preschool children suggest that the speech .... five test areas of the SIFTER (i.e., academics, attention ... SIFTER to evaluate the academic performance.
Minimal Hearing Loss in Children: Minimal But Not Inconsequential Anne Marie Tharpe, Ph.D.,1 Douglas P. Sladen, Ph.D.,2 Jeanne Dodd-Murphy, Ph.D.,3 and Stephen J. Boney, Ph.D.4
ABSTRACT
It has been 25 years since Bess published his first work on unilateral hearing loss in children. Those early articles triggered considerable interest in the audiology and medical communities and represented an expansion of our focus at that time on children with severe to profound degrees of hearing loss to include those with lesser degrees of hearing loss. Before Bess’ work, professionals were of the opinion that minimal degrees of hearing loss were of little consequence to a child’s development. However, these early studies demonstrated that children with minimal degrees of permanent hearing loss were, in fact, at considerable risk for academic and behavioral problems. Today those problems persist, and we are still wrestling with which children with minimal degrees of hearing loss require intervention, what type(s) of intervention is most effective, and whether preventive measures exist to avoid the commonly reported problems known to plague some of these children. This article reviews the early studies conducted by Bess and his colleagues documenting the psychoeducational, audiological, and behavioral difficulties experienced by children with permanent unilateral and minimal bilateral hearing loss. In addition, contemporary studies are reported along with a summary of current thinking on the appropriate management of these populations. KEYWORDS: Minimal hearing loss, unilateral hearing loss
Learning Objectives: As a result of this activity, the participant will be able to (1) list two to three hearing technology options for children with minimal degrees of hearing loss, and (2) cite two to three potential developmental risks for children with minimal degrees of hearing loss.
1 Department of Hearing and Speech Sciences, Vanderbilt University School of Medicine, Nashville, Tennessee; 2 Department of Communication Sciences and Disorders, The University of Texas at Austin, Texas; 3Department of Communication Sciences and Disorders, Baylor University, Waco, Texas; 4Education and Communication Disorders, University of Nebraska, Lincoln, Nebraska. Address for correspondence and reprint requests: Anne Marie Tharpe, Ph.D., Professor, Department of Hearing and Speech Sciences, Vanderbilt University School of
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Medicine, 1215 21st Ave. South, Medical Center East, S. Tower, #8310, Nashville, TN 37232 (e-mail: anne.m.tharpe @vanderbilt.edu). A Tribute to Fred H. Bess: 40 Years of Influence in Audiology; Guest Editor, Anne Marie Tharpe, Ph.D. Semin Hear 2009;30:80–93. Copyright # 2009 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662. DOI 10.1055/s-0029-1215437. ISSN 0734-0451.
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lthough the first Bess citation on unilateral hearing loss (UHL) in children appeared in 1980,1 a review of the literature reveals that his initial interests in minimal degrees of hearing loss may have stemmed from some of his earlier work in adults with high-frequency, noise-induced hearing loss, most notably, ‘‘Two Experiments on Subtle Mid-Frequency Hearing Loss and Its Influence on Word Discrimination in NoiseExposed Listeners.’’2 That early work, coupled with concerns heard from parents of children with UHL, launched what proved to be one of Bess’s richest veins of research. Despite a conservative prevalence estimation of 0.55 per 1000 infants with permanent UHL or mild bilateral hearing loss3 (MBHL), very little attention was given to this group of children prior to the release of Bess’s first studies. In fact, audiologists, educators, and physicians alike were likely to counsel families not to worry about their child’s UHL—that it would not result in any learning problems.4 Those early Bess studies changed our practice patterns and gave rise to numerous other investigations of minimal hearing loss in children, as well as public policy changes.5,6 The definition of permanent minimal hearing loss proffered by Bess and colleagues7 has been suggested for widespread use to allow for comparisons of findings across studies.8,9 Specifically, that definition includes: Unilateral sensorineural hearing loss: average
air-conduction thresholds (0.5, 1.0, 2.0 kHz) 20 dBHL in the impaired ear and an average air-bone gap no greater than 10 dB at 1.0, 2.0, and 4.0 kHz and average airconduction thresholds in the normal-hearing ear 15 dBHL; Bilateral sensorineural hearing loss: average pure-tone thresholds between 20 and 40 dBHL bilaterally with average air-bone gaps no greater than 10 dB at frequencies 1.0, 2.0, and 4.0 kHz; High-frequency sensorineural hearing loss: air-conduction thresholds > 25 dB HL at two or more frequencies above 2 kHz (i.e., 3.0, 4.0, 6.0, or 8.0 kHz) in one or both ears with air-bone gaps at 3.0 and 4.0 kHz no greater than 10 dB.
