20Q: Outcomes of Children with Cochlear Implants - Shooting for the Moon!

From the Desk of Gus Mueller

Like all professional disciplines, we’re always looking for progress in our field of clinical audiology. But some things move slowly - take audiologic diagnostics, for example. Does the average clinician do more definitive tests today than they did ten years ago? Twenty years ago? And how about hearing aid fittings with adults? Granted, we’ve seen huge improvements in feedback reduction and connectivity, but how about the basic need to improve speech understanding in background noise? Better today than it was ten years ago? Twenty years ago?

There is one area, however, where progress has been very obvious and measureable in the recent past—outcomes for young children receiving cochlear implants. We have seen numerous research studies that have explored various outcomes of children with cochlear implants, and also investigation into what factors impact these outcomes. The findings are very encouraging. The results of these studies have suggested that excellent listening, spoken language, and literacy outcomes are possible for most children with cochlear implants when a handful of important factors are satisfied. In this month’s installment of 20Q, we’ll examine several recent research studies that have explored these outcomes and the related factors.

We have with us one of the leading experts on this topic, Jace Wolfe, PhD, Director of Audiology and Research at the Hearts for Hearing Foundation in Oklahoma City, OK. Dr. Wolfe also is an adjunct Assistant Professor in the Audiology Department at the University of Oklahoma Health Sciences Center and Salus University.

You might know Dr. Wolfe for his previous articles here at AudiologyOnline, or his frequent columns published in The Hearing Journal titled “The Tot Ten.” His prolific work also has resulted in several textbooks. He is author of the book entitled “Cochlear Implants: Audiologic Management and Considerations for Implantable Hearing Devices,” and is co-editor of the books “Pediatric Audiology: Diagnosis, Technology, and Management, Third Edition” and “Pediatric Audiology Casebook, Second Edition.” He is also a co-author of the textbook entitled “Programming Cochlear Implants, Second Edition.”

Dr. Wolfe is a member of the Better Hearing Institute’s Pediatric Advisory Board as well as the Audiology Advisory Boards for Cochlear Americas, Advanced Bionics, and the Phonak Hearing Aid Company.

In this 20Q article, Jace mentions the notion of “shooting for the moon.”  As you read his excellent review of what has been accomplished in the area of cochlear implants, and the outcomes that we are now seeing, you just might conclude that while we are not there yet, we are much closer to the moon than we ever thought we would be.

Gus Mueller, PhD
Contributing Editor
 

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

20Q: Outcomes of Children with Cochlear Implants - Shooting for the Moon!

Learning Outcomes 

After this course, readers will be able to:

• List key research papers on outcomes of children with CIs.
• Explain how age at implantation may impact outcomes for children with CIs.
• Discuss candidacy considerations for CIs in children.
• Discuss how the following factors may impact outcomes in children with CIs: auditory-based therapy, communication mode, maternal education, medical and developmental issues.

Jace Wolfe

1. Shooting for the moon?

Norman Vincent Peale, author of the motivational book entitled, The Power of Positive Thinking, once said, “Shoot for the moon. Even if you miss, you’ll land among the stars.” Although that quote might not be astronomically correct ((the moon is a mere 93 million miles away from its closest star, the sun), you get the idea. If we set our sites high, we are more likely to achieve success in life. That adage certainly applies to the outcomes achieved by children with cochlear implants. A host of recent research studies have explored the outcomes of children with cochlear implants along with the factors that influence the outcomes children achieve with cochlear implants.

2. So there are things we can learn from these recent studies?

Absolutely! There have been several papers describing the results of some exceptionally important cochlear implant outcomes studies, and there are several relevant lessons we can learn to improve the outcomes of children with cochlear implants. Three great sources of information are the Australian Longitudinal Outcomes of Children with Hearing Impairment (LOCHI) study, the Childhood Development after Cochlear Implantation (CDaCI) study, and a series of studies completed by researchers at the University of Melbourne. The LOCHI and CDaCI studies are unique and relevant because both are large, NIH-funded, population-based research initiatives that prospectively examine the outcomes of children who receive cochlear implants with serial assessments administered prior to and at several points across many years following cochlear implantation. Of note, the LOCHI study also includes children who are hard of hearing and use hearing aids. The Melbourne research is pertinent because it takes a close look at the influence of age at implantation on a variety of outcomes for a large number of children (i.e., over 400 kids) who received cochlear implants prior to 6 years of age.   

