Early Hearing and Communication Development

Chapter VI: Hearing and Communication Development

Amplification

Author: Dr. Richard Seewald

There is evidence that properly fitted hearing aids can improve auditory performance in children with hearing impairment.^1-3 Therefore, the early use of binaural amplification in infants with measurable residual hearing bilaterally is likely to be beneficial. To take full advantage of the early diagnosis of hearing impairment, the accurate fitting of hearing aid amplification must be undertaken in a timely manner, optimally within one month of the confirmation of hearing impairment and, whenever possible, no later than 6 months of age.⁴ The fitting of amplification should proceed when: (1) hearing impairment has been confirmed; (2) hearing aid fitting has been chosen by the family following a review of expectations and options that has been presented in a complete and objective manner; and (3) when there is an absence of specific contraindications following a medical evaluation preferably performed by an otolaryngologist with extensive pediatric experience. Lastly, to ensure the accurate fitting of amplification with young infants, highly qualified professionals and pediatric-specific hearing instrument fitting protocols are required.^5,6

Key Elements in Fitting Amplification in Young Infants

Assessment for Hearing Instrument Fitting

The accurate fitting of amplification in infants is dependent on the results of a valid and comprehensive assessment. Assessment data that are required before proceeding with the fitting of amplification include:

• frequency-specific and ear-specific estimates of hearing sensitivity
• determination of the type of the impairment - i.e., conductive, sensory, mixed (conductive and sensory), auditory neuropathy (AN)
• medical clearance for hearing instrument fitting
• measurement of the infant's occluded external ear acoustics using the real-ear to coupler difference (RECD) procedure⁷

Frequency-specific air conduction (AC) and, when indicated, bone-conduction (BC) threshold estimates must be obtained before proceeding with the prescription and fitting of amplification for young infants. For newborns and infants under the developmental age of 6 months, frequency- and ear-specific estimates of hearing sensitivity can be obtained by auditory brainstem response (ABR) measures.⁸ Frequency-specific ABR data are necessary for accurate estimation of the degree and configuration of the hearing impairment in each ear. A click ABR measure alone is not sufficient for the accurate fitting of amplification. For older infants, ear-specific behavioural threshold measures should be obtained using visual reinforcement audiometry (VRA). Acoustic immittance measures, including high-frequency tympanometry and middle ear reflex testing, and otoacoustic emission (OAE) are required to determine the type of hearing impairment present.⁶

The acoustic properties of the external ears of infants show high between-subject variability.^9-11 For accurate hearing instrument selection and fitting, this variable needs to be accounted for and applied at several stages in the amplification selection and fitting process. The RECD measure provides a reliable and valid means by which to capture the individual external ear acoustics for the purposes of fitting amplification.^7,12,13 Thus, in addition to conventional diagnostic audiometric test procedures, the prescription and fitting of amplification should not proceed until the infant's RECD has been quantified. This information is applied to the threshold assessment data to individualize the estimated hearing level to sound pressure level (SPL) transform used by modern pediatric hearing instrument prescription procedures.¹⁴ In addition, this information is used at a later stage in the amplification fitting process to define 2cc coupler electroacoustic performance characteristics for the individual infant, as well as to predict real-ear hearing instrument performance from coupler-based electroacoustic measures.¹³

Hearing Aid Selection

A systematic, evidence-based prescriptive method specifically developed for pediatric applications should be applied in the fitting of amplification in young infants.^5,6 The prescriptive method should: (1) provide target values for the required frequency/ gain function for a range of input levels; (2) provide target performance values by frequency for the maximum hearing instrument output; (3) systematically account for the developmental variations and changes over time in external ear acoustics; and (4) ensure audibility for a wide range of speech input levels and frequencies.^5,6

Given the rapid advancement and ongoing introduction of new hearing instrument technology, further research is needed to determine the benefits and/or limitations of new digital signal processing options for application with infants.⁶

Electroacoustic Verification

The purpose of the electroacoustic verification stage of the hearing instrument fitting process is to ensure that the measured performance of the instrument to be fitted meets the prescribed criteria for each infant. Comprehensive electroacoustic verification for hearing instruments to be fitted to young infants requires that:

• measurements be made with speech or simulated speech test signals to accurately predict the hearing instrument gain in use environments
• measurements be made at multiple input levels to predict audibility for a range of everyday speech input conditions
• measurements of hearing instrument maximum output be obtained using pure tone test signals^6,15

At present, the evidence suggests that a "simulated real-ear" approach to electroacoustic verification be applied in fitting amplification with the infant population. This includes the verification of all electroacoustic parameters in a 2cc coupler within a hearing instrument test chamber. Subsequently, an individualized acoustic transform, that includes the infant's RECD, is applied to predict real-ear hearing instrument performance.⁷ A study by Seewald and colleagues¹³ confirmed that this approach can be used to derive accurate predictions of real-ear aided gain (REAG) and the real-ear saturation response (RESR) in children. One advantage of this "simulated real-ear" approach to verification is that it does not introduce measurement error that can occur with conventional sound field probe-microphone measurements.