In addition to the term ‘‘minimal,’’ a variety of other terms are used to describe this degree of hearing loss including ‘‘subtle,’’ ‘‘slight,’’ and ‘‘mild.’’ However, considerable discussion has ensued about this terminology because despite the implication of these terms, Bess has reminded us that ‘‘minimal is not inconsequential.’’10 Using the term ‘‘minimal’’ to describe the hearing losses discussed here belies the fact that many children with these degrees of hearing loss exhibit more than minimal difficulties as a result. In this article, we provide a history of the work conducted on permanent minimal hearing loss in children that has informed our current thinking. Furthermore, we discuss the benefits and limitations of management strategies for children with minimal degrees of hearing loss and the work yet to be done.
PSYCHOEDUCATIONAL IMPACT OF PERMANENT UNILATERAL HEARING LOSS In a series of studies published by Bess and colleagues in the early 1980s, an attempt was made to characterize the psychoeducational status of children with UHL relative to their normal-hearing peers.11–15 This characterization began with an examination of 60 schoolage children with UHL resulting in the alarming revelation that approximately a third of these children failed at least one grade in school, and almost 50% either failed a grade or required resource assistance.16 Shortly after this report appeared, these findings were replicated in a study conducted in Arizona17 as well as numerous other studies abroad.18–20 At least a couple of studies did not find academic achievement differences between children with UHL and those with normal hearing.21,22 Having determined that many children with UHL were experiencing significant educational difficulties, a series of studies were planned to examine more closely the potential contributing factors, such as cognitive, auditory, or speech-language deficits. The audiological profile most closely associated with poor academic outcomes included children with right ear impairment13,17,19 and those with more severe degrees of UHL.12,23,24 And, despite
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the long-held belief that children with UHL would have little listening difficulty as long as the desired speech signal was directed toward their normal-hearing ear (monaural direct with speech directed toward the normal-hearing ear and noise directed to the poor ear), Bess and colleagues13 demonstrated that in quiet or in background noise, children with UHL had poorer speech perception scores than their normal-hearing peers regardless of the location of the speech signal source (i.e., monaural direct or monaural indirect). Furthermore, children with right ear UHL had significantly poorer speech perception scores than those with left UHL. Confirmatory findings have been reported from other laboratories. For example, Bovo et al18 found significantly poorer speech recognition performance for a group of children with UHL as compared with their normalhearing peers even in a monaural direct condition. Similarly, Ruscetta and colleagues25 examined performance of school-age children with severe-to-profound UHL on speech recognition tasks as compared with children with normal hearing. When evaluated in noise in a variety of speaker azimuth conditions, the children with UHL required greater signal-to-noise ratios (SNRs) than children with normal hearing. This difficulty with speech perception in noise was observed for nonsense syllable and sentential speech materials. Examination of speech and language abilities of children with UHL have not revealed any specific deficits.15,22,26,27 However, Klee and Davis-Dansky15 found that children with UHL who had failed a grade in school had significantly lower verbal IQ scores than children with UHL who were academically successful. Despite group differences, both the academically successful and unsuccessful UHL groups had verbal IQs within the normal range. Tieri and colleagues26 were also unable to identify any speech or language problems from case history reports obtained from parents of children with UHL. But most parents surveyed reported that their children had ‘‘learning problems.’’ Most studies of speech and language abilities of children with UHL have included school-age children. However, more recently, results on a small group of 15 children with
congenital UHL between 15 and 62 months of age have been reported.28 Of this group, 27% were found to have significant language delays on a battery of speech and language measures. These preliminary findings with a group of preschool children suggest that the speech and language difficulties experienced by children with UHL might improve by the time children reach school age or might not be sensitive to testing protocols used with the school-age population.
