There has recently been a renewed interest in the topic of minimal and mild hearing loss in children. Although the term "minimal hearing loss" has not been standardized, the Bess, Dodd-Murphy, and Parker (1998) definitions are commonly used and include:
Mild bilateral hearing loss - pure tone average at .5, 1.0, and 2.0 kHz between 20 and 40 dB hearing level (HL);For purposes of this review, only permanent, not transient, hearing loss is considered.
High-frequency hearing loss - pure tone thresholds worse than 20 dB HL at two or more frequencies above 2.0 kHz;
Unilateral hearing loss - pure tone average at .5, 1.0, and 2.0 kHz worse than or equal to 20 dB HL or pure tone thresholds worse than 25 dB HL at two or more frequencies above 2 kHz in the affected ear, with normal hearing in the contralateral ear.
Prieve et al. (2000) reported 1 in 1000 infants are identified with unilateral hearing loss (UHL) as a newborn; whereas, Bess et al. (1998) reported 3 in 100 school-aged children have UHL. This difference in prevalence rates of UHL between the newborn and school age periods may reflect poor follow-up rates from newborn screening programs resulting in fewer confirmed hearing losses, different screening criteria and definitions among hospitals and schools, progression of a mild hearing impairment, a late-onset hearing loss, or a combination of these factors. In any case, UHL is the most prevalent configuration of permanent hearing loss in school-aged children (Bess et al., 1998). When considering all configurations of permanent minimal and mild bilateral hearing loss (MBHL), as well as UHL, the prevalence increases to 5.4% of school-aged children.
Academic, Social, and Behavioral Outcomes
Unilateral hearing loss.
Two decades ago, a flurry of research was conducted examining the effects of UHL on children (Bess & Tharpe, 1986; Bess, Tharpe, & Gibler, 1986; Bovo et al., 1988; Culbertson & Gilbert, 1986; Jensen, Børre, & Johansen, 1989; Keller & Bundy, 1980; Klee & Davis-Dansky, 1986; Oyler, Oyler, & Matkin, 1988; Stein, 1983). Researchers at Vanderbilt University examined a cohort of 60 school-aged children with UHL (Bess & Tharpe, 1986). Most of their hearing losses were identified at five or six years of age upon school entry with some identified as late as 12 years of age. Interestingly, approximately 37% of these children failed at least one grade in school, and an additional 13% required academic assistance or resource help. This grade failure rate was ten times that of the general school population for that geographic area. Also of interest was that the majority (62%) of the children who failed a grade had hearing loss in the right ear. In addition, children were at a higher risk for academic difficulty if the hearing loss was of a severe degree when compared to those children with lesser degrees of loss.
Upon closer examination of 25 of the original cohort of 60 children, Bess et al. (1986) found that children with UHL had more difficulty with speech understanding in the presence of background noise than their matched peers with normal hearing. Furthermore, even when the desired speech stimuli were directed toward the children's better ear in quiet conditions, the children with UHL still performed more poorly than their normal-hearing peers. Twenty percent of the children with UHL were also reported to have more behavior problems than their peers with normal hearing (Bess & Tharpe, 1986).
Currently, newborn hearing screenings accommodate earlier identification of UHL, and a growing number of individuals in the hearing health care and education settings are more aware of the risk for academic difficulties experienced by these children. One might expect that outcomes would improve over time; however, recent examination of the status of school-aged children with UHL suggested that 30-55% are still having academic difficulty (Brookhauser, Worthington, & Kelly, 1991; English & Church, 1999), regardless of the fact that it appears more of these children are receiving intervention than ever before (McKay, 2002; Reeve, Davis, & Hind, 2001).
Minimal and mild bilateral hearing loss.
Similar to children with UHL, early studies of children with permanent MBHL revealed difficulties in the academic setting (Blair, Peterson, & Viehweg, 1985; Davis, Elfenbein, Schum, & Bentler, 1986; Quigley & Thomure, 1968; Sarff, 1998). In fact, one study showed remarkably similar grade failure rates by children with MBHL (37%) to those found in the earlier UHL studies (Bess et al., 1998). More specifically, using the Comprehensive Test of Basic Skills - 4th Edition (CTBS; MacMillan/McGraw-Hill, 1993), children with UHL and MBHL in the third grade demonstrated significantly lower skills than their normal hearing counterparts for the subtests of reading vocabulary, language mechanics, word analysis, spelling, and science. No differences were noted between the sixth and ninth grade groups. Other, more recent studies of academic achievement in children with MBHL have also documented significant difficulty (Teasdale & Sorensen, 2007; Wake & Poulakis, 2004).
