Investigating sign language development, delay and disorder in deaf children
Chloë Marshall & Gary Morgan
Chloë Marshall
Department of Psychology and Human Development
Institute of Education
20 Bedford Way, London WC1H 0AL, UK
Gary Morgan
Deafness, Cognition & Language Research centre (DCAL)
City University London
Northampton Sq.
London, EC1V 0HB, UK
g.morgan@city.ac.uk
Acknowledgements
This research was supported by the Economic and Social Research Council: Grants 620-286001,620-28-6002 (Deafness, Cognition and Language Research Centre) to Gary Morgan,
and by a Leverhulme Early Career Fellowship awarded to Chloë Marshall.
Running Head: Sign language developmental disorders
1
Abstract
Around 7% of hearing children have a language learning disorder. In this chapter we explore
whether a language disorder can also occur in deaf children who sign. One of the most
researched areas in deaf children’s development is their acquisition of language. Native
signers achieve predictable milestones during language development but represent a small
group within the deaf child population. Many studies have found serious and long-lasting
effects of early language deprivation on linguistic and communicative competence in deaf
children with hearing parents. However there has been little attempt to tease apart whether
these problems are caused by delayed exposure, a language learning disorder or both. Indeed,
the distinction between delay and disorder is a very difficult one to make and is tied to how
we assess children’s signing skills.
This chapter reviews what we understand about sign language developmental
disorders. As with the study of language impairment in hearing children, much of the devil is
in the detail. Establishing a research methodology which can reliably separate out effects of
natural variation, delay and disorder is all about who is in the research team and what tools
are available for assessment. Notwithstanding these challenges, it is important that a deaf
child’s language assessment can pinpoint what aspects of language need to be addressed so
that any intervention is evidence based. Our studies indicate that the picture is a complex one,
with both variation across children and differences between language disorder in the deaf and
hearing populations.
Key words: deafness, sign language, language disorder, specific language impairment,
assessment
2
Many species communicate, but only humans have language. Language is universal across all
cultures, and it is almost impossible to imagine how activities so central to our lives such as
maintaining relationships, thinking and instructing others could happen without it. For
example, current ideas about how children develop theory of mind stress the vital
contribution of their language and communications skills (Pyers & Senghas, 2009; Meristo,
Hjelmquist & Morgan, 2012). Language has been termed an “instinct”, an innate ability that
is as specialised an adaptation as the spider’s web or the honeybee’s dance (Pinker, 1994). At
the same time we also know that the language-making instinct is sensitive to the richness and
type of input that the child receives (Hoff, 2006).
Language development in children follows a predictable pattern. Children assemble
their first phonemes in order to produce single words before they begin to combine those
words into sentences. They produce content words (such as nouns and verbs) before function
words (such as articles and prepositions) and construct short, grammatically simple sentences
before longer sentences involving complex constructions such as relative clauses (Brooks &
Kempe, 2012). The robustness of children’s language development is no more evident than in
the context of children learning signed languages, where with native exposure they follow a
similar pattern and achieve the major milestones at very similar ages to children learning
spoken languages (see chapters in Morgan & Woll, 2002; Schick, Marschark & Spencer,
2006).
There are individual differences in all aspects of cognitive development, and language
development is no exception. Fenson and colleagues (1994) report that the average Englishspeaking child produces his or her first word around 10-12 months of age and by 16 months
has a productive vocabulary of about 40 words. Nevertheless, individual children vary
considerably, with children at the 90th percentile producing around 180 words at 16 months,
whilst those at the 10th percentile produce only 10 words (Fenson et al, 1994). Similar
3
figures have been shown for Deaf children exposed to British Sign Language from birth (see
Woolfe et al, 2010).
Thus within the typical language-learning child population there is variation in rate
and patterns. We are able to track this with precision in many spoken languages because
normed tests of language development have been created. It is more challenging when the
language being acquired does not have these normed tests or when children are exposed to
more than one language at the same time, as is the case for the majority of young children in
the world.
