborn hearing screening and early hearing detection and intervention (EHDI) programs was based on research that showed that children with hearing loss who were identified, fitted with hearing aids, and enrolled in intervention at the earliest possible ages had better language outcomes than peers who received these intervention at later ages. We call these timing or duration variables because they are related to the timing of the child’s access to intervention, and if we are evaluating a child with hearing loss at a specific point in time, those timing variables can be used to quantify how long they have benefitted from the intervention. Some researchers and audiologists refer to this duration as “time in sound.” The challenge that we face in research now is that Universal Newborn Hearing Screening (UNHS) and EHDI programs have lowered the age of identification to around 3 months, and the age of hearing aid fitting to around 7 months (Holte et al. 2012). But, we still see considerable variability in language outcomes. The auditory experience that children receive from the time they are fitted or enrolled in intervention is not constant, and we have been trying to examine the malleable factors after hearing aids are provided that can improve outcomes.

6. What were the malleable factors that you considered?

The research team included a wide range of scientists and clinicians with expertise in audiology, child language, and psychology, and each member of the team had ideas for what the malleable factors might be. However, there were three consistent factors that seemed to come up consistently: speech audibility, hearing aid use, and the child’s language environment.  I’m not an expert on the child’s language environment, so I won’t get into that and disappoint my undergraduate professors in speech-language pathology. Audibility and hearing aid use were two of the malleable factors that the team identified and studied that are incredibly relevant for clinical audiologists because we can influence both through the work we do with children with hearing loss and their families. 

7. When we are measuring aided audibility, isn’t most of that related to the child’s degree of hearing loss?

The amount of audibility that can be provided through a hearing aid is definitely related to the child’s degree of hearing loss, which as we discussed is not something the audiologist can change. If you look at the normative range for the SII that I mentioned earlier, the amount of audibility that can be achieved by matching DSL targets decreases as the child’s degree of hearing loss increases. This is simply related to the fact that the residual dynamic range gets smaller as the degree of hearing loss increases and the fact that the SII has a level distortion factor that effectively reduces audibility above a certain level based on observations from adults with hearing loss.  However, we think about aided audibility as being malleable because the other component of the calculation is how well the hearing aid is fitted to prescriptive targets. More than half of the children we followed as part of the OCHL Collaboration had fittings that deviated from prescriptive targets by more than 5 dB averaged across 500 – 4000 Hz (McCreery et al. 2015). That was disappointing because it means that many children with hearing loss are walking around with hearing aids that are not optimized to provide adequate audibility. However, we also view it as an opportunity to improve hearing aid fitting for children, just like two decades ago when we realized we needed to lower the age of identification.

8. What can audiologists do to make sure that the children they fit with hearing aids have adequate audibility?

Using real-ear or simulated real-ear verification measures with an appropriate real-ear-to-coupler difference (RECD) to measure the aided audibility that the child has access to through their hearing aids is the only way to ensure that the fitting provides adequate audibility for speech. Aided audibility for speech cannot be derived from measuring an aided audiogram because the pure-tone stimuli and threshold levels used for those measures are not processed by the hearing aid in the same way as a broadband speech signal at an average level. In one of our studies, we found that audiologists that used appropriate real-ear verification measures with children had fittings that were closer to prescriptive targets and provided better audibility than audiologists who did not use these verification techniques (McCreery et al. 2013).

9. How close to prescriptive targets does the fitting need to be, ideally?

In our previous research, we have used a criterion that the root-mean-square (RMS) error of the fitting from prescriptive target should be <5 dB from 500 Hz – 4000 Hz. Many pediatric audiologists have let me know that they feel that this criterion is not ideal or reflective of best practices and that they would never allow a child to walk out of their clinic with a fitting that was 5 dB from targets across the range of frequencies that are most important for communication. I have to remind them that our research team didn’t fit the kids in the study or manage their hearing aids, so we used this criterion to allow a little more leniency in the event that the child’s ear canal had grown, the earmold didn’t fit as well, or their hearing had changed since the audiologist saw them. Even with that forgiving criterion, more than half the children in the study didn’t have fittings that met that standard.  In our own clinics, we recommend that the fitting be within +/- 3 dB of prescriptive targets for 500 Hz – 4000 Hz. This is not always possible because of sloping configurations or limitations of hearing aid bandwidth at higher frequencies, but we think it’s a reasonable goal. We are preparing a publication that examines whether using a +/- 3 dB criterion gives us better speech recognition and language outcomes than the +/- 5 dB criterion.

10. You also mentioned hearing aid use as an important malleable factor. What influence does this have on outcomes?

Before we started our longitudinal study, there was an assumption that children wore their hearing aids most of the time or all waking hours because as audiologists, that’s what we tell parents to do for their children. My colleague Beth Walker from the University of Iowa has published a series of papers (Walker et al. 2013; Walker et al. 2015) that showed that many families have difficulties establishing full-time hearing aid use, particularly during infancy and toddlerhood. Those of us on the project who have had or been around young children were not surprised by this. The good news is that the parents in our research study gave reports of average hearing aid use that were within two hours of the average data logging estimates generated by the hearing aids, so we believe that parents are generally accurate in their estimates of hearing aid use. There were some larger discrepancies for some parents who reported full-time use, when we observed that the data logging only showed a few hours/day.

11. Why do you think those parents were overestimating the amount of hearing aid use by that much?

Audiologists often tell families that their child should wear their hearing aids all waking hours to promote the best outcomes. This recommendation comes from a good place of wanting the child to have the most possible auditory access, but our hearing aid use data show that most families do not achieve all waking hours even as their children get older and consistent hearing aid use increases. My interpretation of these discrepancies is that parents are telling audiologists what they think we want to hear because they do not want to feel like they are failing their children. This finding has changed the way I talk to families about hearing aid use. Rather than all waking hours, it might be more helpful to ask about successes and challenges with hearing aid use and use the successes as building blocks for those more challenging situations. We don’t have any evidence to suggest that children with hearing aids need to wear their hearing aids all waking hours to have positive outcomes with their hearing aids, so I have stopped suggesting that as the goal.

12. How much do children need to wear their hearing aids if not all waking hours?

We have some interesting data from a paper published by Bruce Tomblin and our team (2015) that examined language growth for children divided into groups based on their hours of hearing aid use. The analysis showed that children who wore their hearing aids more than 10 hours per day had language growth curves that were closing the gap with peers with normal hearing, but did not find any additional benefits to language growth for children who wore their hearing aids more than 10 hours per day. This is only one study, but I think it supports the idea that hearing aid use is important, but that children may not need to wear their hearing aids all waking hours to experience growth in spoken language skills. 

13. How should audiologists counsel families who are struggling with hearing aid use?

I think as audiologists we want to focus on letting families know that hearing aid use is challenging, particularly for infants and young children. However, the challenge is worth facing if they want their child to develop spoken language. I think we should also focus our counseling more on quality time vs. the quantity of time that children are wearing their hearing aids. I tend to focus on having parents focus on establishing hearing aid use for times during the day when there’s a lot of communication going on and creating an environment that limits extraneous sources of background noise whenever possible. If a family is struggling with hearing aid use, being supportive and setting realistic goals can be helpful as well.

14. What about children with mild hearing loss?

Hearing aid use is very important, even for children with milder degrees of hearing loss. Children with mild bilateral hearing loss are less likely to obtain hearing aids and have fewer average hours of hearing aid use than peers with greater degrees of hearing loss (Walker et al. 2013). We also found that children with mild bilateral hearing loss who wore their hearing aids consistently had better language outcomes than children with mild bilateral hearing loss who did not consistently wear their hearing aids. This highlights one of the other main observations across the OCHL Collaboration, which has been that children with mild bilateral hearing loss are falling behind peers with normal hearing and in some cases have poorer outcomes than children who have moderate or greater degrees of hearing loss. 

15. Why do you think children with mild bilateral hearing loss seem to be at greater risk in some cases?

The fact that we refer to the category of hearing loss as mild is problematic because it suggests that it’s a degree of hearing loss that is unlikely to have significant negative consequences. However, we have known for a very long time that mild hearing loss is a developmental risk. Julia Davis at the University of Iowa published a paperback in 1986 where the children with mild hearing loss had similar language outcomes as children with moderate losses. There’s also ambivalence among audiologists about whether to fit children with mild hearing loss with hearing aids or wait to see if problems emerge before intervening. This “failure-based model” (Winiger et al. 2016) is not effective because we often have significant delays in language or academics before intervention is provided. 

16. How do you know audiologists are hesitant to fit children with mild bilateral hearing losses?

In our own data, we see children with mild bilateral hearing loss who have a range of possible interventions provided to them by different audiologists. Some obtain hearing aids at the point of identification like children with greater degrees of hearing loss, but then there are others, who never get amplification even with an early diagnosis. In other cases, hearing aids are fitted much later than the initial diagnosis. There seems to be a lot of uncertainty for children who have audiograms with pure-tone averages less than 30 dB HL in the better-ear where the probability that the child will receive a hearing aid in a timely manner decreases as the PTA gets better.

17. What do you suggest as an alternative approach?

We think children with mild bilateral hearing loss should be fitted with hearing aids as soon as hearing loss is diagnosed, but audiologists are clearly still hesitant because it’s unclear what level of hearing is associated with risk for language problems. To help address that, we studied the language outcomes for children with hearing loss in the study regardless of whether they received hearing aids or wore them consistently. As a result, we had data from a group of children with varying degrees of hearing loss who never wore amplification. This allowed us to examine the relationship between unaided hearing and language outcomes in a way that would not have been ethical in a planned, prospective study. What we found is that children with an unaided SII < 80 had language outcomes that were poorer than peers with normal hearing (McCreery et al. 2020). To give you a rough idea of how this might translate to the audiogram, a 3-year-old child with normal hearing in the lows that then drops to 30 dB at 2000, 3000 and 4000 Hz will have an SII around 80.