Monitoring Performance with Amplification

Once an infant has been properly fitted with hearing aids, the infant's performance with amplification must be closely monitored and evaluated. Over time, consideration is given to candidacy for additional assistive hearing technologies (e.g., FM systems) and/or alternative devices (e.g., cochlear implants).*

Frequent reassessment is important to ensure appropriate amplification parameters and hearing aid benefit over time. While there is a lack of research involving the validation of amplification in infants, there is a possibility that this may change as infant hearing screening programs progress.^10,16

Studies have revealed contradictory findings that hearing aid use can cause marked threshold shifts on a child's aided ear. Poorly controlled aspects of retrospective studies and the use of group data contribute to these discrepancies. Therefore, frequent monitoring of thresholds and hearing aid functionality as part of a specific follow-up program for infants fitted with hearing aids is recommended.⁵

Notes

*Note: Cochlear implants have not been addressed within this section because this report deals predominantly with the infant in the first six months of life.

Conclusions

• Hearing aids can improve auditory performance in children with auditory impairment who have some hearing bilaterally.
• Coupler-based verification in conjunction with individual real-ear coupler difference (RECD) measurement is a valid procedure for the electroacoustic verification of hearing instruments.
• Further research is needed to explore new signal processing options.

Key References

1. Christensen LA. A comparison of three hearing-aid sound-processing strategies in a multiple-memory hearing aid for adolescents. Semin Hear. 1999;20(3):183-95.
2. Jenstad LM, Seewald RC, Cornelisse LE, Shantz J. Comparison of linear gain and wide dynamic range compression hearing aid circuits: Aided speech perception measures. Ear Hearing. 1999;20(2):117-26.
3. Jenstad LM, Pumford J, Seewald RC, Cornelisse LE. Comparison of linear gain and wide dynamic range compression hearing aid circuits II: Aided loudness measures. Ear Hearing. 2000;21(1):32-44.
4. Joint Committee on Infant Hearing. Year 2000 Position Statement: Principles and Guidelines for Early Hearing Detection and Intervention Programs. Am J Audiol. 2000;9:9-29.
5. The Pediatric Working Group of the Conference on Amplification for Children with Auditory Deficits. Amplification for infants and children with hearing impairment. Am J Audiol. 1996;5(1):53-68.
6. American Academy of Audiology [homepage on the Internet]. Pediatric amplification protocol. 2003. Available from: <http://www.audiology.org>.
7. Moodie KS, Seewald RC, Sinclair ST. Procedure for predicting realear hearing aid performance in young children. Am J Audiol. 1994;3:23-31.
8. Stapells DR. Frequency-specific evoked potential audiometry in infants. In: Seewald RC, editor. A Sound Foundation Through Early Amplification. Stafa, Switzerland: Phonak AG; 2000. p. 13-31.
9. Feigin JA, Kopun JG, Stelmachowicz PG, Gorga MP. Probe-tube microphone measures of ear canal sound pressure levels in infants and children. Ear Hearing. 1989;10(4):254-8.
10. Westwood GF, Bamford JM. Probe-tube microphone measures with very young infants: Real ear to coupler differences and longitudinal changes in real ear unaided response. Ear Hearing. 1995;16(3):263-73.
11. Bagatto MP, Scollie SD, Seewald RC, et al. Real-ear-to-coupler difference predictions as a function of age for two coupling procedures. J Am Acad Audiol. 2002;13(8):407-15.
12. Sinclair ST, Beauchaine KL, Moodie KS, et al. Repeatability of a real-ear-tocoupler difference measurement as a function of age. Am J Audiol. 1996;5:52-6.
13. Seewald RC, Moodie KS, Sinclair ST, Scollie SD. Predictive validity of a procedure for pediatric hearing aid fitting. Am J Audiol. 1999;8:143-52.
14. Scollie SD, Seewald RC, Cornelisse LE, Jenstad L. Validity and repeatability of level-independent HL-to-SPL transforms. Ear Hearing. 1998;19:407-13.
15. Scollie SD, Seewald RC. Electroacoustic verification measures with modern hearing instrument technologies. In: Seewald RC, Gravel JS, editors. A Sound Foundation Through Early Amplification 2001. Stafa, Switzerland: Phonak AG; 2002. p. 121-37.
16. Stelmachowicz PG. Hearing aid outcome measures for children. J Am Acad Audiol. 1999;10(1):14-25.

Communication Development

Author: Dr. Andrée Durieux-Smith

The majority of children with a permanent childhood hearing impairment (PCHI) are born to parents who have normal hearing and limited knowledge of hearing impairment. After a diagnosis of PCHI has been confirmed, parents need to choose an appropriate hearing and communication development (HCD) strategy. Some may choose amplification and a communication development option emphasizing the development of spoken language while others may choose not to amplify their child and pursue a manual mode of communication.

