Definitions and causes of Language Impairment

Children with Language Impairment (LI) comprise a very heterogeneous group, whose main shared characteristic is the existence of language difficulties despite otherwise typical development (Kohnert

& Ebert, 2016). When referring to language, it is important to make a distinction between receptive ability, i.e. the process of following and interpreting linguistic information and expressive ability, which refers to the “production of vocal, gestural or verbal signals” (DSM 5, 2013). Prevalence of LI has been estimated to be around 6-8% as regards kindergarten children.

According to DSM-5 a language disorder is characterised by:

- Persistent difficulties in the acquisition and linguistic use across modalities that include reduced vocabulary, limited sentence structure and impairments in discourse

- Abilities that are considerably below those expected by age resulting in functional limitations in effective communication, social participation, and school achievement

- Onset of symptoms should be at the beginning of the early developmental period

- Difficulties are not attributed to hearing or sensory issues, motor dysfunction or neurological conditions

Furthermore, according to the traditionally mentioned criteria mentioned by Leonard (2000), specific language impairment is characterised by:

- Language test scores of -1.25 standard deviations or lower - Nonverbal IQ performance of 85 or higher

- No recent episodes of otitis media with effusion - No structural oral anomalies

The differential diagnosis of Language Impairment or Language Disorder should be based on the following criteria. In general, LI should be differentiated from:

- normal developmental variations due to dialectal, cultural, or other social background - hearing, sensory or motor impairments

18 - intellectual disability

-neurological disorders

-language regression due to autism or other conditions, such as Landau-Kleffner syndrome (DSM-5, 2013).

Furthermore, it is important to mention that recently, especially in the UK, there is increasing use of the term Developmental Language Disorder (DLD) instead of the previously used term Specific Language Impairment, which has been thought to exclude children from access to services and, thus, to no longer be clinically pertinent. DLD characterises serious and persisting language difficulties that affect everyday functioning and are not associated with “any clear biomedical aetiology” (Bishop, Snowling, Thompson, Greenhalgh, Adams, et al, 2017). The term DLD encompasses most of the characteristics mentioned in the DMS-5 and is compatible with said criteria. One area which is slightly different is the replacement of the traditional exclusionary criteria mentioned above with a

combination of differentiating conditions, risk factors and co-occurring conditions. As regards the lack of traditional exclusionary criteria a point of interest is the inclusion of the possibility of a child presenting with DLD in the presence of low nonverbal abilities. The exclusion of the discrepancy criterion between verbal and non-verbal abilities will be analysed later when considering non-verbal tasks (chapter 1.7).

In this study, as mentioned earlier, the term LI will be used interchangeably with the terms language disorder, language difficulty, primary language impairment and DLD.

Language Impairment is considered as a highly genetic condition. Evidence stems from studies involving twins (Bishop, 2002). For instance, despite some variations regarding the severity of the LI in monozygotic twins, environmental factors have been, generally, found to play a relatively

unimportant role in “causing” LI, as opposed to genetic factors (Bishop, 2006). More specifically, reduced performance on nonword repetition tasks has been found to be “highly heritable” (Bishop, 2002). In addition, further studies have contributed to the identification of the FOXP2 gene, which is supposed to regulate the activity of other genes that are responsible for the development of speech and language. In that sense, LI is not clearly attributed to the mutation of a specific gene but rather on a combination of genetic and environmental risk factors (Fisher, 2005). Finally, LI is affected by gender, with boys presenting with LI more than twice as often than girls (Leonard, 2000).

19 1.2.2 Developmental course and characteristics of LI

In brief, the course of LI may initially manifest as the absence of use of a variety of words and word combinations (at around age 2), later as the slow acquisition of grammar rules (during preschool years), and during the school years as less fluent discourse and narrative, comprehension issues, as well as limited vocabulary production and higher probability of reading and writing difficulties (specific learning disorders); (Scott & Windsor, 2000). In sum, some further characteristics of LI are limited phonological processing and phonological discrimination skills, reduced variation of

vocabulary, word finding errors, increased articulation errors, difficulty acquiring verbs, grammatical suffixes, and prepositions, as well as lack of “overgeneralisation errors”, reduced metalinguistic awareness and difficulty understanding passive forms (Chiat, 2001; Leonard, 2000; Marshall & Van der Lely, 2012).

These deficits may present all simultaneously but, more frequently, language impairment manifests itself through combinations of one or two of these symptoms. There have been several proposed classifications of SLI depending on the types of presented characteristics. One common classification refers to symptoms affecting the different linguistic domains, i.e., phonology, semantics,

morphosyntax and pragmatics. Other researchers prefer to differentiate deficits in semantics and pragmatics from errors in phonology and morphosyntax (Leonard, 2000).

