Elsevier

Journal of Communication Disorders

Volume 44, Issue 6, November–December 2011, Pages 745-763
Journal of Communication Disorders

Behavioral profiles associated with auditory processing disorder and specific language impairment

https://doi.org/10.1016/j.jcomdis.2011.04.001Get rights and content

Abstract

Purpose

To describe and compare behavioral profiles associated with auditory processing disorder (APD) and specific language impairment (SLI) in school-age children.

Method

The participants in this cross-sectional observational study were 64 children (mean age 10.1 years) recruited through clinician referrals. Thirty-five participants had a clinical diagnosis of APD and 29 were receiving services for language impairment. Participants completed 18 behavioral measures of spoken language, auditory processing, reading, memory, and motor speed. Responses were used to classify children as affected/not affected with APD, and affected/not affected with SLI. Comparisons were made between children with and without an APD diagnosis, and between children assigned to the APD/not APD and SLI/not SLI groups. Agreement between clinical status and test-based classifications is also reported.

Results

There were no group mean differences between children with and without a clinical diagnosis of APD. Group mean differences on Cube Design and reading fluency were observed for children classified as APD/not APD; and group mean differences on nonword repetition, spatial working memory, and two auditory processing tests were observed for children classified as SLI/not SLI.

Conclusions

The behavioral profiles of children with APD and SLI were very similar. Although group mean differences were found, they were difficult to interpret in terms of current theories.

Learning outcomes: The reader will be able to: (1) describe similarities and differences found between children with SLI and children with APD and (2) discuss assessment problems posed by overlapping behavioral characteristics of SLI and APD.

Highlights

► No differences in language, reading, memory found between children with and without a clinical APD diagnosis. ► Children with and without test-based APD diagnosis differ on cube design and reading fluency. ► Children with and without test-based SLI diagnosis differ on nonword repetition, spatial working memory, and two auditory processing tests.

Introduction

Auditory processing disorder (APD) and specific language impairment (SLI) are developmental communication disorders that clinicians and researchers have investigated for decades (Jerger, 2009, Leonard, 1998). Auditory processing disorder (APD) is defined as “difficulties in the processing of auditory information in the central nervous system” (American Speech-Language-Hearing Association [ASHA], 2005, p. 1). The diagnosis is given when functional listening difficulties are observed in the presence of normal peripheral hearing and the child demonstrates deficits in one or more auditory skill areas that include discrimination, pattern recognition, temporal integration and ordering, dichotic listening, and the perception of degraded stimuli (ASHA, 2005). Children with APD often have difficulties with reading, spelling, and expressive and receptive language (ASHA, 2005, Dawes et al., 2008, Jerger and Musiek, 2000, Sharma et al., 2009).

Difficulties with reading, spelling, and expressive and receptive language are also observed in children with specific language impairment (SLI; Catts and Kamhi, 2005, Leonard, 1998). A diagnosis of SLI is given to children whose language abilities are not as well developed as those of other children who are the same age, exhibit the same level of nonverbal intelligence, and have similar opportunities for learning. Language deficits may be observed for expressive language only, or for expressive and receptive language. Possible reasons for language delay, including hearing loss, oral-motor dysfunction, cognitive impairment, and social-behavioral disorders, are ruled out in SLI (Leonard, 1998).

One controversy is whether there is truly a “disorder” of auditory processing with underlying etiological unity that is distinct from other learning disabilities (Cacace and McFarland, 1998, Dawes and Bishop, 2009, Moore, 2006). Clinical commentaries in textbooks (Bellis, 2003, Chermak and Musiek, 1997) and consensus statements (ASHA, 2005, Jerger and Musiek, 2000) assume the validity of APD as a construct; however, researchers have noted that individuals with APD often present with language and/or reading deficits similar to those observed in individuals with SLI. Studies by Sharma et al. (2009) and Dawes et al. (2008) have documented language and reading deficits in individuals with a clinical diagnosis of APD or laboratory test performance indicative of APD. In stating that APD “may lead to or be associated with difficulties in higher order language, learning, and communication functions” (p. 2) ASHA's (2005) technical report not only notes that APD and SLI have overlapping symptoms, but also suggests that APD plays a causal role in some language impairments.