PERCEPTUAL CONSEQUENCES OF PERMANENT MINIMAL BILATERAL HEARING LOSS The acoustic environment in classrooms can have a significant effect on speech perception and learning in children that ultimately can affect academic achievement. Numerous studies over several decades have documented the poor acoustic conditions represented in classrooms.29–32 Furthermore, children, regardless of hearing status, require more favorable acoustic environments than adults to achieve equivalent speech recognition scores.33–39 In addition, children with hearing loss are adversely affected to a greater degree by poor listening conditions than their peers with normal hearing.40–43 The majority of studies that have examined the perceptual consequences of hearing loss in children have focused on the systematic effects of background noise and reverberation. Most of these studies have used groups of children with mild to moderately severe sensorineural hearing loss.42–45 One reason for this might be the use of a hearing loss classification system that considers auditory thresholds 25 dBHL to be within normal limits. Bess46 suggested that the use of a unitary average value to classify hearing loss might not be suitable to describe children with permanent MBHL. A pure-tone threshold range of –10 to 15 dBHL for defining normal auditory sensitivity has been suggested for use with children.47,48 A second reason may be that children with MBHL might not meet existing guidelines for provision of special education services. However, a few studies have examined the deleterious effects of classroom acoustic
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conditions on the perceptual abilities of children with mild or MBHL. Ross and Giolas49 administered monosyllabic word lists to a group of six school-age children with mild bilateral hearing loss (average pure tone sensitivity of 35 dBHL) and a control group with normal hearing. Lists were administered live voice in a classroom under three listening conditions: unaided, binaural aided, and binaural aided with a frequencymodulated (FM) receiver. Conditions 2 and 3 were administered only to the group with hearing loss. In the unaided condition, the minimally impaired group scored an average of 32% in comparison with 91% for the normal-hearing subjects. Aiding the minimally impaired subjects binaurally demonstrated limited improvement, and the use of an FM system improved speech recognition an average of 37%. In a replication study, Ross et al50 found similar results. One of the first studies to examine systematically the effects of noise and reverberation on a small group of children with MBHL was reported by Boney and Bess40 in 1984. They examined speech recognition of monosyllabic and sentential stimuli in a group of six children with permanent MBHL and normal hearing. Subjects with MBHL had pure tone thresholds between 15 and 30 dBHL for frequencies 0.5, 1, and 2 kHz, with thresholds no greater than 40 dBHL at 4 kHz. Speech recognition was examined in quiet, noise (þ6 SNR), reverberation (0.85 seconds), and noise and reverberation (þ6 SNR and 0.85 seconds). The noise and reverberation levels were chosen to simulate the acoustic characteristics of a general education classroom. The children with MBHL experienced greater difficulty listening to both types of stimuli in noise, reverberation, and noise and reverberation. Speech recognition performance, in general, was more adversely affected for monosyllabic words than for the sentential material. Additionally, a synergistic decrement in speech recognition was observed for the MBHL group when noise and reverberation were added. These results were consistent with those reported by Finitzo-Hieber and Tillman42 for children with mild to moderate sensorineural hearing loss.