In addition to academic achievement, Bess et al. (1998) examined functional health of children with UHL and MBHL using the Cooperative Information Project Adolescent Chart Method (COOP; Nelson et al., 1987). These charts were designed to extract self-reported data in physical, emotional, and social function domains. Results indicated significantly more dysfunction for the children with UHL and MBHL when compared to their peers with normal hearing in the energy domain. That is, the children with minimal hearing loss reported less energy and greater fatigue more frequently than their peers with normal hearing.
To explore this reported low energy concept in more detail, Hicks and Tharpe (2002) conducted a dual-task study of school-aged children with MBHL designed to assess listening effort. The primary task was speech perception in noise while the secondary task was a button press in response to a light coming on. The rationale behind this design was that if one has a limited effort capacity, then when energy is exerted for a primary task, less energy is available for a secondary task, resulting in poorer performance. The study demonstrated that the children with MBHL performed significantly poorer on the secondary task than their age- and grade-matched peers with normal hearing, indicating greater exertion of energy during the listening task. This result may account, in part, for the reports of lower energy in children with MBHL. Furthermore, low energy and greater fatigue can contribute to and/or be misconstrued as behavioral issues in the classroom.
Audiological Management
Many questions abound regarding when, or if, a child with UHL should receive amplification. The Pediatric Working Group (1996) and, more recently, the American Academy of Audiology (2003) have recommended considering hearing aid technology for children with UHL on a case-by-case basis. Consideration should be given to the child's health, cognitive status, and functional needs when making this decision with the family. At present, there are multiple devices that can be considered for children with a unilateral hearing loss including traditional amplification, CROS hearing aids, bone anchored hearing aids, and FM systems.
Studies vary widely in the percentage of children with UHL who receive traditional amplification (9-48%; Davis, Reeve, Hind, & Bamford, 2002; English & Church, 1999). Furthermore, of those who actually receive hearing aids, wearing compliance is not as high as in children with bilateral hearing loss. In one study of children with UHL, approximately 26% of children with UHL compliantly used their hearing aid full-time; whereas, 72% of children with a moderate bilateral hearing loss actively used their hearing aid full-time (Reeve, 2005). This difference may be because children with UHL tend to be fitted with hearing aids later than children with bilateral hearing loss, and wearing compliance is typically poorer when children are fitted later (Reeve, 2005).
Contralateral routing of signal (CROS) hearing aids are often considered an amplification option when a child's poorer ear does not have sufficient hearing for traditional amplification. Although potentially useful for adults with UHL, studies show CROS aids are not as effective for school-aged children (Kenworthy, Klee, & Tharpe, 1990). The primary argument against fitting children with CROS hearing aids is that children are unable to position themselves (i.e., the hearing aid microphone) to maximize benefit in noisy environments. That is, children may not have the maturity to adjust their location or head position within a classroom or other environment if noise is being directed to the microphone, thus interfering with speech perception.
Bone-anchored hearing devices have been approved through the United States Food and Drug Administration for use in children five years of age and older. These are surgically-implanted bone-conduction devices for patients with a moderate-to-severe conductive or mixed bilateral hearing loss or an UHL. There are various reports of bone-anchored fittings on adults with UHL, with results ranging from no improvement in localization, to improvement of speech in noise and subjective reports of benefit (Spitzer, Ghossaini, & Wazen, 2002; Wazen, Spitzer, Ghossaini, Kacker, & Zschommler, 2001). However, at this time, there are little data to support their use in young children.
Similarly to children with UHL, it has been recommended that children with MBHL be considered for amplification on a case-by-case basis (AAA, 2003; Pediatric Working Group, 1996). One of the obstacles to fitting such losses is that audiologists seem to be uncertain about the diagnosis of MBHL, and this uncertainty can lead to delays in the fitting of amplification. Although this hesitation can be related to inconsistent patient cooperation in the pediatric population, resulting in more follow-up testing, some of the diagnostic uncertainty is the result of a lack of calibration procedures across diagnostic equipment and couplers. In other words, there is no standard calibration procedure for ABR systems and so different transducers require different couplers for calibration. It is up to the audiologist to ensure that proper calibration procedures have been followed for a specific ABR system. Regardless of the cause, as stated previously, there is some evidence to suggest that the later children are fitted with hearing aids, the poorer the wearing compliance (Reeve, 2005). In one study, only 44% of children with MBHL wore their hearing aids all day as compared to 72% of children with moderate bilateral hearing loss.
