Unilateral and Mild Bilateral Hearing Loss in Children: Past and Current Perspectives

Psychoeducational Effect of Unilateral Hearing Loss

The first step in investigating the effect of UHL on children was to characterize the population and determine just how widespread the problem might be, if there was indeed a problem. Some of the earliest investigations began with Bess and Tharpe at Vanderbilt University when they collected descriptive data via medical and educational case histories on a population of 60 children with sensorineural UHL living in middle Tennessee. ³ All 60 children had been diagnosed with UHL of 45 dB or greater (.5, 1.0, 2.0 kHz) in the poorer ear and thresholds no worse than 15 dB (.5, 1.0, 2.0 kHz) in the normally hearing ear. These children ranged in age from 6 to 18 years. Approximately 52% of these children had no known etiology for their hearing loss. The most frequently cited suspected etiologies were viral complications (24%), meningitis (15%), and head trauma (8%). Table 1 provides a distribution of the ages at which these unilateral losses were identified.

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Table 1.

Distribution of Ages at Which 60 Children Were Identified With Unilateral Hearing Loss

Age Category	Percentage
1–2 years	3
3–4 years	20
5–6 years	50
7–8 years	20
9–10 years	5
11–12 years	2

Source: Adapted with permission from Bess and Tharpe (1984). ⁴

The mean age of identification was approximately 5½ years; only 23% of children with UHL were being identified before the age of 5 years, quite late by today's standards. At that time, of course, routine newborn hearing screening had not yet made its entrance. These results suggested that the losses were identified on the children's entrance to school and their participation in school hearing-screening programs.

Perhaps the most noteworthy of the findings from these 60 children was the revelation that only half were performing satisfactorily in school. As summarized in Table 2, 35% of the children had repeated at least 1 grade in school, and an additional 13.3% required resource assistance such as academic tutoring. This was especially concerning given that the failure rate in that metropolitan area for the general elementary school population was only 3.5%.

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Table 2.

Academic and Behavioral Standing of 60 Children With Unilateral Sensorineural Hearing Loss

Academic Standing	Percentage
Satisfactory	51.7
Resource help required	13.3
Grade repetition required	35.0
Behavior problem as determined by teacher
Yes	20.0
No	80.0

Source: Adapted with permission from Bess and Tharpe (1986). ³

Furthermore, 20% of the 60 children were identified by their teachers as exhibiting behavior problems. All of these children were receiving preferential classroom seating, the management option of choice at that time. A short time later, our colleagues at the University of Arizona ⁵ and our European colleagues ^6,7 published strikingly similar educational results on school-aged children with UHL. A summary of the early academic trends found for children with UHL is presented in Table 3.

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Table 3.

Early Academic Findings on Children With Permanent Unilateral Hearing Loss

Investigation	Failed (One or More) Grades	Resource Help (One or More Years)	Combined
Bess and Tharpe 3	35%	13%	48%
Oyler et al 5	27%	41%	68%
Bovo et al 6	22%	12%	34%
Jensen et al 7	18%	60%	78%

At about this same time, Julia Davis and her colleagues at the University of Iowa published the findings of a group of school-aged children with hearing loss including UHL. ⁸ They identified a slight decrement in verbal intelligence quotient (IQ) scores in the children with UHL relative to their performance IQs. Furthermore, achievement-test scores in reading, math, and spelling approximated the 50th percentile but were not related to the degree of the unilateral loss. That is, whether a child's UHL was mild, moderate, or profound, the average scores on achievement tests were relatively similar. In contrast, Culbertson and Gilbert ⁹ did not find significant differences between children with UHL and their normal-hearing peers on tests of IQ as measured by the Wechsler Intelligence Scale for Children—Revised (WISC-R) ¹⁰ and the Hiskey-Nebraska Test of Learning Aptitude. ¹¹ However, when comparing the IQ scores of children with severe to profound UHL to those of children with mild to moderate UHL, those with more severe degrees of UHL had significantly lower full-scale IQs than those with lesser degrees of UHL. Furthermore, similar to the findings of Davis et al, Culbertson and Gilbert ⁹ found significantly lower scores on the subtests of word recognition and spelling of the Wide Range Achievement Test ¹² in children with UHL as compared to their normal-hearing peers.