In 1993, Crandell41 extended the work of Boney and Bess40 to include a larger subject pool and increase the number of SNR conditions. Specifically, 20 children with permanent MBHL and 20 children with normal hearing served as subjects. Children in the MBHL group had pure tone average thresholds (0.5, 1, and 2 kHz) between 15 and 30 dBHL in at least one ear, with thresholds 45 dBHL at 0.25 and 4 kHz. Both groups were evaluated in quiet and at SNRs of þ6, þ3, 0, 3, and –6 dB. The noise levels were chosen to represent SNRs found commonly in classroom environments. A recorded list of the Bamford-KowellBench sentences51 was played to each subject monaurally at each of the five SNRs. The subjects with MBHL performed more poorly than the normal-hearing group under most listening conditions. Furthermore, the difference in speech recognition performance between the two groups increased as the listening situation became less favorable. Johnson et al52 examined consonant and vowel recognition in a group of 12 children with minimal high-frequency hearing loss, 12 children with normal hearing, and 12 young adults with normal hearing. The children with minimal high-frequency hearing loss had hearing thresholds 20 dBHL between 0.25 and 1 kHz, with at least one threshold 30 dBHL at 2 to 8 kHz. The authors recorded nonsense syllables53 through a Knowles Electronics Mannequin for Acoustic Research (KEMAR) in a classroom (RT ¼ 0.7 seconds in quiet and with a background noise of þ13 dB). Each group listened to the tapes monaurally under earphones both in the quiet and noise conditions. Responses were analyzed for correct vowel and consonant identification. Overall, the normal-hearing adults achieved significantly higher identification for consonants and vowels both in quiet and in noise than the normal-hearing children and children with hearing loss. For consonant identification in quiet, the normal-hearing group scored significantly higher than the minimal high-frequency group. There was no significant difference among groups for consonant identification in noise. Vowel identification was not significantly different for either group of children in quiet or noise. In fact, mean differences were
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quite small for both conditions; 1%. Recall that Crandell41 reported that as SNR decreased, the difference in performance between normal listeners and those with MBHL increased. In this study, both groups had similar vowel and consonant recognition scores in noise. The disparity between these two studies is likely the result of the use of different stimuli and listening conditions. The effect of speaker-to-listener distance on speech recognition has received limited attention in children with hearing loss. Crandell and Bess54,55 examined the effect of speaker-tolistener distance on the speech recognition of monosyllabic words in normal-hearing children. Recordings were made through a KEMAR under conditions simulating a typical classroom (þ6 SNR; RT ¼ 0.45 seconds) at three speakerto-listener distances: 6, 12, and 24 feet. As expected, speech recognition decreased as speaker-to-listener distance increased, from an average of 89% at 6 feet to 36% at 24 feet. These results suggest that seating normal-hearing children farther away from the teacher may have a deleterious effect on speech recognition. It would be expected that children with MBHL might be at an even greater risk when seated farther away from the teacher than children with normal hearing. Crandell et al56 reported that providing instruction in small groups facilitated speech recognition. Collectively, these studies provide perceptual evidence that children with MBHL experience greater difficulty understanding speech than their normal-hearing peers under acoustic conditions that simulate those typically found in school classrooms. The explanation for this difficulty is not completely known. However, there likely are possible underlying cochlear changes that affect the temporal and spectral processing of speech for children with MBHL. This area deserves further investigation with the use of various psychoacoustic tasks.