At the same time there is developmental variability that goes beyond the bounds of
what is expected. A small minority of children in all languages will fall below the natural
bounds of language development. For example, van der Lely (1997) describes a case study of
an English-speaking hearing child who at the age of 5 produced just three words. Thus
normed tests also allow researchers and clinicians to pinpoint more serious and persistent
language learning disorders. There are various reasons why a child’s language development
might be thrown off its expected time-course. Those reasons can be external to the child, such
as poor quality language input, or they can be internal to the child (Hoff, 2006; Reilly et al,
2010). This chapter focuses on an internal or organic reason, Specific Language Impairment
(abbreviated to SLI). SLI is a developmental language disorder characterised by a delay in
language development that cannot be explained by low general intelligence, a sensory
impairment that would prevent language uptake, inadequate opportunity for acquiring
language, or a known neurological cause such as traumatic brain injury or epilepsy (Bishop,
2014; Reilly et al, 2014). SLI is known to be genetic in origin, although the aetiology is
complex and not yet well understood (Newbury, 2013). It can be diagnosed as young as the
preschool years (Reilly et al, 2010), and whilst for some children it will resolve, for others it
will persist into adulthood (Tomblin et al, 1992).
4
SLI has been researched in a large number of typologically diverse spoken languages,
including Cantonese (Stokes et al, 2006), English (Tomblin et al, 1997), French (Thordadottir
& Namazi, 2007), Gulf Arabic (Shaalan, 2010), Hebrew (Friedmann & Novogrodsky, 2004),
Russian (Tribushinina & Dubinkina, 2012), Swedish (Hansson, Nettelbladt & Leonard, 2000)
and Turkish (Rothweiler, Chilla & Babur, 2010). Recently there has been a growth in interest
and work on SLI in bilingual children (Armon-Lotem, 2010; Paradis, 2010). SLI has been
much less researched in signed languages, but several studies in British Sign Language (BSL)
have been published in the last 10 years, and the aim of this chapter is to summarise their
findings and to set out a description of what methods and personnel are needed for this
enterprise. This is an interesting topic both theoretically and practically. Understanding both
the universal and modality-specific characteristics of SLI will enable us to understand more
about the disorder in general. In practical terms it is crucial that professionals working with
deaf children are able to identify cases of SLI, particularly in the challenging contexts of late
language exposure.
The plan of the chapter is as follows. We begin by reviewing some of the linguistic
features of SLI across different languages. We then discuss issues involved in identifying and
researching SLI in the deaf signing population, which includes details about methods, testers
and analysis. The bulk of the chapter is given over to reviewing a set of studies of SLI in deaf
signers who use BSL, and a comparison of the profile of sign SLI to that of hearing children
with SLI in spoken languages. We conclude by setting out a roadmap for future research on
SLI in signed languages.
5
<1> SLI: diagnosis and cross-linguistic characteristics
Diagnosing SLI in any child is not straightforward (Williams & Lind, 2013). SLI is unlike
Down Syndrome, Williams Syndrome or Velocardiofacial Syndrome, for which the genetic
bases are well understood and where simple and accurate genetic tests exist for diagnosis.
Instead, SLI is like Developmental Dyslexia, Autism Spectrum Disorder, and Attention
Deficit and Hyperactivity Disorder (ADHD), which are behaviourally defined. A diagnosis of
SLI relies principally on assessing children’s performance on standardised tests of language.
However, this is more complicated than it might sound. Language abilities occur on a
spectrum, meaning that decisions have to be made as to where the cut-off between typical and
atypical performance lies, and such decisions have a degree of arbitrariness (Reilly et al,
2014). Decisions also have to be made as to which aspects of language are assessed: should
both language comprehension and language production be measured, and which of syntax,
morphology, vocabulary, pragmatics and phonology should carry most weight in the
assessment process (Dockrell & Marshall, in press)? All of these issues are very relevant for
studying SLI in deaf children’s sign language development as well.
The inclusion of “specific” in the term SLI is designed to indicate that this is an
impairment solely of language, or at least that the child has marked weaknesses in language
in comparison to non-language abilities .With respect to diagnosis, this means that alongside
the criterion that language is impaired, there are also various exclusionary criteria. SLI cannot
be diagnosed when the child has low non-verbal abilities because these might conceivably
affect the child’s language-learning abilities. Like language, however, non-verbal ability
occurs on a spectrum, meaning again that rather arbitrary decisions have to be made as to
what counts as “low”. SLI is frequently co-morbid with other developmental disorders,
meaning that children who have it are at increased risk of also having, for example, reading
difficulties (dyslexia and/or poor reading comprehension) and ADHD (Reilly et al, 2014).