3. Those all sound like great studies! Where should we start?

Let’s start with the importance of age at implantation, because that is a variable that we can often control and one that has been found to have a substantial impact on the outcomes of children with cochlear implants. Teresa Ching and her LOCHI colleagues (2013) have reported on language outcomes measured at 3 and 5 years of age for a group of over 110 children with cochlear implants. They found that when the children were three years old, age at implantation was one of the most important factors influencing language progress. Specifically, delaying implantation from 6 months to 12 months of age resulted in an approximately ½ standard deviation decrease in language progress (i.e., an almost 8-point reduction in the mean score for a standardized measure of language ability). Continued delays in implantation beyond 12 months of age resulted in similar reductions of language delay. At five years of age, Ching and colleagues (2018) reported that earlier implantation was once again associated with significantly better expressive and receptive language, speech production, and speech perception. In short, children who received cochlear implants prior to 12 months of age achieved significantly better listening and spoken language outcomes.

4. What type of outcome should I expect for children who receive a cochlear implant prior to their first birthday?

New research coming out of the University of Melbourne is suggesting that the sky is the limit for children who receive their cochlear implants during the first year of life (Dettman et al., 2016). Shani Dettman and colleagues in Melbourne examined listening and spoken language outcomes for 403 children at school-age entry (e.g., 5 to 6 years old), 151 of whom were implanted prior to 12 months of age, 61 implanted between 13 to 18 months of age, 66 implanted between 19-24 month of age, and 125 implanted after their second birthday. Remarkably, 81% of the children who received an implant prior to 12 months of age achieved age-appropriate vocabulary levels (e.g., mean standard score of 99.8 on the Peabody Picture Vocabulary Test) at school-age entry! In contrast, only 52% of children implanted between 13 to 18 months of age achieved normal vocabulary development (mean standard score = 82.9), and less than 25% of children implanted after 18 months of age achieved normal vocabulary scores (e.g., mean standard score of 65.4 for children implanted between 19 to 24 months of age).

5. Powerful findings! Were there other differences in outcomes obtained among the different groups of children?

Yes, the children who were implanted prior to 12 months of age achieved better speech perception, speech production, and expressive and receptive language when compared to children who received implants after 12 months of age. Additionally, the majority of children who received cochlear implants before their first birthday achieved age-appropriate listening and spoken skills, whereas the overwhelming majority of children implanted after 12 months had language outcomes that were outside the normative range. In short, the results of the Dettman and colleagues (2016) study suggest that normal listening and spoken language abilities are not only possible but instead, are probable when children receive cochlear implants during the first year of life. Of note, current United States FDA guidelines, which have not changed for almost 20 years, call for a minimum age for implantation of 12 months. Pediatric audiologists, researchers, and cochlear implant manufacturers should work with the FDA to revise indications of use pertaining to age at implantation.  

6. Is there any research that identifies the ideal age at which a child should receive a cochlear implant?

Yes, the Melbourne group has tackled this question as well. In a separate study, Jaime Leigh and colleagues (2016) sought to identify the ideal age at which a child should receive a cochlear implant. They measured language development in 32 children who received their first cochlear implant prior to 2.5 years of age. They reported that children with severe to profound hearing loss made 0.3 years of language growth in one calendar year prior to implantation and 1.03 years of language growth after cochlear implantation. As a result, children who were implanted at 6 months of age had little to no language delay and achieved age-appropriate language development after implantation. Stated differently, their language abilities never fell behind those of their normal-hearing peers. In contrast, children implanted at later ages exhibited language delays that roughly mirrored the age at which they received their cochlear implants. For instance, children who received a cochlear implant at 18 months of age had an almost one-year language delay at the time of implantation, and approximately a one-year language delay thereafter.