Early studies of children and adults with UHL suggested the potential for psychosocial problems. ^13–15 In 1967, Giolas and Wark ¹³ reported that adolescents with UHL experienced feelings of embarrassment, annoyance, confusion, and helplessness. As noted previously, 20% of the children in the Bess and Tharpe ³ study were described by their teachers as having behavior problems, whereas Keller and Bundy ¹⁴ also reported that teachers observed uncooperative and inattentive behavior in school-aged children with UHL. Furthermore, using standardized scales, Stein ¹⁵ obtained behavior ratings from parents and teachers of a small group of school-aged children with UHL. Excessive behavior problems including social withdrawal and aggression were reported in 42% of these children. An assessment of verbal and nonverbal learning abilities revealed that 37% of these children scored significantly below an acceptable range relative to normal-hearing children in the areas of interpersonal and social adjustment. It should be noted that all of these children were performing adequately academically. This finding of teacher reports of behavioral and attentional difficulties in children with UHL was confirmed almost a decade later by another research group. ¹⁶ Self-perceived hearing handicap was examined in a group of adults with UHL. ¹⁷ Although considerable intrasubject variability was reported, a substantial number of these subjects expressed feelings of being frustrated, upset, and left out.

Of interest today is whether the studies of the 1980s triggered any educational or management changes that have resulted in improved outcomes for children with UHL. Recent reports suggest that indeed, there has been increased interest among professionals to provide audiological management to children with UHL. ^18,19 However, several studies since the 1980s have documented the unrelenting below-average academic performance of children with UHL. ^16,20,21 A survey of 26 educational audiologists, who served a total of 423 children with UHL, revealed that 26% of these children used hearing aids, frequency-modulation systems, or a combination thereof. ²¹ In addition, 54% of these children were receiving special education services (ie, amplification monitoring, resource assistance, speech-language services). The authors concluded that despite an increased awareness of the high-risk status of children with UHL and increased intervention with these children relative to that of the 1980s, the proportion of children with UHL performing at below-average academic level had not changed. Results such as these certainly beg the question of whether factors other than auditory accessibility are contributing to the less than optimal academic performance.

Speech, Language, and Auditory Characteristics of Children With Unilateral Hearing Loss

The educational findings from Bess and Tharpe's study of 60 children with UHL prompted a closer look at the audiological characteristics of a subgroup of 25 of those children who were closely matched to 25 peers with normal hearing. ²² Bess and colleagues examined the localization and speech-recognition abilities of these matched pairs of children, and predictably, they found that the localization scores were significantly poorer for the children with UHL than for the children with normal hearing. These localization difficulties increased as the degree of UHL increased. As seen in Figure 1, the children with UHL also had significantly poorer speech-recognition scores than their normal-hearing counterparts. This was true whether the test was conducted in quiet or noise and whether the speech stimuli were directed toward the poorer ear (monaural indirect condition with noise directed toward the normal-hearing ear) or toward the normal-hearing ear (monaural direct condition with noise directed toward the poorer hearing ear).

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Figure 1.

Mean sound-field composite scores in percentage correct on the Nonsense Syllable Test (Levitt and Resnick ²³ ) across several primary-to-secondary ratios (ie, signal-to-noise ratio) for children with UHL (n = 25) and children with normal hearing (n = 25). Reprinted with permission from Bess and colleagues (1986). ²²

Similarly, numerous studies have demonstrated poor localization ability in children with UHL relative to children or adults with normal hearing in both ears. ^6,24,25 Other research groups have documented poor speech-recognition performance of children with UHL when measured in the presence of background noise. ^6,26 For example, Bovo et al ⁶ found significantly poorer speech-recognition performance for a group of children with UHL as compared to their normal-hearing peers, even in a monaural direct condition. This was the case whether the child had left or right ear impairment. Ruscetta and colleagues ²⁶ also examined performance of school-aged children with severe to profound UHL on speech-recognition tasks as compared to 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 than children with normal hearing. This difficulty with speech perception in noise was observed for nonsense syllable and sentential speech materials.