EDUCATIONAL AND PSYCHOSOCIAL OUTCOMES OF CHILDREN WITH PERMANENT MBHL Recognizing the likelihood that speech perception difficulties could lead to more distal devel-
opmental effects, Bess and coworkers7 examined the prevalence of minimal hearing loss in school-age children and the academic performance and functional health status of these children relative to a group of matched peers with normal hearing. They found that 66 of 1218 children(5.4%) examined in grades 3, 6, and 9 demonstrated either sensorineural UHL (3%) or MBHL (2.4%). These children were then compared with a control group on standardized achievement test scores, teacher ratings on the Screening Instrument for Targeting Educational Risk57 (SIFTER), grade retention rate, and self-ratings on a functional health status questionnaire. Although the case group included participants with various permanent minimal hearing loss configurations (including UHL) and the sample size did not permit between-group analyses based on hearing loss category, results for the children with MBHL tended to reflect the results for the entire minimal hearing loss group. In the Bess et al study,7 student records were reviewed to obtain scores on the Comprehensive Test of Basic Skills, 4th edition58 (CTBS/4) and to establish rates of grade retention. Third graders with minimal losses showed significantly lower mean CTBS/4 scores on 7 of 12 subtests when compared to a group of children with normal hearing who were matched for grade, school, gender, and race. Sixth and ninth graders with minimal losses had mean CTBS/4 scores that were not significantly different from those of their counterparts with normal hearing. Thirty-seven percent of the minimal hearing loss group (grades 3, 6, and 9 combined) had repeated at least one grade in school. The percentage of children who had repeated one or more grades increased as grade level increased, ranging from 29.2% of the third graders with minimal loss to almost half (47.4%) of the ninth graders. The results from the CTBS/4 scores supported previous findings from a small sample of children with mild bilateral hearing loss.59 In that study, third and fourth graders with mild hearing loss scored significantly lower across numerous subtests of a school achievement test than did the matched control group with normal hearing. The deficit in performance was more pronounced in the third and fourth
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graders with mild hearing loss than for the first and second graders. Therefore, the authors proposed that the effects of mild hearing loss on basic academic abilities might increase with increasing grade. More recently, several studies across the United States have found similar academic difficulties in children with MBHL and UHL, suggesting that enhanced understanding of the difficulties experienced by these children has not resulted, as yet, in improved outcomes.28,60–62 Bess and his colleagues7 also administered the SIFTER to teachers of the children with minimal loss and the control group as another indicator of academic progress. Teachers were unaware of the hearing status of the children for whom the SIFTER was completed. A larger percentage of the children with minimal hearing loss (all three grades combined) were placed by their teachers in either the ‘‘marginal’’ or ‘‘failure’’ category of the SIFTER than were their peers with normal hearing. Furthermore, a higher proportion of the minimal hearing loss group was rated as having difficulty across the five test areas of the SIFTER (i.e., academics, attention, communication, class participation, and school behavior) than the control group; however, the difference reached statistical significance only for the communication area. More than a third of the children with minimal hearing loss showed failure scores in the areas of academics, attention, and communication, and thus were considered dysfunctional in these domains. Several other studies have used the SIFTER to evaluate the academic performance of children with MBHL.63–65 These studies have produced results similar to the Bess findings, suggesting that teachers observe higher levels of dysfunction in classroom settings for children with MBHL than their normalhearing peers. Most63 proposed that these differences might be exacerbated because children with MBHL and UHL are identified later and receive fewer support services than children with greater degrees of hearing loss. Historically, there has been little documentation of social or emotional difficulties in children with MBHL, especially from the child’s point of view. Research that included self-ratings of socio-emotional function in
children with MBHL evidenced dysfunction in areas such as self-concept and peer relations (social status in a regular classroom) but had very small sample sizes.66–68 Bess et al7 used the Cooperative Information Adolescent Chart Method69 (COOP) to assess functional health status for all participants in the sixth and ninth grades. This measure was designed to provide information about self-perception of emotional and physical health, particularly related to school and family environments. Children rated themselves on a 5-point scale (with 5 indicating the highest level of dysfunction) on 10 dimensions: stress, social support, selfesteem, emotional condition, family, schoolwork, behavior, energy, getting along with others, and overall health. When sixth- and ninth-grade data were combined, the mean ratings for the minimal hearing loss group were higher than those for the control group with normal hearing on all dimensions except ‘‘getting along with others.’’ Significant differences between groups were found in the areas of stress, self-esteem, and behavior.70 When the sixth and ninth graders were considered separately, the younger children with MSHL showed significantly higher mean ratings on the energy dimension, and the ninth-grade minimal hearing loss group demonstrated significantly higher mean scores on dimensions of stress and behavior.7 Approximately 25–30% of the sixth graders with minimal hearing loss reported a high level of dysfunction (a rating of 4 or 5) on the COOP dimensions of selfesteem and energy, a significantly higher proportion than for the normal-hearing group. A similar proportion of the ninth-grade minimal hearing loss group rated themselves as highly dysfunctional in the domains of social support and self-esteem (significantly higher percentages compared with the control group), whereas almost 60% of the ninth graders with minimal hearing loss classified themselves as highly dysfunctional in the stress domain. Other investigations of overall functional health status and quality of life of children with mild hearing loss or MBHL and/or their families have been reported.71–73 For example, Davis and coworkers71 surveyed 150 families of children with MBHL or UHL regarding their quality of life. Approximately a third of
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parents indicated a significant overall impact of hearing loss on their child’s quality of life. When parental responses to questions about the presence of negative effects of MBHL or UHL on communication, behavior, independence and education of their child were combined and compared with previously collected data from families of children with greater degrees of hearing loss, there was no difference between the perceived impact by the MBHL and UHL groups and the group of children with moderate hearing loss. Clearly, further carefully controlled research is needed regarding the extent to which socio-emotional and functional health problems exist in children with MBHL. Children with minimal to mild degrees of hearing loss may experience more fatigue because increased listening effort is needed to perform at the same level as children with normal hearing on speech recognition tasks.74 To the extent this is true, even children with minimal to mild hearing loss who perform at or above grade-appropriate levels academically might pay a functional health cost for their accomplishments. Considering that the academic achievement of children with MBHL varies greatly, and that adults with MBHL and UHL display a highly diverse range of communication and socio-emotional problems,75 one would expect a group of children with MBHL to be heterogeneous in socio-emotional functional status as well. Kopun and Stelmachowicz76 adapted an adult questionnaire for a group of children ages 10 to 16 years to determine how children with hearing loss perceived the impact of the impairment on their daily function. The results for a group of children with MBHL, most of whom did not wear hearing aid(s), revealed fewer reports of communication or social difficulties when compared with a group of unaided adults with MBHL. Parental responses to the same questionnaire showed poor agreement with the children’s perceptions. The authors proposed that the children with MBHL might have underreported their level of difficulty because they did not want to become hearing aid users, or that parents of children in this age group may not have had opportunities to observe their children in several of the social situations
addressed in the questionnaire. Dodd-Murphy and Murphy65 found that self-ratings on the Listening Inventory for Education77 did not differentiate a group of children with mild hearing loss from a group of children with normal hearing, although there was large variation within both groups. For self-report measures to be useful for assessing individual children, several issues should be addressed in future research, including whether MBHL contributes to inaccuracy in the self-assessment of speech perception function in children, especially under adverse conditions,74,78,79 and the likelihood that children with MBHL might perceive communication or socio-emotional problems but are reluctant to report them because they do not desire intervention. There also remains the possibility that some children are using compensatory strategies and adaptations that optimize their ability to communicate and minimize any perceived restriction of their ability to participate in social interactions.
AUDIOLOGICAL MANAGEMENT OF CHILDREN WITH MBHL AND UHL Most audiologists agree that the audiological management of children with MBHL or UHL must be made on a case-by-case basis. The reason for this approach lies in the fact that although children with minimal hearing loss appear to be at high risk for academic difficulty, it is unclear exactly which children will require some form of intervention and which children will not. Therefore, each child’s hearing, speech-language, psychosocial, and educational development should be observed closely. To monitor a child’s progress, it is of great importance to establish effective communication among the child’s parents, caregivers such as day-care professionals, early interventionists or teachers, and any other family members or professionals who spend time with the child. Each of these individuals can provide important information about the child, and their expertise is essential in maximizing the child’s education and development. The use of functional auditory assessment tools that can be completed by parents, teachers, or, when appropriate, the child might be helpful in targeting potential deficits. Together, these individuals can decide
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if a child needs audiological intervention, which may include acoustic modifications to the child’s environment, preferential seating, the use of FM systems, or the use of hearing aids. It is likely that children with MBHL or UHL will not be fit with hearing technology in infancy, if at all.80,81 This is the result of several factors, including late identification of MBHL and UHL,82 audiological uncertainty, and parental hesitation (see McKay et al83 for a review of the hearing aid fitting considerations in children with MBHL and UHL). The following sections address the use of these technologies in the context of UHL or MBHL.