7. Did the Melbourne researchers recommend an ideal age of implantation?

They did! Leigh and colleagues (2016) stated their study results “suggest that if a child receives a cochlear implant before 2.5 years, they have the potential to make age-appropriate language progress. They will, however, demonstrate a language delay closely related to their age at implantation. This result provides compelling evidence that a cochlear implant should be offered as young as possible to minimize this language delay as long as the child meets audiological guidelines and other medical issues have been considered.” 

The Melbourne group also examined how the 2.5 year time frame might impact word recognition. Leigh and colleagues (2016) compared aided Phonetically Balanced Kindergarten (PBK-50) word recognition scores for 78 children who received their first cochlear implant prior to 2.5 years of age and 62 children who used hearing aids and had sensorineural hearing loss ranging from mild to profound. Leigh et al. found that children with a pure tone average (500, 1000, and 2000 Hz) of 60 dB HL in the better hearing ear had a 75% chance of achieving better word recognition with a cochlear implant relative to their performance with hearing aids. Children with a 75 dB HL pure tone average had almost a 90% likelihood of better aided word recognition with a cochlear implant compared to a hearing aid. In short, the Melbourne data suggest that speech perception of children with severe hearing loss is likely to better with a cochlear implant than a hearing aid.    

8. It sounds like a larger population of children could benefit than I expected. So, do I base the decision to recommend a cochlear implant solely on the audiogram?

No. Although new research may be changing the way we provide intervention for children with hearing loss, the cross-check principle described by Drs. James Jerger and Deborah Hayes in 1976 is just as relevant as ever in the decision to recommend a cochlear implant for a child. The tone-burst-elicited auditory brainstem response is the best measure for estimating behavioral hearing thresholds. Research out of the University of North Carolina provides strong evidence that children should be considered for cochlear implantation when their ABR is consistent with profound hearing loss (Hang et al., 2015). Additionally, the audiologist should also administer questionnaires to evaluate functional auditory performance (e.g., LittlEARS, PEACH, etc.) to confirm that the child is showing limited auditory responsiveness in real-world situations. Furthermore, the audiologist should consider completing unaided behavioral audiologic assessment. Although children with hearing loss cannot provide reliable threshold-level responses until they are able to participate in visual reinforcement audiometry (e.g., 7-9 months of age), behavioral audiologic assessment may be administered to ensure that the child is not producing auditory responses at levels that are better than what is suggested by ABR assessment. Finally, the audiologist should maintain close dialogue with the child’s parents and speech-language pathologist (e.g., listening and spoken language specialist) to ensure that the child is making limited progress in listening and spoken language development with the use of hearing aids.

9. Great advice! Are there any other benefits of early implantation?

Quite possibly! The Melbourne group recently reported on another surprising finding related to early implantation. Chu and colleagues (2016) examined the effect of the “dosage” of intervention on language outcomes. Essentially, dosage refers to the amount of therapy a child with a cochlear implant received during the first few years of life. You might be surprised to learn that children who received therapy on a monthly basis achieved better language outcomes at school-entry age (e.g., 5 to 6 years old) than children who received therapy on a weekly or bi-weekly basis.

10. That makes no sense! Was therapy harmful to language development? And what does that finding have to do with early implantation?

First off, therapy is not detrimental to language outcomes. Upon further inspection, Chu et al. (2016) discovered that the children who received therapy on a monthly basis were more inclined to have received their cochlear implants prior to 12 months of age. Consequently, they never developed a significant language delay, and frequent, intensive therapy was not necessarily imperative. In contrast, the children who received more frequent therapy were more likely to have received their cochlear implants after 12 months of age. As a result, they had developed language delays by the time of implantation and were in need of intensive therapy to eliminate/ameliorate the delays. So, another benefit of implantation prior to 12 months of age is the possibility that less intervention will be required to achieve age-appropriate listening and spoken language development. Indeed, the best outcome likely will be obtained when children receive cochlear implants before 12 months of age and also receive excellent auditory-based therapy.

