March 13, 1998
The Second Workshop of the NIDCD Working Group on Early Identification of Hearing Impairment was held on March 13, 1998, in Rockville, Maryland. The purpose of the workshop was to identify some of the research opportunities offered by neonatal hearing screening programs, specifically in the diagnostic strategies for characterizing the hearing impairment and in the intervention strategies for remediating hearing impairment. The workshop was designed to provide advice to the NIDCD for identifying research to be supported through the federal government grant and contract processes. Representatives from the Centers for Disease Control and Prevention and the Maternal and Child Health Bureau, NIDCD's federal agency partners supporting the early identification of hearing impairment, and members of the Working Group were present. Amy Donahue, Ph.D., and Lynn Luethke, Ph.D., Division of Human Communication, NIDCD, cochaired the workshop, which was supported by a grant from the Robert Wood Johnson Foundation.
The workshop convened at 8:00 a.m. A welcome was provided by James Battey, Jr., M.D., Ph.D., Director, NIDCD. Dr. Donahue then provided the charge to the workshop. She reminded the Working Group that the process of screening was the focus of the first workshop of the Working Group and that while much remains to be done in that area, the field is awaiting the results from currently supported studies on screening. The focus of the second workshop was on the issues following neonatal hearing screening, specifically the diagnostic and intervention strategies. Two issues were highlighted for the Working Group to consider in their deliberations. First, the discussions were to focus on the diagnostic and intervention processes immediately after an infant is identified as having a potential hearing problem. Although these issues are also critically important for the older pediatric population, the workshop was to focus on very young infants and the period following neonatal screening. Second, the degree of hearing impairment on which the Working Group was to focus should be consistent with the degrees of hearing impairment being identified in neonatal hearing screening programs. Current studies indicate that approximately 10%-20% of the babies identified through neonatal hearing screening have profound hearing impairment. The other 80%-90% of the identified babies have lesser degrees of hearing impairment. This represents a population of infants on which there are very few data. Thus, there is an urgent need to be able to characterize auditory function and to determine which intervention strategies will optimize development for the entire spectrum of infants with hearing impairment.
A brief presentation was made by Nigel Paneth, M.D., on issues to be considered in a screening program. Each member of the Working Group then spoke briefly about what they believed to be the most pressing research questions in diagnostic and intervention strategies following neonatal hearing screening. There was considerable overlap and agreement among the members of the Working Group on the most urgent issues, needs, and opportunities. The Working Group, under the direction of Drs. Donahue and Huerta, subsequently formulated recommendations to the NIDCD regarding the most pressing research questions in diagnostic and intervention strategies that follow neonatal hearing screening. The workshop was adjourned at 2:00 p.m.
Following are the research recommendations resulting from the second workshop of the NIDCD Working Group on Early Identification of Hearing Impairment. These recommendations are categorized into four areas:
- Characterization of Auditory Performance,
- Amplification and Sensory Aids,
- Intervention Strategies, and
- Overarching Strategies.
Characterization of Auditory Performance
The ability to characterize auditory performance is limited in infants, especially in infants younger than 6 months of age. The determination of appropriate intervention strategies is, however, critically dependent upon the ability to characterize auditory performance. The development of new age-appropriate measurement tools and/or the refinement of existing tools is needed. The measurement tools should allow for the determination of the type (site of lesion), degree (mild to profound), and configuration (frequency specific information) of the auditory deficit for each ear. Current technologies that provide frequency specific information (frequency specific auditory brainstem response) need refinement for increased efficiency. Better physiologic and behavioral measures to predict frequency specific thresholds, as well as measures allowing for the determination of middle ear status and function, are needed especially for infants under six months of age. These include observer based psychophysical approaches, as well as refinement of existing algorithms for use in operant conditioning paradigms. Additional needs are to understand the development of speech perception in normal and hearing impaired infants, along with addressing the myriad of factors that may impact this development, such as sensory-neural dynamics, central auditory perceptual processes, and linguistic-cognitive processes. Methods for characterizing suprathreshold auditory function and for examining speech and language acquisition using vocalizations and other communication modes are needed.