6
Language impairment is also a common feature of autism. Such co-morbidity challenges the
notion of an impairment that is ‘specific’ to language and is the subject of massive debate in
the literature. How specific to language SLI actually is, becomes relevant when working with
deaf children who might have a suspected developmental disorder.
The complexities of diagnosis mean that even in hearing monolingual children there is
considerable debate about the exact criteria for a diagnosis of SLI, about whether those
criteria identify a homogeneous and coherent group of children, and even whether the term
‘SLI’ has scientific, clinical or educational validityi (Reilly et al, 2014). Nevertheless, it is
critical that children with low language levels are identified so that they can be offered
support from clinical and educational services. Different diagnostic criteria will, of course,
capture different proportions of children within their net, but estimates that SLI affects
approximately 7% of children at the age where they would start school (Tomblin et al, 1997)
are widely accepted.
The children who receive a diagnosis of SLI form a heterogeneous group with respect
to the severity and profile of the disorder (Leonard, 1988). One of the goals of SLI research
has been to uncover “clinical markers”, i.e. language characteristics that the vast majority of
individuals with SLI share, that persist even in individuals whose overt language difficulties
appear to have resolved, and which are heritable (Bishop, 2006). Three clinical markers have
been proposed for English-speaking children: omission of tense morphemes (saying, for
example, “Yesterday I walk” instead of “Yesterday I walked”, hence omitting the -ed suffix;
Rice & Wexler, 1996), inaccurate repetition of non-words (e.g. perplisteronk, a made-up
word which most children with typically developing language will repeat accurately the first
time they hear it, but which children with SLI are unlikely to be able to do; Bishop, North &
Donlan, 1996), and inaccurate repetition of sentences (Conti-Ramsden, Botting & Faragher,
2001).
7
Cross-linguistic research on SLI is valuable because it allows researchers to
investigate whether such clinical markers are relevant just for English or whether they are the
same for other languages too. In much of our own work on sign language SLI we have
followed this idea of identifying clinical markers based on spoken language research, and
have investigated whether these might be different in a signed language compared to a
spoken language. Different languages afford the possibility of different types of errors in
acquisition. For example, Chinese has no tense marking, so Chinese-speaking children with
SLI do not have the opportunity to make tense-marking errors. However, Chinese, in contrast
to English, is a tonal language. Might Chinese-speaking children make errors in their choice
of tone for words? Such comparative research is important because it allows us to look
beneath the surface characteristics of the language and gain insight into what is more
fundamental to the disorder, thereby gaining insight into what the underlying causes of the
disorder might be.
Cross-linguistic studies reveal that problems with inflectional morphology (and not
just tense marking) are characteristic of SLI in many languages, including Dutch, German,
Italian, and French (Crago, Paradis & Menn, 2008). Non-word repetition is also problematic
across a range of languages, including Dutch, Spanish and Swedish (de Bree, Rispens, &
Gerrits, 2007; Girbau & Schwartz, 2007; Kalnak et al, 2014). Several syntactic constructions
have also been found to pose problems for children with SLI in numerous languages,
including wh-questions (i.e. questions with ‘who’ ‘which’, or ‘what’, Schulz & Friedmann,
2011) relative clauses (i.e. the underlined portion of the girl who lives next door; Friedmann
& Novogrodsky, 2004) and passive sentences (i.e. ‘the dog was chased by the cat’; van der
Lely & Harris, 1990).
The picture of SLI that emerges from such cross-linguistic research, therefore, is of a
disorder that principally affects syntax, morphosyntax and phonology, and in which
8
vocabulary and pragmatic impairments may be present in some children but are less severe
(Leonard, 1998; Rice, 2013; van der Lely, 1997). Is this the same profile that we see in deaf
children acquiring sign languages?
<1> Studying deaf children with SLI
Our understanding of sign SLI is growing (for British Sign Language - BSL: Morgan,
Herman & Woll, 2007; Mason et al., 2010; Marshall et al., 2013; Marshall et al., in press;
Herman et al., 2104; and for American Sign Language – ASL: Quinto-Pozos, Forber-Pratt
and Singleton, 2011). Several years prior to setting up our own systematic study of SLI in
signing children, there were two areas of work that were very informative. Firstly, some of
our colleagues were documenting the existence of atypical sign language use in both children
and adults with developmental and acquired disorders. While these individuals had
difficulties in wider cognitive skills as well as language, they did give us a good grounding in
how to study this topic. Amongst these studies were reports of children with Down syndrome
(Woll & Grove, 1996) and deaf adults with aphasia (e.g. Atkinson, et al, 2005; Marshall et al,
2004). This early groundwork suggested to us that it was possible to study atypical sign
language and to compare atypical sign language users with hearing populations with similar
profiles (for an overview of this work, see Woll & Morgan, 2012).