11. Got it! What other factors can influence the outcome?

There are several, but let’s start with communication mode. The LOCHI study (Ching et al., 2013; 2018), the Melbourne group (Chu et al., 2016; Dettman, Wall, Constantinescu, & Dowell, 2013), and the CDaCI study (Geers et al., 2017) all examined the relationship between the outcomes of children with cochlear implants and the communication mode used by the child’s caregivers. Each of these research studies found better listening and spoken language outcomes for children whose families communicated through listening and spoken language compared to the outcomes of children whose families used sign language.

12. Were outcomes adversely affected if sign language was only used prior to cochlear implantation?

Ann Geers and her CDaCI colleagues (2017) actually explored that question. They examined spoken language and literacy outcomes for three groups of children who had an average age of implantation of just under 2 years of age: 1) No Sign Language: no use of sign language prior to or after implantation, 2) Short-term Sign Language: use of sign language prior to implantation and/or for up to 12 months after implantation, and 3) Long-term Sign Language: use of sign language prior to implantation and/or for at least 3 years after implantation. The authors reported better language and literacy outcomes for late-elementary age children in the no-sign group compared to both the short-term and long-term sign language groups. Geers concluded that “early exposure to sign language did not enhance spoken language or reading abilities. In fact, children whose parents signed were significantly more likely than children of non-signing parents to exhibit language delays and fall behind age-mates in reading comprehension.” Long-term use of sign language was associated with even greater delays.    

13. Did the researchers offer reasons for the better outcomes obtained by children whose families focused solely on listening and spoken language?

It is important to remember that 90-95% of children with hearing loss have parents who have normal hearing (Mitchell & Karchmer, 2004). Consequently, most parents of children with hearing loss are not fluent in sign language. When they communicate with their children through spoken and sign language, it is possible that they are reducing the number of words they are speaking in an attempt to pair spoken words with their limited sign language vocabulary. As a result, they may not be speaking as much to their children, and the language-rich listening environment modeled by the parents is not as robust as what would occur when parents communicate via the use of open-ended, expansive, complex spoken language. Accordingly, Geers and colleagues (2017) noted that “it is possible that use of sign language interfered with auditory and speech development.”

On the other hand, it is possible that the relationship between communication mode and language outcomes is one of association and not causality. For instance, it is possible that families whose children may satisfactory progress in listening and spoken language development discontinued the use of sign language whereas the families continued to communicate via sign language for children who struggled to progress after implantation. Moreover, it is possible that there are inherent differences between families and children who elect to use sign language and those who do not (e.g., maternal education levels, additional disabilities, income levels, etc.), and these differences may also serve to influence the outcomes children ultimately achieve. It should be noted, however, that the groups in the Geers et al. (2017) study were well-matched on several factors known to influence outcomes and also had similar auditory and vocabulary skills prior to implantation.  Nonetheless, better spoken language and literacy outcomes were found for the children whose families did not use sign language.

14. And you have more significant factors?

I do! It probably won’t surprise you to hear that all of the studies we have discussed so far have also concluded that “mom matters.” The LOCHI (Ching et al., 2013; 2018) study both found better outcomes for children whose mothers had higher levels of education (e.g., college education). The CDaCI researchers also reported that better language outcomes were associated with higher levels of maternal sensitivity (Markman et al., 2011). Likewise, the Melbourne researchers reported better language outcomes for children whose mothers were more involved with the care and intervention of their children (Chu et al., 2016). These findings may have occurred for several reasons. Mothers with higher levels of education may have greater resources to obtain the technology and services needed to optimize the outcomes of their children. Also, it is possible that mothers with higher levels of education provide a more robust linguistic model to which their children may be exposed to develop better listening and spoken language abilities. Whatever the reason, mothers play a big role in the outcomes of children with hearing loss. Abe Lincoln got it right when he said, “all that I am, or hope to be, I owe to my angel mother.” It is incumbent upon hearing healthcare professionals to engage, coach, and support the mothers of children with hearing loss to ensure that mothers are positioned to assist children in reaching their full potential after cochlear implantation.