Hearing Aids for Children with UHL The decision to provide a hearing aid to a child with UHL depends on the severity of the loss, the age of the child, and other factors such as a child’s and family’s motivation for using the device. Although the benefits of monaural hearing aid fittings with children have not been thoroughly documented, it is reasonable to expect that a child would experience some of the advantages of binaural hearing, including improved speech understanding in noise, binaural summation, and improved localization skills. However, the provision of bilateral hearing does not ensure that a listener will enjoy the binaural benefits that are available from two normal-hearing ears. That is, it is possible that by aiding one ear, a reduction in speech perception relative to unaided performance can occur. This phenomenon of decreasing bilateral performance when an individual receives asymmetrical auditory input is referred to as binaural interference.84 Another consideration in fitting amplification to a UHL is that because of possible auditory deprivation effects, the timing for providing a hearing aid to the impaired ear is worth careful consideration. For example, researchers have speculated that binaural hearing is a skill learned early in childhood and cannot be recovered later in life.85 An impaired ear left unaided during infancy and early childhood might limit a child’s binaural hearing abilities should he or she be fitted with a hearing aid later in childhood. However, studies have demonstrated that fitting a hearing aid to an
impaired ear might preserve that ear’s ability to decode sound.86,87 It should be noted that hearing aid compliance tends to be low in children with UHL.88,89 One reason for this low compliance is a delay in fitting,80,81 which might result from a lack of certainty among audiologists regarding the necessity of hearing aid use with UHL. The later a child is fit with amplification, the poorer the compliance.90 Another amplification option designed for children with UHL is the contralateral-routingof-signal (CROS) hearing aid (often referred to as a conventional CROS), including the boneanchored hearing aid (BAHA) and the transcranial CROS. This option is typically reserved for those individuals whose poorer ear is considered to be ‘‘unaidable.’’ The definition of ‘‘unaidable’’ varies among audiologists, however, Valente91 defines such losses as profound, with very poor word recognition ability and a marked intolerance for amplified sound. The conventional CROS hearing aid works by routing signals arriving at the poorer hearing ear to the normal-hearing, or opposite, ear via air conduction. The routing of the signal is accomplished by using a wired or wireless connection between the microphone on the poorer ear and a receiver on the normal-hearing ear. Electromagnetic or FM signals are used to route sounds between microphone and receiver in wireless devices. Despite the common use of conventional CROS hearing aids with adults, children perform better in noise with FM systems than with CROS hearing aids or with no hearing device at all.92,93 However, CROS amplification might be useful to children who need listening assistance outside of school or who do not have access to FM technology. When CROS technology is recommended for children, they should have the maturity and ability to maintain some control over their physical location or head position in the acoustic environment. That is, if a child is positioned such that undesirable noise is directed to the microphone, the child should be capable of repositioning himself or herself to optimize the listening arrangement. More recently, transcranial CROS fittings have gained some popularity. The transcranial fitting requires fitting a high-power in-the-ear, completely-in-the-canal, or behind-the-ear
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hearing aid to the poor ear, with enough output to stimulate the contralateral cochlea via vibration of the skull using an air-conducted signal.94,95 Evidence supporting the use of transcranial fittings in children has been lacking, and their use with adults has been received with mixed results. The BAHA is a surgically implanted device that was originally marketed for those with conductive or mixed hearing loss. The BAHA uses direct percutaneous coupling of the vibrating transducer to a titanium implant anchored in the temporal bone and is now a CROS option for those with UHL.96 For those with UHL, it has been suggested that this device acts as a transcranial hearing aid (also referred to as a true transcranial CROS). That is, sound is received at the microphone of the BAHA on the poorer ear but is transmitted via bone conduction to the contralateral cochlea. The data on the use of the BAHA for UHL are limited. In short, adult studies have demonstrated no improvement on localization tasks, some improvement for understanding speech in noise, and subjective reports of benefit.97–100 Although the BAHA is approved by the Food and Drug Administration for children as young as 5 years of age, the use of this device as a transcranial CROS with children should be approached with caution.