The etiology and occurrence of fluctuating and antenatal hearing impairment remains poorly understood and poorly documented in neonates and infants. Some examples include the roles of middle ear fluid and otitis media in fluctuating hearing impairment, and the role and interaction of maturation effects in late onset hearing impairment. Infants identified with apparently normal outer hair cell cochlear function but abnormal auditory nerve/brainstem responses (i.e. auditory neuropathy) require objective measures to further define this type of auditory impairment. Finally, the occurrence of progressive, later onset and fluctuating hearing impairment, as well as the current availability of simple and efficient hearing screening technology, suggests that models need to be developed to identify infants at risk for hearing impairment after the newborn period (e.g. monitoring hearing at pediatric well-baby visits).
Universal newborn hearing screening is gaining momentum throughout the nation. Many states are voluntarily screening all live births or passing legislation in this area. It is expected that in the near future approximately 19 states will screen all newborns for hearing impairment before discharge from the hospital. This number is expected to increase rapidly in the next decade. As more newborns are screened for hearing loss, there will be a large increase in the number of infants referred for diagnostic and intervention services. However, there are many parts of the country where pediatric audiological services are not readily available. Indeed there can be a considerable time delay between the referral from screening to the diagnosis of hearing impairment. Research is needed to support the development of a standardized protocol for the characterization of auditory function in infants.
Amplification and Sensory Aids
Hearing aids are commonly used as intervention measures for sensorineural hearing impairment and are, in most instances, fitted only after the hearing impairment is well-characterized. Currently, the selection and fitting of hearing aids on infants and young children remains an imprecise process and research is urgently needed to determine appropriate hearing aid selection and fitting strategies for infants. The comparison of available prescriptive methods and strategies, the development of new prescriptive strategies for various degrees of hearing impairment, the use of probe microphones, the determination of the appropriate type of hearing aid technology (e.g., analog, digital, compression, programmable) and their interaction with age, degree of hearing impairment, and numerous other variables, all deserve study. The comparative benefits of other types of amplification hardware, such as assistive listening devices, cochlear implants, and vibrotactile devices, used in isolation or combination, require further research for various degrees of hearing impairment. Overamplification and its potential long-term effects also require further study.
Existing methods and outcome measures do not allow differentiation among various prescriptive hearing aid selection and fitting strategies. Thus, there is an urgent need to develop appropriate and sensitive outcome measures of fitting strategies for infants and young children. These measures must allow for the effects of age and maturation, the type of technology and signal processing strategy in use, and the type, degree, configuration, and etiology of hearing impairment to be apparent. Both threshold and suprathreshold measures are needed for infant hearing aid selection and fitting.
Some of the weakest links in hearing aid fitting and use in young infants are practical issues, such as ergonomics. Such factors relate to hearing aid utilization (e.g., keeping a hearing aid on an infant) and to changes in the shape of the ear canal and pinna naturally occurring with maturation, which affect the proper fit of the earmold and the associated risk of acoustic feedback. These practical issues are also appropriate for research and development efforts.
Intervention and Follow-Up
Following the diagnosis of hearing impairment, intervention strategies are initiated to mitigate the effects of hearing impairment on the communicative, educational, and social development of the child. There have been very few well-controlled studies of the efficacy of intervention strategies. The few published studies focus predominantly on individuals who are deaf or who have profound hearing impairment. However, since the majority of children with hearing impairment identified by neonatal hearing screening have lesser degrees of hearing impairment, there is now a population of children being referred for intervention on which data are virtually nonexistent. There is a critical need for the development of intervention models based on a "best fit" between the intervention and a constellation of subject and environmental factors, such as degree of hearing impairment, age of diagnosis and intervention, family environment, socioeconomic status, intervention type
There is a lack of appropriate outcome measures to be used in determining the efficacy of intervention programs for individuals with hearing impairment. This is especially true in infants in the birth to six-month period, and of measures which include family issues and parent-child interactions. Clearly, such means of assessing outcome need to be developed and standardized. These include both baseline measures (benchmarks of development that constitute "appropriate" development) as well as age-specific and function-specific tools for children with hearing impairment. Baseline measures needed include auditory skill development, maturation of both the peripheral and central nervous system, suprathreshold perception, vocal production, gestural and other communication, specific aspects of language learning (including morphology and syntax), and caregiver and parent-child interactions (sensory and motor). The development of a database of prelinguistic vocalization samples from both normal hearing and hearing impaired infants, especially in the first 18 months of life, which could be used to form benchmarks for determining initial status as well as for monitoring progress, would be a valuable tool for research in this area.