The literature clearly illustrates that adverse listening environments negatively affect the speech perception of children with UHL and MBHL (Bess et al., 1986; Crandell, 1993); therefore, another viable hearing technology option for children with UHL or MBHL is frequency-modulated (FM) systems. Through the use of remote microphone technology, children can receive a FM signal to a personally-worn receiver, thus reducing the impact of background noise, reverberation, or speaker-to-listener distance. Personal low-gain FM systems can be fitted on normal to near-normal hearing ears. However, many questions concern audiologists with the fitting of these devices, especially if they are to be used in classroom settings. Choices include personally-worn (either an ear level or body worn device) or sound field FM systems (the signal is transmitted to strategically placed loudspeakers throughout the room), unilateral or bilateral fittings, and the type of coupling or earmolds that are appropriate. Of particular concern is how these decisions might impact a child's access to "overhearing" his or her schoolmates and participating in classroom discussions. With those concerns in mind, Tharpe, Ricketts, and Sladen (2004) rotated a cohort of school-aged children with UHL and MBHL through various fitting configurations. Testing was completed with an ear-level FM device fit monaurally or bilaterally with either an open or a skeleton earmold. Each configuration was worn for two weeks, followed by speech perception in noise testing. As expected, there was a significant improvement in speech perception when children were in an FM condition as compared to a non-FM condition (average 8.3 dB signal-to-noise advantage). On average, there was a 2.0 dB advantage when wearing a skeleton versus an open earmold and a 2.2 dB binaural advantage. Despite the evident binaural advantage, the majority of the subjects reported that they preferred the unilateral configuration. The authors concluded that there can be flexibility in terms of the fitting configurations based on individual student needs and the classroom environment while still maintaining significant speech perception benefit.
A number of professionals advocate the use of sound field FM as another option for children with minimal degrees of hearing loss in classroom settings. As with personal FM systems, the purpose of sound field FM is to reduce the detrimental effects of background noise and reverberation, thus enhancing the signal-to-noise ratio. Research shows improvements in speech perception for children with MBHL when using sound field FM systems (Blair, Myrup, & Viehwig, 1989; Neuss, Blair, & Viehweg, 1991). Other advantages of sound field FM systems include the following:
- An enhanced speech signal benefits all the children in the classroom, including those who might have unidentified hearing loss, temporary or conductive hearing loss secondary to otitis media with effusion, as well as other learning and behavioral disorders
- No single child is stigmatized by having to wear a personal device
- Any dysfunction of the equipment is immediately apparent to the teacher.
It may be helpful to utilize functional auditory assessment tools that engage caregivers in specific observational activities that can demonstrate their child's listening skills in real-world settings. Functional auditory assessments evaluate listening behaviors outside the confines of the soundproof booth where most formal audiological testing takes place. These tools can take the form of self assessments (for older children) and/or parent and teacher questionnaires. There are also tools designed specifically for children with minimal degrees of hearing loss such as the Screening Instrument for Targeting Educational Risk (SIFTER; Anderson, 1989) or the Children's Home Inventory for Listening Difficulties (CHILD; Anderson & Smaldino, 2000).
Conclusions
Over the past several decades, we have learned a great deal about children with UHL and MBHL. That knowledge has resulted in an increased level of monitoring and intervention for these children; however, there is still a great deal to learn. For example, at this time, we cannot predict which of these children will experience academic difficulty and we have much to learn about the effectiveness of our intervention strategies. It is likely that through the combined efforts of audiologists, speech-language pathologists, otologists, and educators, we will refine our management practices and improve outcomes for children with UHL and MBHL.
More About the Topic
Audiologists are often faced with the predicament of appropriate treatment for children with UHL and MBHL. Although this is not a new topic, it is an important subject to consider. Appropriate treatment is possible by recognizing that these individuals may need additional assistance and through open communication with the family and other professionals involved in the child's care. Parents of children with UHL and MBHL should be informed of possible difficulties their child may experience at home, school, and during after school activities. In addition, it is helpful for parents to be aware of good communication strategies. Most importantly, once a decision is made about amplification for a child with UHL or MBHL, there should be no delay in proceeding with these intentions.
As stated above, this article did not address transient, fluctuating, or non-permanent hearing loss; however, depending on the severity and longevity of the condition, these children may also demonstrate difficulty hearing in the classroom. In addition to preferential seating in the classroom, children with these conditions may benefit from supplementary assistance. Parents should be encouraged to inform their child's teacher about any ongoing or fluctuating hearing difficulties their child might be experiencing due to otitis media or other middle ear pathologies. In addition, children with a long standing unilateral or mild bilateral conductive hearing loss requiring surgery at a later time (i.e. when the child has reached a developmental plateau), may necessitate amplification, particularly in the classroom, until surgery is an option. Similarly to children with UHL and MBHL, it is important to make decisions about amplification and/or additional assistance for these children on a case-by-case basis.
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