15. You haven’t mentioned children with other disabilities. I assume that is a factor in all this research?

Yes it is. An important aspect of the LOCHI study is the fact that it explores outcomes of all children with hearing loss regardless of whether the children have additional disabilities other than hearing loss. Many research studies evaluating the outcomes of children with hearing loss only examine the progress of children who do not have additional disabilities. The LOCHI researchers reported that 37% of the children in their study had a disability (or disabilities) other than hearing loss, a prevalence that is in line with findings of other studies (Ching et al., 2018; Cupples et al., 2018; Gallaudet Research Institute, 2011; Picard, 2004). As one might expect, the LOCHI researchers reported poorer language outcomes for children who had multiple disabilities.              

16. Were there certain factors that impacted the outcomes achieved by children with multiple disabilities?

Children who had neurocognitive disabilities that are known to lead to developmental delay (e.g., autism, cerebral palsy, neurological deficits associated with CMV, etc.) were more likely to have poorer language outcomes than children with other types of disabilities (e.g., visual impairment, syndromes not entailing developmental delay, etc.; Ching et al., 2018; Cupples et al., 2018). Also, as one may expect, children with lower non-verbal IQs tended to exhibit poorer language outcomes. Encouragingly, children who have multiple disabilities and who received hearing technology at an early age (e.g., hearing aids, cochlear implants) tended to achieve better language outcomes, a finding that once again underscores the importance of early intervention. Furthermore, children whose mothers had higher educational levels obtained better outcomes. Again, hearing healthcare professionals must support families with limited resources to provide the support and care their children require to fulfill their full potential. Additionally, children with multiple disabilities tended to achieve better language outcomes when their families focused on listening and spoken language rather than the use of sign language, a finding that highlights the vital need to provide children with a robust audition-based linguistic model.

17. That’s a lot to process. I am uncertain that I can meet all of the needs of the child and family.

No hearing healthcare providers can meet every unique need of every child who has hearing loss and additional disabilities. Instead, we should strive to form collaborative, interdisciplinary relationships with other healthcare providers and educators who possess various expertise specific to the unique needs of the children we serve. For instance, we should routinely partner with neurodevelopmental specialists, speech-language pathologists, physical and occupational therapists, physicians, educators, etc. to provide holistic care that satisfies the comprehensive needs of the child and not just needs pertaining to hearing impairment. Teresa Ching of the LOCHI study (2018) summed it up best by saying that the finding of poorer outcomes for children with multiple disabilities “underscores the importance of establishing effective collaborations among professionals in the management of children with hearing loss who have additional disabilities in order to facilitate early (and effective) treatment for hearing loss” and optimize the outcome of each child.          

18. Any other interesting findings from these studies?        

Although the LOCHI, CDaCI, and Melbourne researchers have not reported extensively on the impact of temporal bone abnormalities on the outcomes of children with cochlear implants, it is an important area worth discussing. Several researchers have explored the impact of temporal bone abnormalities on the listening and spoken language outcomes of children with cochlear implants. For instance, Blake Papsin (2005) examined outcomes of 140 children with anomalous cochleovestibular anatomy and reported substantial improvement in speech perception for the vast majority of the study participants. Dr. Papsin did note that poorer outcomes were observed in children with common cavity cochleae and particularly for those with narrow internal auditory canals. Likewise, Buchman and colleagues (2004) studied outcomes of 28 children with inner era malformations and reported that the majority received “substantial” benefit from cochlear implantation and developed speech recognition abilities after receiving their cochlear implant. Buchman and colleagues noted exceptionally good benefit in children with a diagnosis of enlarged vestibular aqueduct but poorer benefit in children with common cavity cochleae, total aplasia of the semicircular canals, and complex diagnoses such as CHARGE, which may be associated with neurological deficits. Additionally, poorer outcomes are expected for children who have ossified cochleae after bacterial meningitis, a fact the emphasizes the importance of expeditious implantation so that an electrode array may be fully inserted into the cochlea prior to ossification. In summary, however, many children with inner ear abnormalities receive significant benefit from cochlear implants. Hearing healthcare providers should be cognizant of the impact of specific types of cochleovestibular abnormalities on post-implantation outcomes, and counsel the family accordingly. 