Specific speech and language deficits have not been clearly identified in children with UHL. Klee and Davis-Dansky ²⁷ performed a battery of standardized language tests with the Bess subgroup of 25 children with UHL and their normal-hearing peers. Although Klee and Davis-Dansky did not identify any specific language impairment in either group, they found that the children with UHL who had failed a grade in school had significantly lower verbal IQ scores than those children with UHL who were academically successful. However, both the academically successful and the unsuccessful UHL groups had verbal IQs within the normal range. Tieri and colleagues ²⁸ were also unable to identify any speech or language problems from case-history reports obtained from parents of children with UHL. However, most parents surveyed reported that their children had learning problems. Likewise, other investigations of school-aged children with UHL have found no differences in language abilities when compared to children with normal hearing. ^29,30 Taken together, the results of speech and language assessments in children with UHL have not revealed any specific deficits.

Psychoeducational Effect of Mild Degrees of Bilateral Hearing Loss

Early studies of children with mild degrees of hearing loss suggested that these children were not performing at expected academic levels. ^31–34 For example, Quigley and Thomure, ³³ in examining academic records of school-aged children, revealed a systematic progression in academic difficulty with increasing degrees of hearing loss. Even children with hearing thresholds between 15 and 26 dB were found to have a 1.11-grade delay between their expected grade performance and their actual grade performance. Blair et al ³¹ examined the educational performance of 24 school-aged children with mild bilateral sensorineural hearing loss compared to 24 children with normal hearing. On several of the subtests of the Iowa Test of Basic Skills, Blair found that third- and fourth-grade children with hearing loss scored poorer than their normal-hearing peers.

Those findings, along with the findings from the earlier Vanderbilt UHL studies, encouraged Bess and colleagues ³⁵ to take a closer look at children with all types of “minimal” hearing loss, including those with unilateral and bilateral impairment. They sampled 1228 children in the third, sixth, and ninth grades. For purposes of that study, minimal hearing loss included (1) unilateral sensorineural hearing loss, defined as average air-conduction thresholds (.5, 1.0, 2.0 kHz) ≥20 dB HL in the impaired ear, an average air-bone gap no greater than 10 dB at 1.0, 2.0, and 4.0 kHz, and average air-conduction thresholds in the normal-hearing ear ≤15 dB HL; (2) bilateral sensorineural hearing loss, defined as average pure-tone thresholds between 20 and 40 dB HL bilaterally with average air-bone gaps no greater than 10 dB at frequencies 1.0, 2.0, and 4.0 kHz; and (3) high-frequency sensorineural hearing loss defined as air-conduction thresholds greater than 25 dB HL at 2 or more frequencies above 2 kHz (ie, 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.

A total of 66 children met 1 of those hearing-loss criteria. The Comprehensive Test of Basic Skills (CTBS), fourth edition, ³⁶ was used to assess educational performance. Children with minimal hearing loss in the third grade demonstrated significantly lower skills than their normal-hearing counterparts for the subtests of reading vocabulary, language mechanics, basic battery, word analysis, spelling, and science. No differences were noted between groups for the sixth and ninth graders. The average grade-retention rate for all of the children with minimal loss was 37%. The retention rates for children in each grade are summarized in Figure 2. Note that these retention rates are significantly higher than the district norm rates at each grade level. Therefore, despite the fact that the older children in that study demonstrated a normal aptitude for educational performance (based on CTBS results), they still experienced difficulty in school.

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Figure 2.

School retention rates for children with minimal sensorineural hearing loss (MSHL) at each grade level (3, 6, 9). School-district norm retention rates are included for comparison. Asterisks denote the grades in which significance (P < .05) was achieved between groups. Reprinted with permission from Bess and colleagues (1998). ³⁵

Bess and colleagues also assessed the functional health status of the children with minimal losses in the sixth and ninth grades by using the Cooperative Information Project Adolescent Chart Method (COOP). ^37,38 This chart is designed to extract data in the domains of physical, emotional, and social functionality. The COOP scores indicated significantly more dysfunction for the children with minimal hearing loss as compared to their normal-hearing peers in the energy domain. That is, the children with minimal hearing loss reported having less energy or were tired more frequently than their normal-hearing peers. Additionally, the ninth graders with minimal hearing loss demonstrated significantly more dysfunction in the domains of stress, social support, and self-esteem than the children with normal hearing.