Secondly, our colleagues in speech and language pathology practice were informing
us regularly of children whom they believed had SLI in their signing. Through our interaction
with speech and language therapists working with deaf children it became obvious to us that
children with language impairments above and beyond the expected range of language
variation were being identified and evaluated in clinics. Indeed, even children with native or
high quality sign language exposure early in development were being referred for
assessments. Thus we had developed some expertise in working with atypical signers and
9
there was a growing awareness that sign SLI might be a real disorder. In order to find
systematic evidence of sign SLI, however, there were several factors to deal with.
These were:
1. Late exposure to sign language is the norm for deaf children.
2. Few standardised sign language assessments are available.
3. The skills required from testers to identify sign SLI are very specialized and come
from multiple disciplines.
4. There is an incomplete understanding of the adult sign language system (i.e. the
target) with which to compare children’s development.
In the following section we expand on each of these in turn.
<2> Late exposure to sign language
The main stumbling block for studying the differences between delay and disorder in deaf
children is that the vast majority (90-95%) of deaf children who are exposed to a sign
language are born to hearing non-signing parents. This means that even in cases where
hearing parents learn BSL and sign with their children from an early age there will be
question marks over the quality and quantity of exposure to sign. We do not know how much
exposure to sign is necessary for typical development or whether primary language exposure
can come from adult non-native learners, and in general it is not completely clear what ages
are the most critical or sensitive for different aspects of sign language phonology and
grammar (Ferjan Ramirez, Lieberman & Mayberry, 2013; Morgan, 2014; Schick, 2004). In
sum, from the outset of studying sign language SLI it is important that one understands the
complexities of the population. The typical situation for a deaf child who learns a sign
language is late exposure to a less than optimal input. This means that if a child displays a
10
language delay, it is challenging to determine whether this is because of the late exposure (an
external factor) or because of SLI (a factor internal to the child).
In a wider context, disentangling language impairment from language delay is also a
challenge when studying hearing children who are exposed to two spoken languages at
different rates. Not all bilingual children have balanced exposure to both languages at all
stages of their development. While there is a general consensus that bilingualism in children
does not cause permanent language delays (Genesee, Paradis & Crago, 2004), some bilingual
children do have reduced input of one language temporarily during early language
acquisition, which slows down acquisition of that language. A proportion of such children
also have SLI, but it is difficult to diagnose SLI in children with uneven bilingual exposure
(Paradis, Schenider, & Sorenson Duncan, 2013; Bedore & Peña, 2008).
With respect to sign SLI, the best way to minimise the issue of impoverished input is
to look for SLI only in native signers. This was confirmed in an early case study of a native
signer who had very marked BSL delay (Morgan et al., 2007). Because this child had deaf
signing parents, his delayed language development could not be explained by late or
inadequate exposure to BSL. However, native signers make up a very small proportion of the
signing child population. It is not possible to exclude from studies of SLI deaf children who
have hearing parents, as this strategy would rule out 90% or more of the population.
<2> Paucity of standardised sign language assessments
In the wider SLI literature, diagnosis and profiling of cases of SLI relies on the use of
standardised assessments of language, both omnibus tests and tests of more specific
components of language such as syntax or vocabulary. In our sign SLI work we have used
standardised measures to eliminate children with low non-verbal cognitive abilities or
impaired motor difficulties that might contribute to their communication difficulties (see
11
Mason et al., 2010). In addition we used two standardised measures of BSL to confirm that
the children’s language development was significantly below that expected for their age i.e.
beyond natural variation.
However, sign language tests are currently fairly limited with respect to which aspects
of the language can be tested, compared to what is available for English. Worldwide, very
few standardised measures of sign language exist because of difficulties obtaining a
sufficiently large sample given the size and nature of the deaf population, and also because of
the limited research on sign language and sign language acquisition in many countries (Mann
& Haug, 2014). The exact same issue is present in studying SLI in many spoken languages,
for which no assessment tests are available.