As regards the “semantic-pragmatic” category, this type of LI has been associated with word-finding difficulties, restricted understanding of metaphorical language and deficient use of conversational context (Conti-Ramsden, Crutschley & Botting, 1997). Caution is needed, however, regarding this classification as some of its characteristics may, also, be present in autism spectrum disorder and, therefore, such children should be excluded from LI studies. Furthermore, where “pure” semantic difficulties are concerned, reduced vocabulary, that is often expressed through the use of “all-purpose-verbs”, is a characteristic feature (Kambanaros, Grohmann & Theodorou, 2010). The frequently noted word-finding difficulties are expressed in the form of errors of semantic association (e.g., foot instead of shoe). These problematic semantic associations have been explored both using offline as well as online tasks of word processing, such as event-related brain potentials (ERPs). During a study

involving the latter methodology, Haebig, Leonard, Usler, Deevy & Weber (2018) found that during a lexical judgment tasks LI-children exhibited a less mature profile of semantic “post-lexical”

reconstruction and integration than their typically developing peers.

When considering the word-retrieval process presented earlier, possible errors may result from a breakdown at the initial phase where the lemma is accessed (lexical-semantic error), as well as the second phonological (lexeme) phase (phonological errors). Lexical errors are affected by the imageability (abstraction) of a word and phonological ones by the frequency of a given word.

Furthermore, there is evidence that the ability to spot transitional sound probabilities in order to be

20 able to make associations between words and referents, through implicit, statistical learning is

compromised in children with LI, not only for linguistic (i.e., sounds) but, also for non-linguistic stimuli (i.e., tone sequences); (Evans, Saffran, & Robe-Torres, 2009). The specific type of difficulty is analysed in more depth in connection to the theoretical underpinnings of LI.

Where the phonological-morphosyntactic “sub-category” is concerned, there is general consensus, as well as a substantial body of research, supporting that the existence of morphosyntactic deficits, which often is accompanied by phonological errors, constitute the most prevalent type of LI to the extent that is often referred to as “typical SLI” (Bishop, 2004).

Due to the significance of phonological deficits for the present study, it is important to present some additional information on this subject. “Phonological deficits” are a part of what is known as speech sound disorders (SSD). Speech sound disorders might be divided in functional and organic disorders.

Functional disorders are of unknown origin and may include articulation or phonological aspects.

Organic speech sound disorders might be developmental or acquired and can be divided in: a) motor-neurological disorders of execution (dysarthria) or planning (dyspraxia), b) structural disorders (orofacial anomalies or cleft-palate) or related to trauma, and c) sensory or perceptual disorders (hearing impairment); (American Speech-Language-Hearing Association, 2021).

Without considering their aetiology, Dodd (2005) proposed a classification system based on the types of SSD errors that has been useful clinically for diagnostic profiling and is especially relevant for our project. SSD are classified into articulation disorders, delayed phonological acquisition, consistent deviant disorders, inconsistent deviant disorders, and other (including dysfluency, dysarthria, and apraxia of speech). It should be mentioned that developmental apraxia or dyspraxia is a distinct type of SSD with a long-term effect on academic skills (Lewis, Free-bairn, Hansen, Iyengar, & Taylor, 2004).

Lastly, Lewis et al. (2011) proposed an interesting classification of SSD based on the severity level and type of performance on a PCCR task. More specifically, they compared the performance of 237 children with SSD and their TD siblings in an attempt to come up with different endophenotypes of SSD. Interestingly, they observed that the highest recorded comorbidity with Language Impairment involved the category of children with developmental dyspraxia (97%), and moderate speech sound disorders (55%). On the other hand, children with milder speech sound disorders had much lower percentages of LI. As regards the observed endophenotypes, phonological memory, phonological awareness and vocabulary were associated with the severity of SSD, the existence of comorbid LI and reading difficulties, as well as the categorisation into SSD, SSD and LI, and developmental dyspraxia.

21 For information (Lewis et al, 2011), the reported comorbidity of LI and “speech or phonological delay” has been estimated to be around 11-15% regarding 6-year-old children and between 40 % -60%

regarding preschoolers, which is the age group of interest for this project.