19. Could their reduced performance be attributed to a problem with the cochlear nerve?

You are probably right on target. Many children with cochlear abnormalities perform exceptionally well with cochlear implants, particularly when they receive their cochlear implants at an early age, use their cochlear implants during all waking hours, and receive excellent support from their caregivers who provide a robust language-rich listening environment. However, a fairly substantial body of literature has shown poorer outcomes for children who have been diagnosed with cochlear nerve deficiency, a term used to collectively describe cochlear nerve hypoplasia and cochlear nerve aplasia. According to Wu and colleagues (2015), cochlear nerve hypoplasia describes a condition in which MRI reveals the caliber of the cochlear nerve to have a smaller diameter than the adjacent facial nerve. Cochlear nerve aplasia is described as an absence of a cochlear nerve on an MRI. In general, listening and spoken language outcomes are poorer for children with cochlear nerve hypoplasia than children with normal cochlear nerve anatomy. However, some children with cochlear nerve hypoplasia do receive benefit from cochlear implantation and develop modest open-set speech recognition abilities (Birman, Powell, Gibson, & Elliott, 2016). As you probably expect, auditory and spoken language outcomes are likely to be poor for children with absent cochlear nerves. After a failed trial with a cochlear implant, these children may be considered for an auditory brainstem implant (ABI), although more research is needed to better understand the potential limitations and advantages and ABIs. Fortunately, Freeman and Sennaroglu (2018) estimate that only 2% of congenital profound hearing loss is attributed to cochlear nerve deficiency.

To briefly summarize, relatively poorer post-implant outcomes are likely for children with cochlear nerve deficiency, especially for those with absent cochlear nerves. However, some children with hypoplastic cochlear nerves do derive significant benefit from cochlear implantation and develop substantial auditory and spoken language abilities, especially when they receive excellent support from caregivers. Hearing healthcare professionals should provide careful counsel regarding realistic expectations to families of children with cochlear nerve deficiency. Moreover, families should consider use of sign language for children with cochlear nerve deficiency to ensure the child has access to language in the event that an auditory signal cannot be provided via the cochlear implant.     

20. Any take-home messages?

Sure! Excellent listening and spoken language outcomes are possible for today’s children who are born with severe to profound hearing loss. Modern cochlear implant technology and hearing healthcare services are sufficient to allow for age-appropriate speech, language, and listening outcomes, particularly when cochlear implants are provided before 12 months of age, children use their cochlear implants during all waking hours, and the children are exposed to a robust model of intelligible, complex spoken language. Hearing healthcare providers must roll up our sleeves and work with our interdisciplinary models to make certain we are providing additional and ample support for children with multiple disabilities and children from vulnerable home situations (e.g., low income, low education levels, etc.). With advances in technology and audiological services, we have what it takes - we just have to do what it takes. When we do, children with any degree of hearing loss can shoot for the moon! 

References

Birman, C.S., Powell, H.R.F., Gibson, W.P.F., & Elliott, E.J. (2016). Cochlear implant outcomes in cochlear nerve aplasia and hypoplasia. Otology & Neurotology, 37, 438-445.

Buchman, C.A., Copeland, B.J., Yu, K.K., Brown, C.J., Carrasco, V.N., & Pillsbury, H.C. (2004). Cochlear implantation in children with congenital inner ear malformations. The Laryngoscope, 114, 309-316.

Ching, T.Y., Dillon, H., Leigh, G., & Cupples, L. (2018). Learning from the longitudinal outcomes of children with hearing impairment (LOCHI) study: summary of 5-year findings and implications. International Journal of Audiology, 57(2), S105-S111.