We were fortunate in having two available measures (Receptive Grammar: Herman,
Holmes & Woll, 1999; Narrative production: Herman et al., 2004). For each, the
standardisation was based on a sample comprising deaf and hearing native signers, deaf
children in hearing families on bilingual (BSL/English) educational programmes, and deaf
children in hearing families on Total Communication programmes (using a range of
communication approaches including BSL and English-based sign systems). Since the
standardisation sample comprises, in the main, deaf children in optimal language learning
environments, performance on these tests was used as an initial and only preliminary
guideline. In subsequent testing of more specific aspects of signing, when we developed new
language tests but did not have access to a standardisation sample, children’s scores were
compared with those of children from the same schools. Both sets of children entered signing
environments at similar ages and came from comparable home language learning
backgrounds. This last point is important, because children with suspected SLI should be
compared on tests with children with the same background language histories and quality of
12
input. Furthermore, we are currently adapting the BSL narrative production test to spoken
English as in our recent studies many deaf children chose to narrate the story in English.
<2> Range of skills required from testers and researchers
It is important to stress that the systematic evaluation of language disorder in deaf
children in our work was made possible by two main factors: 1) A team of native Deaf and
hearing sign bilingual researchers, working closely with psychologists, linguists and
clinicians with skills in sign language linguistics, language and cognitive assessments, and 2)
the team’s knowledge of language acquisition in deaf and hearing populations. These areas of
expertise and skill were necessary at all stages in the identification of SLI in deaf signing
children, but we are aware that many professionals working with deaf children are not fluent
signers or do not have a strong background in SLI and language assessment. In this latter
scenario it is advisable a child with a suspected SLI in sign language be assessed by trained
specialists through a referral service.
However, it is often the case that referral to specialist services will not be possible.
Many cases where a deaf child has been identified with slower than expected language
development have been because of the gut instinct of the child’s parents, teacher or language
specialist. This was often the case in our initial work, where language pathologists working
with deaf children who signed informed us about children with severe sign learning delays.
Nevertheless we had to attempt a systematic evaluation of children using whatever resources
were available to us. If standardised assessments are not available, we advise a methodology
for differentiating delay and disorder based on comparing the suspected SLI case with
children who have received similar quantity and quality of exposure to a sign language on
some form of language measure (see Mann, this volume).
<2> An incomplete understanding of the adult sign language system
13
While no fully comprehensive linguistic analysis of any language has yet been completed,
this situation is more exaggerated for sign languages, where there are great gaps in our
knowledge and much disagreement. For example classifiers employ a particular handshape to
pick out a class of nouns (e.g. flat objects) and can be used to describe a whole sentence e.g.
‘the book is under the bed’. However there is a profound lack of consensus in the research on
classifiers in sign languages, with linguists disagreeing as to whether they are polymorphemic
or not morphological at all (see Emmorey, 2003; Morgan & Woll, 2007). This lack of clarity
as to how to describe different parts of the grammar extends to the status of pronouns, verb
agreement (inflectional morphology) and even to phonology. This means it is difficult to
know how to best conceptualise different language structures and to know what to expect of
their acquisition in deaf children who sign, and this also slows down psycholinguistic work
on the language.
More generally, confusion arises when distinguishing signs from communicative
gestures even in linguistic descriptions of adult native signers. The role of gesture in a
grammar of a sign language is crucial for studying SLI. Describing linguistic skills can be
especially difficult in children with limited signing who are adept at using the visual modality
creatively to communicate. For example, if a deaf child uses mime, how is this different to
what linguists call ‘constructed action’ (Quinto-Pozos, 2007)? In the first SLI case we
reported (Morgan, et al, 2007), we observed that Paul used exaggerated gestures and facial
expressions in spontaneous interaction. We argued this was a strategy to compensate for his
poor linguistic competence, making his impairments less noticeable. He often used pointing
to pictures, to himself and to others in lieu of full sentence structures. In addition Paul used
more affective facial expression instead of the specific face and head linguistic markers, for
questions, negations or manner modifications with verbs (for a recent example of this face
strategy in deaf children with autism, see Denmark, et al, 2014).
14
With these four factors outlined, we hope to have highlighted issues that we dealt with
during the evolution of our research studies. We suggest it is important to be aware of these
four factors before embarking on the study of sign SLI. With this background complete, the
next section outlines findings from a series of studies on groups of signing children who have
SLI. Some children appeared in several studies allowing us to begin to develop profiles of
impairment. Our aim in this chapter is to compare what we have found in BSL with what is
known for these same linguistic domains in spoken languages.
