Definition and terminology

2 Theory

2.1 What is developmental language disorder?

2.1.1 Definition and terminology

Child language acquisition is often viewed as a universal and robust developmental process that occurs without the help of explicit instruction, provided there is an adequate level of input. The inner mechanisms driving this development are in large part not yet fully

understood, and there is both evidence and disagreement over the roles of various factors we know to have an effect on language acquisition, such as neurobiological development, input, learning, and socialization (Shatz, 2009). Another dimension to our understanding of child language acquisition is the fact that some children have significant difficulties acquiring their first language without any obvious neurobiological or environmental basis. They have normal hearing, show no evidence of neurological damage, and do not meet the diagnostic criteria for other developmental disorders associated with language impairment, such as autism spectrum disorder (ASD) or mental disability. The most common term applied to these children has been specific language impairment (SLI; e.g. Leonard, 2014a), though the term

developmental language disorder (DLD; e.g. Bishop, 2017) has been recommended as a replacement for SLI. In this paper I will prefer the use of DLD – the reasons for which are stated further down. Earlier terminology has included developmental aphasia, dysphasia, primary language impairment, and more generally, language impairment (Leonard, 2014a).

The prevalence of this type of language difficulty is estimated to be approximately 3% to 7%

of the population depending on diagnostic criteria (Tomblin, Records, Buckwalter & Zhang, 1997; Norbury et al., 2016). In a very practical sense this means that in a school class of thirty-some children, a teacher could expect to meet one or two children with a developmental language disorder. Despite this, DLD is a far lesser-known condition amongst both clinicians and the general public than other developmental disorders such as dyslexia or ASD – the latter having a much lower prevalence than DLD (Kamhi, 2004). Bishop (2017) suggests this is in part a result of inconsistent terminology, definitions and diagnostic criteria. With the aim of yielding a professional consensus on the definition and terminology applied to childhood language disorders, Bishop and colleagues (Bishop, Snowling, Thompson, Greenhalgh & the

3 CATALISE Consortium, 2016; Bishop, Snowling, Thompson, Greenhalgh & the

CATALISE-2 Consortium, 2017) asked a panel of experts to respond to a set of statements on appropriate identification criteria and terminology for children with language disorders

including specific language impairment. Firstly, the panel agreed that reasons for referral to a specialist could be concerns about the speech, language or communicative abilities of the child expressed by caregivers, teachers or healthcare professionals (Bishop et al., 2017), representing a broad view of the clinical picture of a child with DLD. Assessment of these children, according to the panel, should draw from multiple sources including direct observation, interviews with caregivers and standardized, age-appropriate language tests (Bishop et al., 2017). In general, the panel emphasized assessing the functional impact of the language disorder on the child’s daily activities, rather than relying solely on test scores or an arbitrary cut-off to determine whether or not a language disorder is present.

The conclusions of the CATALISE study were not a complete departure from the established practice; however, criteria for SLI often required a certain discrepancy between nonverbal abilities and language abilities, and/or a lower cut-off of at least 85 on a test of nonverbal abilities (Leonard, 2014a). Children could therefore be excluded from the diagnosis if their lower-than-average language abilities were accompanied by a lower-than-average nonverbal IQ (NVIQ) score. Exclusion from a diagnosis can often mean exclusion from treatment, and this is not only unfortunate; it is also not supported by research findings (Norbury et al., 2016). There is no evidence that speech-language therapy is effective only for children with a large discrepancy between language skills and nonverbal abilities, nor is there evidence that children with low-average nonverbal abilities cannot benefit from clinical language

intervention (Cole, Dale & Mills, 1990; Bowyer-Crane, Snowling, Duff & Hulme, 2011).

Citing these and other studies, Bishop et al. (2016, 2017) did not support using NVIQ as an exclusionary criterion for the diagnosis of a developmental language disorder.

Another outcome of the CATALISE study was the recommendation that the term “specific language impairment” be replaced with “developmental language disorder” (Bishop et al., 2016, 2017; Bishop, 2017). The more general term “language disorder” was defined as childhood language problems enduring into the school years and beyond, with “a significant impact on everyday social interactions or educational progress” (Bishop et al., 2017, p. 3-4).

The term DLD should be used, according to the panel, when such a language disorder occurs where there is no known biomedical condition which could explain it in part or fully.

4

Incidentally, a research project based on CATALISE is underway in Norway to determine appropriate terminology in Norwegian (CATALISE Norge, 2019). Until now, Norwegian educators have generally used the terms språkvansker, “language difficulties” or spesifikke språkvansker (SSV), “specific language difficulties,” when referring to these children. This study will use the term DLD when referring to children with an unexplained delay or disorder in acquiring their first language, in support of the revised terminology and criteria proposed by Bishop et al. (2016, 2017). Nevertheless, in some cases SLI or simply “language

impairment” will be used interchangeably, acknowledging that much research up until recently has employed these terms when referring to children with DLD.

The question remains, however, as to whether the condition of DLD truly represents a separate category: a diagnosis for which we can eventually hope to identify the exact neurobiological basis. Although it seems highly likely that there is a genetic component to DLD, based on evidence from twin studies (Tomblin & Buckwalter, 1998) and molecular genetics (SLI Consortium, 2004; Newbury & Monaco, 2008), researchers have as yet not been able to determine a universal “cut-off” that would distinguish children with DLD from children at the low end of normal variation in language ability (Bishop, 2017; Leonard, 2014b). To the contrary, the available evidence seems to imply that children with DLD in fact

“fall on the weak end of a language ability continuum” (Leonard, 2014b, p. 45). This

statement notwithstanding, the debate continues in speech and language research fields as to whether a developmental language disorder mainly represents a quantitative delay compared to the normal developmental pattern, or whether the language development of children with DLD is qualitatively different – deviant from normal development – in ways that could guide diagnosis and treatment (Baird, 2008).

The current study will investigate both quantitative and qualitative differences between Norwegian-speaking children with DLD and typically developing children, but is too limited to attempt to respond to this question in a general sense. However, regardless of whether DLD is better characterized as language delay or as an abnormal path of language development, the fact remains that these children can experience difficulties which can follow them throughout their school years and beyond, impacting quality of life. This is reason enough to continue conducting research which could help us improve guidelines for assessment and treatment of this condition. DLD is most often diagnosed during the preschool years, and despite the relative success of language intervention, many children may never achieve age-appropriate

5 language skills (Leonard, 2014a). Children with DLD, particularly those with more severe difficulties, will often experience long-lasting problems with communication which continue to affect them into their adolescent and adult lives. Children whose language difficulties persist into their school years are more vulnerable to mental health problems in adolescence and adulthood (Snowling, Bishop, Stothard, Chipcase & Kaplan, 2006; Conti-Ramsden, Mok, Pickles & Durkin, 2013). The demands placed on oral and written communication are only increasing in our current information-based society, and as such we could expect childhood language and communication difficulties to impact the well-being and future success of these children to an even greater extent than previously (Tomblin, 2019). It is therefore imperative to gain more accurate knowledge of the nature and causes of DLD, with the hope that this should lead to better practices in individual treatment as well as in school settings.

2.1.2 Classification and subtypes of developmental language