Hearing Aids for Children with MBHL The American Academy of Audiology Pediatric Amplification Protocol101 has recommended that target values for gain and output be determined by prescriptive methods such as the Desired Sensation Level approach.102 This is particularly true for children with MBHL to avoid overamplification. For infants and young children with MBHL, it is important to consider that once the real-ear-to-coupler difference is taken into account, the prescribed gain across frequencies may be minimal and more easily achieved by other measures. That is, small levels of gain can be obtained by raising the volume of a talker’s voice or decreasing the speaker-listener distance. Another consideration in the fitting of amplification on children with MBHL is that the amount of gain a child will receive from a
hearing aid should be weighed against other factors such as the amount of circuit noise a child might hear. For minimal degrees of hearing loss, the amount of benefit from amplification might be negated by the amount of lowlevel noise emitted by the hearing aid.103,104 Through the use of survey instruments, Davis and colleagues104 revealed that 44% of children with mild bilateral hearing losses wore their hearing aids all the time, 3% wore them only for school, and 25% never wore them. These findings suggest that traditional hearing aids should remain only one of several options for children with MBHL and support the notion of making management decisions on a case-by-case basis.
FM Technology Because of the difficulties noted previously of children with UHL and MBHL listening in the presence of background noise, FM technology has gained popularity as a management option of choice for children with MBHL and UHL, especially in classroom settings. FM receivers are available in ear-level, portable desktop, or sound field arrangements. By improving the SNR, speech perception is improved beyond that attained by the use of CROS hearing aids or no amplification at all.64,92,93 In 2004, Tharpe and colleagues64 examined various earlevel FM configurations with children with minimal and mild degrees of hearing loss. Monaural FM fittings were equally beneficial to speech perception ability as bilateral FM fittings in the majority of the test conditions. Moreover, the children overwhelmingly preferred wearing one ear-level FM device rather than two. These findings suggest that it is reasonable to recommend a monaural FM fitting with children who have minimal or mild bilateral hearing loss. Such an arrangement leaves one ear unoccluded and available to hear speakers who are not using a FM transmitter while significantly improving speech recognition ability relative to no intervention.
CONCLUSIONS Collectively, evidence supports the conclusion that children with permanent UHL and
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MBHL are at significant risk for academic and behavioral problems. Perhaps one of the most puzzling questions remaining is why some children with minimal degrees of hearing loss experience little if any psychoeducational difficulty while others struggle. Nance105 reported that cytomegalovirus (CMV) is the leading cause of prelingual unilateral hearing loss in children in the United States. He went on to posit that the poor academic performance of these children may be the result of the neurological deficits associated with CMV. To date, we do not have any evidence to support a relationship between outcomes of children with minimal degrees of hearing loss and their etiologies. In fact, we still have little information about the etiologies of minimal degrees of loss. This remains an area deserving of additional inquiry. Another important area of further research is the determination of appropriate and effective intervention strategies for children with UHL and MBHL. In 2005, a workshop was convened by the Centers for Disease Control and Prevention, Early Hearing Detection and Intervention program, and the Marion Downs Hearing Center to address concerns about the identification and management of children with minimal to mild degrees of hearing loss. Proceedings from that meeting describe the current state of our knowledge in this area and outline the need for further research.106
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