There is more consensus about the validity of SLI as a construct; however, the precise nature and etiology of the deficits in SLI remain unresolved (Leonard, 1998). One hypothesis, which continues to be controversial, is that auditory processing deficits play a causal role in SLI (Dawes and Bishop, 2009, Moore, 2006, Rosen, 2003). This hypothesis has been considered for decades (see reviews by Rees, 1973, Rosen, 2003) and there is a large literature investigating it (e.g., Banai and Kraus, 2007, Basu et al., 2009, Bishop and McArthur, 2005, McArthur et al., 2009, Tallal and Piercy, 1973a, Tallal and Piercy, 1973b, Tallal, 2004). Although many individuals with SLI, dyslexia, or more broadly defined language-learning problems have difficulty processing brief, rapidly presented stimuli and/or making frequency discriminations, a substantial proportion of these individuals perform within the normal range on auditory processing tasks (e.g., Banai et al., 2005, Bishop et al., 2005, McArthur and Bishop, 2005). These observations suggest that SLI can be present without auditory processing deficits (Bishop, Carlyon, Deeks, & Bishop, 1999).

Four possible relations between APD and SLI are described below and depicted in Fig. 1.

  • (1)

    SLI and APD are distinct constructs that can be distinguished theoretically and clinically.

  • (2)

    SLI and APD are different labels for the same construct.

  • (3)

    SLI is a subset of APD. Some children with APD have SLI, but all children with SLI have APD.

  • (4)

    APD is a subset of SLI. Some children with SLI have APD, but all children with APD have SLI.

Alternative 1 is often assumed in discussions of APD and its relation to other disorders (e.g., ASHA, 2005); however, it has not been tested directly. Clinically, APD and SLI can be difficult to distinguish (ASHA, 2005, Dawes and Bishop, 2009, Jerger and Musiek, 2000, Moore, 2006), but this observation need not lead us to conclude that the two constructs are isomorphic (Alternative 2). Although investigations of Alternative 3, which start with a sample of individuals with APD, are scarce, Sharma et al. (2009), Dawes et al. (2008), and Ferguson, Hall, Riley, and Moore (2010) have documented language and reading deficits in individuals with APD. Alternative 4 has received the most research attention, frequently motivated by a desire to better understand SLI. As reviewed in the previous section, there is considerable evidence that a substantial proportion of children with SLI have auditory processing deficits (e.g., Banai et al., 2005, Basu et al., 2009, Bishop and McArthur, 2005, Bishop et al., 2005, McArthur and Bishop, 2005, McArthur et al., 2009). The exact nature of those deficits, however, remains unclear, and it is also not clear whether clinicians would consider the children with SLI who have auditory processing deficits to also have APD, because the tasks used by researchers to assess auditory processing are not the same as those used by clinicians to diagnose APD. No study has found an entire sample of children with SLI who all have auditory processing deficits, or an entire sample of children with APD who all have language deficits.

Although the current study does not attempt to distinguish among the four alternatives, it does seek to provide a thorough description of the behavioral profiles of children with APD and children with SLI. This behavioral description is a necessary first step toward determining which of the four alternatives is most accurate. To date, there is little research directly investigating the overlap in symptoms observed among children with APD and children with SLI. We wanted to know whether APD and SLI might be distinguished behaviorally in this sample.