Outcome efficacy is a critical area of research need. Because of the extreme heterogeneity of the population and the relatively low incidence of hearing impairment, these studies will need to be multi-center and longitudinal. Efficacy studies should include not only child focused outcomes, but should also include interactions among variables beyond the child, such as family dynamics and parent-child interactions. Such studies would appropriately define outcome expectations for the clinician and the families of the infants with hearing impairment.
OVERARCHING ISSUES: Screening Program Benefit, Sensitive Periods, Etiology and Medical Management, and Translational Research
Screening Program Benefit
The relationship between neonatal hearing screening programs and overall benefit to children with hearing impairment, their families, and society at large has not yet been defined. There is no universally agreed upon target or criterion threshold for the determination of whether an infant passes a hearing screening test or is referred for re-screening or diagnostic evaluation. As the target threshold is lowered and made more stringent, the number of false positives referred for further testing increases. Research to define the long-term benefit of early identification and intervention for various degrees of hearing impairment is needed. Research is required that delineates how to maximize the potential benefits of hearing screening programs and how to minimize parental anxiety and promote a healthy, robust parent-infant bond.
Although there is persuasive evidence for a very early and well-defined "critical period" or "sensitive period" for auditory and vocal learning in birds and other animal models, such studies are not feasible in humans for ethical reasons. However, there is clear evidence that normal human infants begin the speech and language acquisition process early in the neonatal period. Furthermore, perturbations in that normal process produce lasting effects. Thus, while an exact "sensitive period" for the effects of hearing impairment on speech and language development is not known for humans, the existing evidence supports the notion that it is confined to a period early in life (the current estimate is that it is within the first six months of life). Determination of the "sensitive periods" for auditory, speech, language, cognitive, social, emotional, and motor development, as well as other related sensory interactions (e.g., vision and language), would provide a clear rationale and guidance for the most appropriate timing of intervention for hearing impairment.
Another area in need of study, a reciprocal consideration to "sensitive" periods, is the long-term effects of intervention strategies and rehabilitative devices (e.g., hearing aids, cochlear implants, assistive listening systems, tactile devices, combinations of these). For example, neither the short- nor long-term effects of various rehabilitation devices or intervention strategies on auditory function are known. All issues related to sensitive periods (e.g. plasticity, short-and long-term sensory deprivation) are relevant. Further research is required to shed light on these important and critical issues.
Etiology and Medical Management
The determination of etiology and the integration of medical diagnosis into the ongoing management programs of infants should occur early in the process of the identification of hearing impairment. Early identification of hearing impairment requires that research be directed at understanding the pathophysiology of the hearing impairment at birth. New tools and techniques, such as molecular biology, molecular genetics, and imaging, should be aimed at determining the etiology of hearing impairment. New diagnostic tools and targeted therapies for viral, autoimmune, and genetic hearing impairment should have a great impact on the treatment and prevention of many forms of hearing impairment (e.g., fluctuating and progressive hearing impairment, cytomegalovirus, and otitis media). Molecular diagnostics and molecular genetics are advancing rapidly and should be integrated rapidly into medical programs for prevention and treatment of early identified hearing impairment. New models of responsive multidisciplinary medical management are needed.
Means to achieve the rapid integration of new techniques and laboratory-research findings into clinical or habilitative/rehabilitative programs remains a high priority for all research needs as outlined in this document. Translational research will facilitate the rapid and efficient integration of research findings into clinical practice.