Historically there have been two major philosophies aimed at developing communication skills: oralism and manualism. The goal of oralism is the development of spoken language skills. Several variants have been developed. These include the aural-oral (A-O) approach which advocates the use of hearing through the use of amplification devices, which in turn is facilitated by speech reading. The highly structured auditory verbal therapy (AVT), which is another form of the oral approach, relies almost exclusively on residual hearing and the development of listening skills.

The manualists, on the other hand, do not feel that it is necessary for individuals with a permanent hearing impairment to develop spoken language and see signing or visual language systems as a natural language of the deaf. This communication approach is seen as facilitating the full participation in the deaf culture. Many sign language systems (such as American Sign Language (ASL) and Langue des signes quebecois (LSQ)) are visual languages with their own grammar and syntax. For this approach to be effective, the child must be in contact with adults who are fluent in the chosen sign language system.

The total communication (TC) approach, which until recently was a popular option, combines elements of the oral and manual approaches. Various methods of communication, including sign language, finger spelling, natural gestures, speech reading and spoken language, were all integrated. The simultaneous use of spoken and signed language was seen as a way to facilitate the development of communication skills.¹ TC was a multisensory approach where amplification and signing were used together. Proponents of this approach believed that signing would facilitate the development of spoken language.

Regardless of the approach, the belief is that early intervention is key to the development of communication and social skills and of academic functioning. Early intervention is being facilitated by the development of universal newborn hearing screening (UNHS) programs. In addition, technological developments such as cochlear implants are providing increased access to auditory information by children with a PCHI.

In order to select an appropriate HCD approach for their child, parents need to be provided with adequate information. The choice of an HCD option for parents must be an informed choice based on scientific evidence. In order to determine the effectiveness of the four main types of approaches used until recently (A-O, AVT, ASL, TC) for children with a congenital PCHI, a systematic review of the empirical evidence was carried out by the Chalmers Research Group in Ottawa.² This section provides a brief summary of the results of the systematic review.

The search strategy consisted of a variety of existing electronic databases. Studies were eligible for inclusion if they were characterized by any level of evidence above opinion, if they involved children with a congenital PCHI, and if at least one subject in the study had received one of the four HCD options of interest to the review. Several independent reviewers were involved in the selection of the studies.

Two types of studies were found to be relevant. These included direct and indirect evaluations of the impact of the approaches of interest to the review. In direct studies, a variety of designs were identified (uncontrolled case study to randomized controlled trials (RCTs)) and these included any or no comparators, and were conducted specifically to determine the effectiveness of one of the approaches of interest. Indirect studies established the potential utility of at least one of these types of programs.

Of the two types of studies, direct and indirect, the direct types of evaluation were more likely to have instituted scientific methods of control to assure the study's internal validity. Indirect studies had a different focus and were somewhat less rigorous. Of 625 citations, 194 unique studies were entered into data abstraction. This included 91 direct and 103 indirect evaluations of review-relevant programs. Evidence tables were derived with variables highlighted by clinical content experts. An examination of these tables indicates a preponderance of missing data - examples of missing data included sample size, degree of hearing impairment, route to identification and types of amplification.

The observations obtained in the systematic review do not permit the confirmation or disconfirmation of the absolute or comparative effectiveness of any of the four HCD options reviewed. One of the major reasons, as previously stated, was the preponderance of missing data in the majority of studies. This was attributed to the failure of investigators to recognize the importance of investigating the collected data according to key population- and intervention-based variables, the inability to reliably measure the variables or to a failure to report the data.

The systematic review indicates that it was impossible to ascertain the exact number and other characteristics of children meeting the review's eligibility criteria. This gave rise to an incomplete qualitative synthesis. The authors of the systematic review conclude that the state of the research literature on HCD approaches appears to be one of disarray with considerable amounts of missing and divergent information. The question concerning the effectiveness of the four review-relevant approaches for children with a congenital PCHI cannot at the moment be answered in the affirmative or the negative. The authors acknowledge that the questions concerning the effectiveness of habilitation programs are complex as a multitude of variables can have an impact on outcome.

A key goal of future research could be the ascertainment of the approach that would be most appropriate for each child and his or her family. HCD options need to be scientifically based while taking into account social and cultural factors. Well-designed and controlled studies are needed, as parents require the scientific evidence that will allow them to make informed choices on the most appropriate HCD option for their child.

Conclusions

• A systematic review of the research on outcomes of the most common communication development options (aural-oral (A-O), auditory verbal therapy (AVT), American Sign Language (ASL) and total communication (TC)) revealed that inter-study variability and limitations of study design and analysis preclude the establishment of the effectiveness of any of the four communication development options.
• The lack of definitive proof, however, does not mean these communication development options are ineffective, but that further studies are required.
• Progress in this area would be facilitated by development of quantitative measures of oral and manual language development applicable to infants.

Key References

1. Lynas W. Communication options in the education of deaf communication. San Diego: Singular Publishing Group Inc.; 1994.
2. Schachter H, Clifford TJ, Fitzpatrick E, et al. Systematic Review of Interventions for Hearing Loss in Children. Submitted to Health Canada. November 2002.

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