The characteristics of individuals with SLI are fairly well described for a wide range of behaviors that include spoken language comprehension and production, literacy, and memory (Leonard, 1998). Although comparatively little is known about the behavioral characteristics of individuals with APD, clinical profiles may include reading and spelling difficulties, phonological deficits, poorer verbal than performance IQ, and poor vocabulary (Bellis, 2006) – all of which are likely to be observed in children with SLI (Leonard, 1998). For the present study, measures were chosen that would assess these different aspects of language and literacy, as well as auditory processing performance. We attempted to assemble a comprehensive battery that could be completed in a reasonable amount of time. The battery was used to classify children into two groups: those children with and without SLI, and those children with and without APD. These classifications, unlike the clinical classifications with which the children entered the study, were not mutually exclusive. In fact, as shown in Fig. 2, a substantial proportion of children met the criteria for both SLI and APD. These non-mutually exclusive classifications derived from our laboratory testing are hereafter referred to as “test-based” classifications. We recognize that the clinical diagnoses that the children received from practitioners were also based on test scores.

The position stated as alternative (1) in the previous section—SLI and APD are distinct constructs that can be distinguished theoretically and clinically—suggests that the test-based behavioral profiles of children with SLI and children with APD will differ. Specific predictions about how they might differ are stated in the following paragraphs along with the descriptions of the measures that were used. To the extent that alternative (1) is not supported by the data, we would conclude that particular behavioral characteristics may be shared between children with SLI and children with APD. More specifically, if SLI and APD were isomorphic, one would not expect to find group mean differences between children with SLI and APD.

Standardized tests frequently used in research on language disorders were chosen to sample receptive and expressive vocabulary and grammar, to the extent that it is possible to isolate modalities and domains of language. The nonword repetition test, a processing-based language measure, was also included. Poor nonword repetition has been found to be strongly associated with SLI across a number of studies and nonword repetition tasks (Graf Estes, Evans, & Else-Quest, 2007). Given the evidence for language difficulties in children with APD, we might expect that both APD and SLI groups will perform poorly on spoken language measures. However, to the extent that APD affects the comprehension of auditory input, performance on tasks that assess receptive language could be particularly weak in children with APD.

Four tests of auditory processing were chosen to represent temporal processing, frequency and duration discrimination, and dichotic listening, following the minimal battery approach of Jerger and Musiek (2000). The specific tests (described in Section 2) selected were commonly used, commercially available tests that include expected scores for children in the age range of the participants in the present study. Tests with speech and non-speech stimuli were used. One would expect the performance of children with SLI to be better with non-speech stimuli relative to speech stimuli because the language deficits of children with SLI would limit their performance on the latter. Children with APD, if they have problems with all types of auditory input, could be expected to perform at least as poorly with non-speech stimuli as with speech stimuli (Dawes and Bishop, 2009, Moore, 2006). Oral reading fluency was assessed because reading problems are often associated with both APD and SLI (e.g., Catts and Kamhi, 2005, Sharma et al., 2009). A nonverbal IQ test was included, to rule out cognitive impairment in the participants and to provide a measure of general intellectual ability.

Measures of nonverbal and verbal working memory were also included in the test battery. The Competing Language Processing Test (CLPT; Gaulin & Campbell, 1994) is often used to assess verbal working memory in studies of children with SLI (e.g., Karasinski and Ellis Weismer, 2010, Montgomery and Evans, 2009, Thordardottir, 2008). The Spatial Working Memory Test (SWMT; Ellis Weismer, 2008) is a visual span task that was chosen because its structure is parallel to that of the CLPT. Verbal working memory is known to be a weakness for children with SLI (Montgomery, 2003). It may also be a weakness for children with APD, although the evidence regarding APD is equivocal. In their sample of children with diagnosed or suspected APD, 76% of whom also met criteria for LI, Sharma et al. (2009) found that 59% of the entire sample had poor forward digit span scores. The mean backward digit span score for the sample was within 1 SD of the mean. Ferguson et al. (2010) found that children with SLI were significantly poorer on a combined forward and backward digit span score compared to the control group, whereas children with APD did not differ from controls. The evidence is mixed as to whether children with SLI perform poorly on tasks that tap nonverbal working memory (Archibald and Gathercole, 2007, Bavin et al., 2005, Ellis Weismer, 2008, Hoffman and Gillam, 2004). Nonverbal working memory is not expected to be depressed in children with APD.

A test of motor speed was included in the present study because children with SLI often demonstrate motor difficulties (Hill, 2001). There have been no reports of such difficulties in children with APD. A tapping task used by Bishop (2002) was selected because it has been shown to discriminate between children with SLI and controls and is quick and easy to administer. Finally, a parental checklist of attentional behaviors was included because APD and attention deficit/hyperactivity disorder often co-occur and have some common symptoms (Chermak et al., 2002, Dawes and Bishop, 2009, Riccio et al., 1994).

The measures used in this study vary in the extent to which their psychometric properties have been documented. Some are standardized tests that have documented validity and reliability with a limited number of populations. However, their sensitivity and specificity for identifying a disorder may be less well established (Spaulding, Plante, & Farinella, 2006). Other measures are published tests with suggested cutoff scores for different age bands, but without normative data. Still others are experimental measures that have not been used systematically in a normative fashion. Although the purpose of the study was not to critique specific instruments, in Section 4 we consider some implications of the varying extent to which the psychometric properties of the measures we used are well known.

The overall purpose of the present study was to determine whether behavioral profiles associated with APD and SLI could be clearly distinguished in a single sample of children with clinical histories of these disorders, when the children were grouped according to clinical history and according to laboratory testing. The data generated will contribute to better understanding of the constructs of SLI and APD, and how to assess them. The specific goals of the current study were, first, to describe the behavioral profiles of children with APD, and the behavioral profiles of children with SLI; and second, to document similarities and differences between these profiles. We grouped our sample in three ways to address the following three questions.

  • 1.

    Did the test-based behavioral profile of children with a clinical diagnosis of APD differ from the profile of children with language impairment (LI) who were not diagnosed with APD?

  • 2.

    Did measures of spoken language, auditory processing, reading fluency, memory, motor speed, and nonverbal cognitive abilities serve to distinguish children who were classified as having APD (or SLI) from children who were not classified as having APD (or SLI) with our test battery?

  • 3.

    Did the test-based classifications addressed in question 2 agree with the clinical diagnoses with which children entered the study?

Section snippets

Recruitment

Participants were recruited by asking school- and clinic-based speech-language pathologists (SLPs) and clinic-based audiologists to distribute invitation letters to the parents of children who met investigator-provided inclusionary and exclusionary criteria. Participants were also recruited through two private schools serving children with language-related learning disabilities. Brochures about the study were distributed through schools and parent groups. To protect participants’

Results

Our analyses use the available data obtained from 64 children on 18 variables. Summary statistics are presented in Table 1, Table 2, Table 3. Three cases had missing data on a total of three variables: FPT, UNIT Symbolic Memory, and expressive vocabulary. One participant refused to complete the FPT. The expressive vocabulary score for one participant and the UNIT Symbolic Memory subtest score for one other participant were not available due to experimenter error. Because each multivariate test

Group comparisons

We found no statistically significant group mean differences on any of the 18 behavioral variables examined between children who received a diagnosis of APD from an audiologist and children who received services for language impairments but did not have an APD diagnosis. Specifically, the two groups did not differ on tasks that measured auditory processing, grammar and vocabulary, reading fluency, verbal and nonverbal working memory, motor speed, and parent-rated attentional functioning. These

Author note

Carol A. Miller, Department of Communication Sciences and Disorders, The Pennsylvania State University; David A. Wagstaff, HHD Consulting Group, College of Health and Human Development, The Pennsylvania State University.

This research was supported by grant 5 R03 DC007312 from the National Institute on Deafness and Other Communication Disorders. Many thanks to the children and their families who participated, to Amanda Owen, Elina Mainela-Arnold, and Patricia Deevy for their comments on earlier

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