Speech, Language, and Auditory Characteristics of Children With Mild Degrees of Bilateral Hearing Loss

There were ample early data to suggest that children with MBHL may have difficulty listening in the presence of background noise relative to their normal-hearing peers. ^39–43 However, most of those studies included subjects with greater degrees of hearing loss than those who are the focus of this review. For example, more favorable signal-to-noise ratios are required for equivalent performance on speech-perception tasks for individuals with mild to moderate hearing loss than for those who have normal hearing. ³⁹ More recently, Crandell ⁴⁴ examined the speech-recognition ability of school-aged children with minimal sensorineural hearing loss (thresholds between 15 and 30 dB bilaterally) and children with normal hearing. The speech-recognition scores of the children with hearing loss were significantly poorer than those of the normal-hearing children under most of the listening conditions. Although there was little if any difference between groups in quiet, as the signal-to-noise ratio became more adverse (ie, from +6 S:N to −6 S:N), the difference between groups became greater.

Prompted by the finding of decreased energy and increased stress reported by the children with minimal hearing loss, Bourland-Hicks and Tharpe ⁴⁵ examined listening effort and fatigue in children with minimal to moderate degrees of hearing loss when listening in a variety of signal-to-noise levels. Although no differences on measures of fatigue were found between the groups of normal-hearing children and children with hearing loss, between-group differences were noted on a dual-task paradigm designed to examine listening effort. Specifically, the children with hearing loss expended more effort in listening to speech in quiet and in the presence of background noise than did the children with normal hearing. Given that listening effort refers to the attention requirements necessary to understand speech, ^46,47 the implication of these findings is that children with even a relatively mild degree of hearing loss may exert more energy than their normal-hearing peers to listen in a classroom setting, thus leaving them with less energy or attention capacity for processing what they hear, taking notes, and other activities required of school children.

Speech and language assessments of children with minimal degrees of bilateral hearing loss have been lacking. Most studies have examined children with minimal bilateral hearing loss as part of a larger group of children with greater degrees of loss. For example, in a comparison of school-aged children with mild, bilateral sensorineural hearing loss (25 to 45 dB in the better ear) to their normal-hearing peers, Blair and colleagues ³¹ revealed that the academic performance of children with mild hearing loss lagged behind that of their normal-hearing peers, especially in the areas of vocabulary, reading comprehension, and language use. Furthermore, Briscoe et al ⁴⁸ compared a group of children with mild to moderate bilateral sensorineural hearing loss to children diagnosed with specific language impairment (SLI). They found that the children with hearing loss were as impaired as the children with SLI who had normal hearing on tests of phonological discrimination, phonological awareness, and non-word repetition. However, the children with mild to moderate hearing loss did not demonstrate deficits in language and literacy that characterize SLI. In another examination of children with mild degrees of hearing loss (<45 dB pure tone average [PTA] bilaterally), Davis and colleagues ³² found receptive vocabulary, verbal ability, and reasoning to be more than 1 standard deviation below the mean. It was of interest to note that the children with mild hearing loss in that study performed similarly to other study participants who had greater degrees of hearing loss (ie, PTA between 45 and 60 dB and PTA ≥ 61 dB).

In another study, Elfenbein et al ⁴⁹ examined the oral language skills of school-aged children with varying degrees of hearing loss. Children with mild hearing loss and those with normal hearing had similar semantic and syntactic skills. However, pragmatic errors and misarticulations were more prevalent in children with MBHL than those with normal hearing. Also of note in that study was that 66% of the children with MBHL self-reported that they had difficulty making themselves understood at times. They referred to speech errors, lack of vocabulary, and difficulty with correct word order as factors in their expression. This finding is similar to that from a more recent survey of parents of children with MBHL. Forty percent of respondents in that survey reported that their children had more difficulties than expected producing certain speech sounds. ⁵⁰ Moreover, 15% reported that it was often or very often difficult to understand their child's speech.

In a recent population-based study by Wake et al, ⁵¹ no statistically significant differences on tests of language, reading, and behavior were found for a large cohort of children with slight or mild sensorineural hearing loss when compared to those with normal hearing. However, phonological short-term memory and phonological discrimination were poorer in the children with hearing loss than in those with normal hearing. These findings are consistent with the earlier Briscoe et al ⁴⁸ findings. Difficulty with phonologic short-term memory has been associated with difficulties in reading in studies of children with and without hearing loss. ⁵²

Where Do We Go From Here?

During the past several decades, much has been learned about the effect of UHL and MBHL on children. Collectively, the data suggest that children with UHL and MBHL are at risk for psychoeducational and psychosocial deficits. But many questions still remain unanswered. Key questions include the following: