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The Significance of Prelingual Conductive Hearing Loss for Auditory and Linguistic Development of Aboriginal Infants

Terry Nienhuys
Menzies School of Health Research, Darwin

From: Conference Proceedings Medical Options for Prevention and Treatment of Otitis Media in Australian Aboriginal Infants
Menzies School of Health Research and the Australian Doctors Fund
Darwin, Northern Territory Australia
16-18 February 1992

Contents

Introduction

Psycho-educational and Communication Developmental Effects of CHL Suggested models of the effects of CHL Evidence from studies of non-Aboriginal Children

Effects Of CHL On Development Of Indigenous Children The special case of Aboriginal children The significance of fluctuating conductive hearing loss in early infancy

Conclusion

Figures

References

 

Introduction

There is now an extensive literature concerning the possible effects of early otitis media (OM) and concomitant conductive hearing loss (CHL) on auditory, language and social skills acquisition by the developing child (see Haggard and Hughes (1991) for review). While aspects of the question remain controversial, there is a consensus that the intermittent CHL associated with early childhood OM does affect children's development, although there is still little agreement on the precise nature of the effects. However, since this seminar is primarily concerned with the microbiology and otology of the very early onset, aetiology, severity, natural history and treatment of OM in Australian Aboriginal infants, this paper will argue that Aboriginal infants are at increased risk for a number of reasons, and that their middle ear disease should be regarded as a potentially serious threat to their subsequent development that warrants early and aggressive treatment.

This will be done by:

1. Briefly summarising the literature concerning the effects of OME on linguistic and educational development of non- Aboriginal children, and highlighting the social and educational contexts of Aboriginal children's OM which place them at increased developmental risk.
2. Considering current evidence for early onset and natural history of OM, and likely associated CHL levels in Aboriginal infants.
3. Reviewing psycho-acoustic and auditory physiological studies which suggest detrimental effects of early childhood CHL and auditory sensory deprivation on the development of lower levels of the auditory pathway and, consequently, psycho-acoustic and linguistic skills development.

Psycho-educational and Communication Developmental Effects of CHL

• Suggested models of the effects of CHL
• Evidence from studies of non-Aboriginal Children

Suggested models of the effects of CHL

A number of models have been proposed to explain the likely subtle relationship between OM, CHL and the auditory, social and linguistic development of affected children. On the basis of her previous studies, Feagans has suggested a "best guess" (Page 198) model for the link between OM, CHL and later language acquisition (Feagans, 1986) as shown in Figure 1. That is, early childhood CHL induces initial difficulties in syntactic, semantic and phonological skills development, but also, and more importantly, a habit of inattention to auditory signals, especially speech. When hearing is restored, the language skills may recover, but, without intervention, persisting difficulties in attention lead to persistent language, learning and social difficulties. Lowell (1991) has extended this model considerably to show how the Aboriginal child who attends a bilingual and/or bicultural classroom setting may be further disadvantaged as a result of OM-induced difficulties in auditory skills, linguistic (including metalinguistic) and communicative skills, and social skills.

Both of these models depend upon a growing understanding of the role of audition and of the effects of intermittent mild to moderate hearing loss in the developing child; these effects may operate directly or indirectly as shown in Figure 3. In particular, early auditory deprivation from OM may threaten the development of all four levels of auditory function as described by Erber (1985). First, detection skills are affected by reduced auditory acuity as well as reduced skills in sound localisation, reduced ability to detect signals in noise and, consequently, by poorly developed skills in sustaining auditory attention. Second, auditory discrimination skills are affected, causing children difficulties in discriminating, for example, speech sounds such as /p/ and /b/ as will be discussed below. Consequent deficits in higher order skills such as word identification (and the ability to identify words in the context of other words such as in sentences) and word comprehension are also predicted and reported in experimental studies as cited below. Since developments in these auditory skills are interdependent, operating in a top-down/bottom-up way, CHL may be seen to threaten the range of auditory language skills. Thus, Downs (1988) has argued that the auditory deprivation resulting from early childhood CHL can lead to auditory perceptual problems and central auditory processing deficits which, in turn, lead to auditory language difficulties and language learning delays. The CIAL may also affect the acquisition of syntactic, semantic, phonologic, metalinguistic and social skills directly as shown in the figure, and this may be especially true of the second language which the Aboriginal child is learning in the classroom, as argued by Lowell (1991) and by Nienhuys and Burnip (1988). That is, intermittent CHL may result in reduced or impoverished language input and adult- child interactions which are known to be essential to language acquisition. The resultant delays or difficulties in language and social skills development may further indirectly affect the development of auditory language skills as shown in Figure 3, exacerbating the child's difficulties in auditory and language skills acquisition even further.

Evidence from studies of non-Aboriginal children

The possible effects of CHL on early communication and psycho-social development and on the subsequent educational performance of children with histories of middle ear disease have been the subject of considerable controversy. Studies have attempted to clarify whether there are measurable effects of CHL on child development and emerging language skills, and if so, what degree, configuration and duration of hearing loss is critical? In other words, what is the dose-response relationship between CHL and communication development, and how is this affected by child age? Moreover, if children with histories of OM do show developmental deficits, can these be shown to be a direct result of CHL or are they the result of coexisting factors such as impoverished or unstimulating developmental and learning environments in which children with middle ear disease often live? Studies in this area are usually of one or more of the following types:

1. Retrospective designs in which the child's history of otitis is taken from medical records or parent interview and early CHL history is deduced indirectly from this. Difficulties with this design type have been highlighted in the classic critical paper by Ventry (1980). These include independent variable isolation and definition difficulties as discussed above, and failure to assess actual degree, configuration and duration of hearing loss directly.
    
   
2. Comparative experimental vs. control group designs which usually search for deficits in affected children using standardised tests of communicative, cognitive, social or educational functioning. Lewis' (1976) study of Aboriginal schoolchildren is an example of this design.
    
   
3. Deductive accounts relating likely CHL levels to effects on the child's acoustic perception and auditory development. Studies by Dobie and Berlin (1979) and Downs (1988) are examples of these and will be discussed below. Perhaps the best example, however, is the work of Eimas and colleagues (see Clarkson et al., 1989) which has demonstrated differences in five-year-olds' abilities to discriminate voice onset time (the bath/path distinction) when they have early-childhood histories of recurrent OM. Recent studies have also demonstrated significantly reduced binaural masking level differences (MLDS) in children with histories of recurrent OME, suggesting that such children may experience difficulties in binaural auditory processing and in detecting and attending to signals in noisy environments (Hall & Derlacki, 1986; Moore et al., 1991; Pillsbury et al., 1991).
    
   
4. Neurophysiological studies Katz (1978) argued that auditory deprivation caused by intermittent CHL may lead to anatomical, physiological and possibly functional changes or developmental delay at the level of the brainstem as well as higher order auditory centres such as speech processing centres and those mediating sensory and motor coordination. This possibility has been tested in animal models where CHL has been artificially induced and possible effects of the auditory deprivation on auditory brainstem tissue development examined. Webster (1979, 1988) demonstrated atrophy in the ventral cochlea nucleus of the auditory pathway following induced CHL in neonate mice, and Moore et al. (1989) reported effects on the cochlear nucleus and projections to the inferior colliculus in the guinea pig.
    
   
5. In children, numbers of electrophysiological studies have examined the effects of recurrent childhood CHL on auditory brainstem responses (ABRs). A common finding in children with early OM histories but with normal hearing at the time of testing is that interpeak wave latencies (I-111 and I-V) are increased, further suggesting an abnormal auditory brainstem response and likely abnormal functioning at lower levels of the ascending auditory pathway (e.g. Folsom et al., 1983; Gunnarson & Finitzo, 1991).
    
   
6. Consequently, Pillsbury et al. (1991) have argued that both reduced MLDs and abnormal ABR wave latencies found in children with histories of recurrent OME may be related to findings of abnormal auditory brainstem development, such as those demonstrated histologically in animal models.
    
   
7. Prospective studies are the best since they avoid methodological difficulties associated with retrospective designs by following children's OM patterns, hearing levels and developmental milestones directly from infancy through early childhood. The studies are not deficit based and are able to assess children's developing skills directly using criterion- referenced or normative tests. Friel-Patti and Finitzo (1990), for example, reported that both receptive and expressive language measures at 12, 18 and 24 months were negatively correlated with average hearing levels from 6 to 12 months in a prospective study; this recent study substantiated previous prospective studies by the same authors (Finitzo-Heiber & Friel- Patti, 1985; Friel-Patti et al., 1986). On the other hand, prospective studies by Roberts et al. have not demonstrated clear relationships between otitis media bouts (OME) in the first three years of life and later language development (Roberts et al., 1988, 1991). These apparently conflicting findings highlight two important possibilities. First, although correlation between OME and elevated hearing levels has been demonstrated (Fria et al., 1985; Friel-Patti & Finitzo, 1990), any effect of OM on child development is likely to occur as a result of OM associated hearing loss, not merely the presence of middle ear disease itself. That is, studies which relate OM history only (and not directly measured hearing levels) to child development (e.g. Roberts et al., 1988, 1991; Teele et al., 1984) are less likely to be successful than those which record the actual 'dose' of hearing loss in the developing child's history by measuring hearing acuity and duration of CHL bouts directly, rather than inferring these from OM histories (e.g. Friel-Patti & Finitzo, 1990). Furthermore, no studies have tested the important suggestion that possible relationships between middle ear disease, CHL and child development may vary with child age, so that the impact of OM-induced CHL may be different at different child ages (Friel-Patti & Finitzo, 1990; Teele et al., 1984) and likely to be greatest in youngest infants.

Nevertheless, despite the controversies concerning methodological difficulties, research in the late eighties has led to more general agreement that CHL resulting from repeated bouts of, or persistent OM in early childhood can have long-term and pervasive effects on children's early auditory, communication and social development and later academic achievement (see Downs, 1985; Haggard & Hughes, 1991; Hasenstab, 1987; Paradise, 1988; Roberts et al., 1991). A range of developmental effects have been associated with CHL and chronic childhood OM in the large body of literature on this topic, and the following provides a brief summary only of common or consistent findings:

1. Central auditory processing deficits and auditory perceptual problems in, for example, digit span tests (Katz, 1978; Kessler & Randolph, 1979), masking level differences and the detection of signals in noise including detection of speech in the classroom and the perception of single words in sentence contexts (Downs, 1988; Jerger et al., 1983; Moore et al., 1991; Pillsbury et al., 1991).
    
   
2. Language learning delay or problems such as comprehension and production aspects of the phonologic system (e.g. Chalmers et al., 1989; Clarkson et al., 1989; de Marco & Givens, 1989; Friel-Patti & Finitzo, 1990; Needleman, 1977; Teele et al., 1983).
    
   
3. Auditory language deficits, as measured, say, by the sound blending test of the Illinois Test of Psycholinguistic Abilities (Zinkus et al., 1978).
    
   
4. Adverse effects on verbal intelligence but not on non- verbal intelligence (e.g. Chalmers et al., 1989; Teele et al., 1990; Zinkus et al., 1978)
    
   
5. Behavioural difficulties, including activity levels, attention span and attention deficit disorder (Adesman et al., 1990; Feagans et al., 1987), distractability, aggressive and disruptive behaviours (e.g. Chalmers et al., 1989; Zinkus et al., 1978)

Effects Of CHL On Development Of Indigenous Children

• The special case of Aboriginal children
• The significance of fluctuating conductive hearing loss in early infancy

There are few studies of developmental or educational effects of OM-induced CHL on children from indigenous populations. It may be predicted, however, that the effects in these populations are not different in kind but greater in magnitude than those described in studies cited above for a number of reasons. These include the probable greater severity and overall duration of their CHL which may commence in early infancy and include frequent bouts of suppurating OM (whereas studies cited above usually consider only bouts of OME in preschool years). Further, many indigenous children suffer CHL in a context of extreme socioeconomic and educational disadvantage and even oppression and, in the case of Australian Aborigines, they may attend bilingual/bicultural schools in which the effects of their CHL history are likely to be exacerbated in classrooms which use English as a foreign language and in which language is used differently in teaching and learning from the way it is used in the child's home culture (see, for example, Harris, 1990).

In one of the few aboriginal studies available, Kaplan et al. (1973) followed a cohort of 489 Alaskan Eskimo children for the first ten years of life, and reported that children with histories of otitis media and CHL in the first two years of life were significantly delayed in verbal ability and educational achievement including reading, mathematics and language skills. In contrast, Fishler et al. (1985) were able to find no significant differences in language performance between two groups of six to eight year-old Apache Indian children with contrasting childhood histories of otitis media since birth.

In Australian Aboriginal children, an anecdotal report by Armstrong (1975) describes Aboriginal students with CHL in remote Central Australian classrooms as introverted, quiet, temperamental, unresponsive to questions, poor attenders, low achievers and frequently displaying speech difficulties. There is only one report in the literature of a formal investigation of the effects of long-term CHL on Aboriginal children's development. Lewis (1976) compared 14 Aboriginal children with two control groups who had normal middle ear function, one Aboriginal and one European. Unfortunately, this study was retrospective and did not measure children's hearing losses directly, but inferred them from information derived from four years previous to the study; no information was available concerning the subjects' real hearing levels during their early developmental years. Nevertheless, Lewis concluded that the Aboriginal group with OM history (and, presumably, CHL) performed more poorly than both control groups on auditory and verbal tasks, including the Wepman Auditory Discrimination Test, a phonetic synthesis task, and the Enticknap Picture Vocabulary Test.

The special case of Aboriginal children

It has already been argued that the developmental and educational effects of early childhood OM may be greater for Aboriginal children for a number of reasons.

First, as argued above, any auditory and language difficulties which these children have with their first language are likely to be exacerbated when they attend school in a bicultural/bilingual classroom. Second, Aboriginal children's CHL seems to be of greater overall severity and duration and has earlier onset than in those non-Aboriginal groups which have been reported in most of the literature concerning otitis media effects on children. Studies of the effects of OM on child development have been mostly done in the US with non-Aboriginal "otitis-prone" children almost always children who have had three or more bouts of otitis media with effusion (OME) per year in early childhood or, as with Roberts et al. (1988) and Teele et al., (1984), child samples with a wide range of number of days with OME in their early years and normal middle ear function at other times. In contrast, Aboriginal children seem to suffer their first bout of OM very early in life (Dugdale et al., 1978), with early OME leading to perforations of the tympanic membrane frequently before twelve months (Douglas & Powers, 1989; Rebgetz et al., 1989). In such children, middle ears may not return to normal until adolescence or even later (McCafferty at al., 1985). Indeed, in a prospective study of Aboriginal infants from birth which we have recently commenced at the Menzies School and which will be described in this seminar (Boswell, this seminar), a number of infants in the small sample have OME within the first weeks or even days of life, and, in at least one case, perforations healing to OME and subsequent reperforation within the first two months of life; initial ABR assessment of these children also suggests that they may be suffering hearing losses between 20 to 55 dB at this early age too. While mean hearing levels associated with OME are close to 22 DBHL (Fria et al., 1985; Kokko, 1974), mean losses associated with perforated ear drums may be as high as 4O dB according to our study.

Thus, Aboriginal infants may suffer hearing loss from very early infancy; hearing levels may not return to normal before adulthood since the disease seems to persist with poor treatment, and it is also likely to be fluctuating as the ear state changes between wet or dry perforations and OME. The possible hearing fluctuations may add further to difficulties in auditory skills development because the auditory system does not have a consistent input during its early developmental period (Downs, 1988).

The significance of fluctuating conductive hearing loss in early infancy

It is well known that the effects of sensorineural deafness upon language development are greatest when the deafness occurs in the prelinguistic years while the auditory and cognitive systems are most actively establishing early skills. Evidence that mild to moderate conductive losses may affect auditory brainstem and auditory processing development is more recent, however.

In recent decades, it has been established the cochlea is fully developed by 20 weeks gestation (Elliott & Elliott, 1964), and that the neonate already has a range of auditory skills and capabilities. For example, numerous studies have shown that neonates show auditory preference for stimuli in the speech range of frequencies, and that they selectively attend to female (especially their own mothers') voices (DeCasper & Fifer, 1980). Further, a range of studies by Eimas has shown that, for example, one-month-olds can make categorical distinctions of voice onset time (VOT) and can distinguish /pa/-/ba/ (see Eimas, 1972, 1975). The infant learns to ascribe semantic meaning to such distinctions later in the course of language development. Eimas (1975) has hypothesised that the auditory system can make such categorical distinctions at or shortly after birth, but that they require stimulation, or auditory experience for them to develop. In this context, the finding by Clarkson et al. (1989) that children with histories of early OM show reduced abilities to discriminate VOT are of particular interest, and this may be of special relevance to the Aboriginal infant with fluctuating CHL.

Conclusion

In conclusion, we are asserting that, because Aboriginal CHL is established in early infancy, because it is greater both in duration and severity than in other studied groups, and because it occurs in disadvantaged, bilingual developmental and educational contexts, current inconsistent treatment and educational management strategies for affected school-aged children are too little, too late. Rather, in order to avoid likely developmental and educational sequelae, OME and CSOM in Aboriginal babies under twelve months ought to be considered a paediatric emergency which warrants aggressive treatment and treatment evaluation strategies at their first appearance.

Figures

 

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