18. So it might be possible for audiologists to use the SII to help with decisions about hearing aid candidacy?

Calculating the unaided SII involves taking the audiogram and converting it to dB SPL to estimate how much of the long-term average speech spectrum is audible without a hearing aid. Clinical hearing aid verification systems and some audiometers will calculate this automatically just by entering the audiogram. The benefit of using the SII over the dB HL audiogram is that the conversion to dB SPL accounts for individual differences in ear-canal acoustics that can affect our threshold measurements for children.

19. I’m familiar with how the RECD affects hearing aid verification, but how does it impact thresholds?

The dB HL audiogram for insert earphones is referenced to a 2cc coupler that is designed to mimic the volume of an average adult ear canal. If the volume in the ear canal with an insert is less the 2cc, as it is for most children and even some adults, the sound pressure level in that space will be higher than it was in the 2cc coupler because of acoustics. For infants and young children with small ear canals, they get an enhancement of the sound level in the ear canal when we test them that is not apparent from the dB HL audiogram. When we convert to dB SPL, we can account for the ear-canal acoustics via the RECD and see that many of the children we thought had mild degrees of hearing loss have significant audibility deficits that could impact their speech and language development. Using the unaided SII for hearing aid candidacy also allows for a direct comparison to the aided SII when we fit a hearing aid to see the increase in audibility that is provided over the unaided condition in each ear. 

20. That’s all very fascinating work. What are the new research projects that you have underway related to pediatric amplification?

We recently started a new project to develop clinical tools for audiometry and speech recognition that will be more sensitive to the challenges faced by children with mild bilateral hearing loss. We know that children often make noise during hearing assessment, and we are developing a way to quantify that noise and the impact on audiometry to improve the accuracy of our tests. We are also working as part of a multi-site consortium to develop a speech recognition test that can be given in either English or Spanish, regardless of whether the audiologist speaks Spanish. That test is called Chegss and is currently undergoing clinical validation at multiple pediatric audiology clinics around the US.  We have also started a collaboration with a neuroscientist, Dr. Elizabeth Heinrichs-Graham, to study how audibility and hearing aid use impact the structure and function of the brain. I can’t imagine a better time to be a pediatric audiologist. 

References

Bagatto, M., Moodie, S., Brown, C., Malandrino, A., Richert, F., Clench, D., & Scollie, S. (2016). Prescribing and verifying hearing aids applying the American Academy of Audiology pediatric amplification guideline: Protocols and outcomes from the Ontario infant hearing program. Journal of the American Academy of Audiology, 27(3), 188-203.

Davis, J. M., Elfenbein, J., Schum, R., & Bentler, R. A. (1986). Effects of mild and moderate hearing impairments on language, educational, and psychosocial behavior of children. Journal of Speech and Hearing Disorders, 51(1), 53-62.

Holte, L., Walker, E., Oleson, J., Spratford, M., Moeller, M. P., Roush, P., ... & Tomblina, J. B. (2012). Factors Influencing Follow-Up to Newborn Hearing Screening for Infants Who Are Hard of Hearing. American Journal of Audiology, 21, 163-174.

McCreery, R. W., Bentler, R. A., & Roush, P. A. (2013). Characteristics of Hearing Aid Fittings in Infants and Young Children. Ear and Hearing, 34(6), 701-710.

McCreery, R. W., Walker, E. A., Spratford, M., Bentler, R., Holte, L., Roush, P., ... & Moeller, M. P. (2015). Longitudinal Predictors of Aided Speech Audibility in Infants and Children. Ear and Hearing, 36(0 1), 24S-37S.

Moeller, M. P., Hoover, B., Putman, C., Arbataitis, K., Bohnenkamp, G., Peterson, B., ... & Stelmachowicz, P. (2007). Vocalizations of infants with hearing loss compared with infants with normal hearing: Part I–phonetic development. Ear and Hearing, 28(5), 605-627.

Scollie, S., Seewald, R., Cornelisse, L., Moodie, S., Bagatto, M., Laurnagaray, D., ... & Pumford, J. (2005). The desired sensation level multistage input/output algorithm. Trends in Amplification, 9(4), 159-197.

Walker, E. A., Spratford, M., Moeller, M. P., Oleson, J., Ou, H., Roush, P., & Jacobs, S. (2013). Predictors of Hearing Aid Use Time in Children with Mild-to-Severe Hearing Loss. Language, Speech, and Hearing Services in Schools, 44(1), 73-88.

Walker, E. A., McCreery, R. W., Spratford, M., Oleson, J. J., Van Buren, J., Bentler, R., ... & Moeller, M. P. (2015). Trends and Predictors of Longitudinal Hearing Aid Use for Children Who Are Hard of Hearing. Ear and Hearing, 36, 38S-47S.

Winiger, A. M., Alexander, J. M., & Diefendorf, A. O. (2016). Minimal hearing loss: From a failure-based approach to evidence-based practice. American Journal of Audiology, 25(3), 232-245.