Ching, T. Y., Dillon, H., Marnane, V., Hou, S., Day, J., Seeto, M., . . . Yeh, A. (2013). Outcomes of early- and late-identified children at 3 years of age: findings from a prospective population-based study. Ear Hear, 34(5), 535-552.

Chu, C., Choo, D., Dettman, S., Leigh, J., Traeger, G., Lettieri, S.,...Dowell, D. (2016, May). Early intervention and communication development in children using cochlear implants: the impact of service delivery practices and family factors. Podium presentation at the Audiology Australia National Conference, Melbourne, Australia.

Cupples, L., Ching, T.Y.C., Button, L., Leigh, G., Marnane, V., Whitfield, J.,...Martin, L (2018). Language and speech outcomes of children with hearing loss and additional disabilities: identifying the variables that influence performance at five years of age. International Journal of Audiology, 57(2), S93-S104.

Dettman, S., Dowell, R. Choo, D., Arnott, W., Abrahams, Y., Davis, A., . . . Briggs, R.J. (2016). Long-term communication outcomes for children receiving cochlear implants younger than 12 months: A multicenter study. Otology and Neurotology, 37(2), e82-95.

Dettman, S., Wall, E., Constantinescu, G., & Dowell, R. (2013). Communication outcomes for groups of children using cochlear implants enrolled in auditory-verbal therapy, aural-oral, and bilingual-bicultural early intervention programs. Otology and Neurotology, 34, 451-459.

Freeman, S.R., & Sennaroglu, L. (2018). Management of cochlear nerve aplasia. Advances in Hearing Rehabilitation, 81, 81-92.

Gallaudet Research Institute. (2011). Regional and national summary report of data from 2009-10 annual survey of deaf and heard of hearing children and youth. Washington, DC: GRI, Gallaudet University. Retrieved from https://research.gallaudet.edu 

Geers, A.E., Mitchell, C.M., Warner-Czyz, A., Wang, N., Eisenberg, L., & CDaCI Investigative Team. (2017). Early sign language exposure and cochlear implantation benefits. Pediatrics, 40(1), e20163489.

Hang, A.X., Roush, P.A., Teagle, H.F., Zdanski, C., Pillsbury, H.C., Adunka, O.F., & Buchman, C.A. (2015). Is "no response" on diagnostic auditory brainstem response testing an indication for cochlear implantation in children? Ear and Hearing, 36(1), 8-13.

Jerger, J., & Hayes, D. (1976). The cross-check principle in pediatric audiometry. Archives of Otolaryngology, 102(10), 614-620.

Leigh, J.R., Dettman, S.J., & Dowell, R.C. (2016). Evidence-based guidelines for recommending cochlear implantation for young children: audiological criteria and optimizing age at implantation. International Journal of Audiology, 55, S9-S18.  

Markman, T.M., Quittner, A.L., Eisenberg, L.S., Tobey, E.A., Thal, D., Niparko, J.K.,...CDaCI Investigative Team. (2011). Language development after cochlear implantation: an epigenetic model. Journal of Neurodevelopmental Disorders, 3, 388-404.  

Mitchell, R., & Karchmer, M. (2004). Chasing the mythical ten percent: parental hearing status of deaf and hard of hearing students in the United States. Sign Language Studies, 4(2), 138-163.     

Papsin, B. (2005). Cochlear implantation in children with anomalous cochleovestibular anatomy. The Laryngoscope, 115(Suppl. 1), S1-S26.

Picard, M. (2004). Children with permanent hearing loss and associated disabilities: revisiting current epidemiological data and causes of deafness. Volta Review, 104. 221-236.    

Wu, C., Lee, L., Chen, C., Chan, K., Tsou, Y., & Ng, S. (2015). Impact of cochlear nerve deficiency determined using 3-dimensional magnetic resonance imaging on hearing outcome in children with cochlear implants. Otology & Neurotology, 36, 14-21.