Going back to the characteristics of “typical” SLI acquisition, the following examples may be presented. In English and Germanic languages, it appears that regularisations (i.e., the morphological substitution of an irregular form through a regular one) in SLI children, are much more strongly affected by frequency effects, compared to typically developing children (Van der Lely, Bishop, Bright, James. & Bishop, 2000). In addition, there is evidence that while typically developing children often prefer using regular over irregular past tense forms, SLI children do not. Nonetheless, even when considering SLI children with morphological issues, one should take into account that this is a very heterogeneous groups as not all SLI children present with the patterns presented above; for instance, some present with specific difficulties at a primarily syntactic level, such as the comprehension and production of “Wh-questions” and relative clauses. This has led some researchers to refer to a distinct sub-classification of LI-children, the so-called “G-SLI” (Grammatical SLI); (Van de Lely, Bishop, Bright, James. & Bishop, 2000). This less researched area of LI, along with an analysis of the theoretical background explaining most said characteristics follows in the next section.

It is worth mentioning that the morphosyntactic errors which are play such a crucial role in language impairment are evident across languages. Such errors include clausal relationships and word order, as well as the use of grammatical morphemes, such as tense, gender, number, case, and person (Orgassa, 2009). Said morphemes, including copula, auxiliaries and determiners are either less frequently used or substituted. The extent of these grammatical omissions or substitutions varies across languages. For instance, in languages where pronouns are generally omitted (null-subject languages), such as many Asian or Romance languages, substitution errors are rather common. On the other hand, in non-null-subject languages, such as the Germanic languages, omissions of finiteness, such as verb and tense agreement, are frequent. These different language-specific errors have prompted different theoretical interpretations, which will not be analysed in this chapter. The reader is referred to Leonard (2000), Blom & Baayen (2001) and Rice & Wexler (1996) for a detailed theoretical review. A more detailed reference to LI profiles of children in German follows in section 1.3.

Lastly, according to the classifications published during the Delphi consortium consensus study (Bishop Snowling, Thompson, Greenhalgh, Adams, et al., 2017), DLD is further characterised by deficits in verbal memory and learning, which is expressed by difficulties retaining sequences of sounds, associating words with meanings, or learning statistical patterns; these deficits are not better explained by deficits in hearing or general auditory processing. Furthermore, there is, also, evidence that children with LI may exhibit “subtle, subclinical inefficiencies” (Ebert & Kohnert 2016) in

22 processing nonverbal information, in areas such as working memory, processing speed and attention (Leonard, Weismer, Miller, Francis, Tomblin & Kail, 2007; Ebert & Kohnert, 2011).

Overall, it should be mentioned that most of these distinctions been supported by biological,

psycholinguistic, neuroscientific, and genetic data. Marinis & Van der Lely (2007) mention that there are indications that different observed LI- “phenotypes” (lexical S-LI, pragmatic difficulties,

grammatical S-LI etc.) are probably the expression of different genetic variants (Newbury & Monaco, 2010). For instance, different loci on distinct chromosomes have been associated with deficits in different linguistic domains, such as phonological memory, and expressive language (Bishop, Snowling, Thompson, Greenhalgh, Adams et al., 2017).

1.2.3 Theoretical accounts of LI

From a theoretical perspective, LI is either considered as a deficit of a cognitive mechanism

specialised in production of linguistic representations (domain-specific approach) or as the result of a more generalised cognitive weakness (domain-general account). The domain specific approaches are grounded on the generative theory (Chomsky, 1965) and have, therefore, employed concepts from it.

The main idea here is quite specific: the “innate” grammatical system is flawed, leading to LI.

However, more than one “representational” sub-theories have emerged, which differ on whether their interpretation “covers” a specific grammar sub-system or provides an explanation involving a more complete range of morphological impairments.

Within these different approaches exist further theoretical sub-distinctions (Stavrakaki S., in Pontikas G.; 2016). For example, even within representational accounts there is no consensus as to what the fundamental nature of the observed morphological difficulties across languages is. For instance, Clahsen (1991) argues for an agreement deficit based on German data –further explained in the next chapter-whereas Rice & Wexler (1996) maintain that there is a tense deficit based on English data.

Based on Rice’s theory, which is termed Extended Optional Infinitive Account, the lack of obligatory tense marking (finiteness), is the characteristic of an -early- developmental stage of typical language development, which in SLI, is ‘extended’.

As regards the agreement deficit approach (Clahsen, 1991), it is applied in Germanic languages but may not account for LI in non-null-subject languages, where agreement deficits are much rarer. An additional, more recent, “representational” approach has been proposed by Van der Lely (2000), which aimed to account for the errors of the previously mentioned “Grammatical SLI” children, which is a category of children with specific, syntactic errors. Based on her theory a deficit of the Computational Grammatical Complexity, i.e., the computational system responsible for grammatical operations, is responsible for problems with structure-dependent relationships, observed in marking tense and

23 agreement, case assignment, as well as “movement operations”. Furthermore, this approach has been further applied to explain other frequently observed morphological behaviours of LI children, such as omission of plural or third person -s. Based on the Computational Grammatical Complexity theory, errors such as omissions are the result of an inability to verify the grammaticality of a given word within a sentence, in the presence of adequate memory skills (Van der Lely & Christian, 2000, Gopnik, 1990). Further examples include the omission of plural-s within compound words, as well as the ability to interpret “movement operations” during wh-questions, whereby the question word needs to be placed at the beginning of the word. With regards to such tasks, Marinis & Van der Lely (2007) found that G-SLI children did not rely on syntactic information but rather use semantic data to analyse and interpret those types of questions.

Finally, an approach that may be classified as a ‘representational’ account, has been proposed by Ullman (2004). The so-called Declarative-Procedural model emphasises the application of

grammatical knowledge through a dual system: declarative knowledge, which governs everything that is learned in an automated, subconscious way, such as lexical information, and procedural knowledge, which is involved in conscious and active learning, such as the rule-governed, implicit, grammatical morphology. According to this theory, LI-children’s procedural memory is deficient, whereas declarative memory remains relatively intact. This explains the fact that learning the rules of

morphology, such as in agreement inflection, is highly problematic, while at the same time, it accounts for the existence of a few instances of compensated, ‘correct’ grammatical structures that are based on declarative memory.

Research evidence supporting that procedural, implicit learning is, indeed, problematic in children with LI stems from studies, whereby LI-children presented with slower reaction times compared to controls during a serial reaction time task (Tomblin, Mainela-Arnold & Zhang, 2007), as well as research using classical artificial grammar learning tasks showing that LI children were less able to implicitly learn the rules of a novel grammar structure based on paradigms from that grammar (Alt, Plante & Creseure, 2006; Evans, Saffran, & Robe-Torres, 2009). This ability has been further tested through alternative measures, such as statistical testing, where individuals are required to track patterns during transmission of different stimuli, such as syllables and tones, in order to extract regularities; the fundamental assumption of these studies is that, typically, infants and adults are easily able to detect familiar vs novel patterns of presented stimuli. This ability has been linked to being able to identify the word boundaries when listening to streams of sounds and, thus, learn new words.

Evans, Saffran, & Robe-Torres (2009), set out to explore how LI children perform on such tasks of implicit learning, and whether their performance depended on exposure and type of stimulus

(linguistic or not). Their conclusions were that LI’s children “computational” ability to track statistical regularities in order to identify word boundaries is less developed than in typically developing

children, that it depends on the time of exposure to the stimuli, and that this difficulty does not only

24 involve linguistic (i.e., speech) but, also, non-linguistic stimuli, such as tones. Overall, they conclude that the observed deficits may be explained by an adapted version of the representational account presented by Ullman that would include other aspects of implicit learning, such as word learning.

On the other hand, processing accounts vary from those proposing general processing capacity deficits to be the main cause of SLI (Leonard, 2000) to the ones suggesting that limitations of specific

subsystems, such as phonological memory, are responsible for the observed deficiencies (Gathercole

& Baddeley, 1990).

The Morphological Richness account and the Surface Account are two closely related processing theories both postulated by Leonard (2000). The main idea of both accounts is that LI is caused by difficulty to perceive specific morphological characteristics that are more transparent in certain languages compared to others, as indicated by many cross-linguistic studies. More specifically, the Surface Account links LI deficits with a shortage of the auditory processing system to perceive less salient information, especially in languages with less clear contrasts between strong and weak surface characteristics, such as syllabicity, duration of syllables/ morphemes etc. This leads to weaker

morphological representations, especially in languages with less salient grammatical characteristics e.g., English compared to Spanish. In the same vein, based on the Morphological Richness Account, languages with richer inflectional systems provide opportunities for more consistent input to different morphological structures, thus, facilitating the creation of correct grammatical representations.

With regards to the domain-general (processing) accounts, they have been supported by studies evidencing that LI children demonstrated slower response times during linguistic and non-linguistic tasks (Gillam, Gillam, Fargo, Olszewski, Segura et al., 2017; Leonard, Weismer, Miller, Francis, Tomblin et al, 2007). Within this context the required processing time is synonymous to processing capacity; also, each presented task might involve several stages that contribute collectively to the

With regards to the domain-general (processing) accounts, they have been supported by studies evidencing that LI children demonstrated slower response times during linguistic and non-linguistic tasks (Gillam, Gillam, Fargo, Olszewski, Segura et al., 2017; Leonard, Weismer, Miller, Francis, Tomblin et al, 2007). Within this context the required processing time is synonymous to processing capacity; also, each presented task might involve several stages that contribute collectively to the