<1> Phonological skills
The first component of sign language that we discuss here is phonology. Phonology is the
level of linguistic organisation below the morpheme or word, and which organises the
medium through which language is transmitted: be that vocal/auditory in the case of spoken
languages or manual/visual in the case of signed languages. In signed languages, the units of
organisation are generally considered to be handshape (i.e. the configuration of the hand),
orientation, location, movement, and non-manual features (Brentari, 1998; Stokoe,
1960/2005).
As we explained earlier, a marked difficulty in repeating non-words (i.e. spoken
forms that follow the phonotactics of a particular language but have no meaning) is a robust
feature of SLI in many languages (de Bree, Rispens, & Gerrits, 2007; Gathercole &
Baddeley, 1990; Girbau & Schwartz, 2007; Kalnak et al, 2014).). Repetition is particularly
difficult when the non-word is phonologically complex and contains phonological structures
that are late-acquired, for example, consonant clusters and/or unusual stress patterns (Bishop,
North & Donlan, 1996; Gallon, Harris & van der Lely, 2007)
We investigated the manual phonological abilities in deaf signing children with and
without SLI, using a test of non-sign repetition with non-signs at different levels of
complexity (Mann, Marshall, Mason & Morgan, 2010; Marshall, Denmark & Morgan, 2006;
15
Mason et al., 2010). Non-signs are manual forms that fit the requirements for being signs but
are not known as existing signs in BSL. There are not exact parallels between phonological
complexity in spoken and signed languages but our non-signs differed in whether they
contained an unmarked or a marked handshape (markedness can be defined as a sign which is
more difficult to articulate and perceptually complex and is predicted to be more difficult to
repeat). They also differed in whether they had a single movement (either path or internal
movement) or a movement cluster (i.e. path plus internal movement, which again is predicted
to be more difficult to repeat). An example of a BSL non-sign with a marked handshape but a
single movement is shown across the two stills in figure 1.
----------------INSERT FIGURE ONE HERE------------------
The non-sign repetition test has norms derived from 91 deaf children ages 4-11 years
(see Mann et al., 2010 for more details). In Morgan et al.’s (2007) case study of a native
signer, the subject, whom we called Paul, performed extremely poorly on the non-sign
repetition test (see Woll & Morgan, 2012). We tested a group of deaf signers with suspected
SLI on the same test in Mason et al., (2010) to see if poor non-sign repetition could be a
clinical marker for sign SLI (using the process outlined in section 2 previously). Of the 13
children tested only 5 demonstrated impaired non-sign repetition, where “impaired”
performance was defined as a score lower than one standard deviation below the mean.
Thus it appears that repeating non-signs is a weak skill in only a subset of our sample
of sign language users with SLI, as opposed to being a clinical marker as has been reported
for spoken language SLI. At first glance, the performance of our group of SLI children on the
non-sign repetition task, on which the majority performed comparably to typically developing
deaf controls, might appear to challenge the hypothesis that SLI is caused by a phonological
16
short term memory deficit (Gathercole and Baddeley, 1990). However, as we have argued
elsewhere (Marshall et al., 2011), the repetition of non-signs appears to be a difficult task
even for typically developing deaf children. Our explanation for this difficulty is that the
phonological content of a non-sign is less predictable than the phonological content of a
spoken non-word, and therefore its retention in short term memory is more cognitively costly.
The basic idea here is that signs in BSL may have fewer limiting constraints than spoken
language words with respect to how their sub-lexical components can be combined. In a
sense there are more degrees of freedom for how sub-components combine in a sign than a
word and this makes processing demands higher (Marshall et al., 2011).
A developmental impairment in processing at the phonological structure of a sign
might lead to impairments at several levels of the language, with one consequence being on
the acquisition of new signs and the construction of the lexicon. If a child does not lay down
good phonological representations, then building up a lexicon will be more difficult and
accessing that lexicon in different contexts will be compromised. This leads us onto studies
of lexical skills in children with SLI.
<1>Vocabulary and semantic fluency
In studies of spoken language SLI, profiles of impairment are heterogeneous, for
example more children have impairments in expressive vocabulary than in receptive
vocabulary, although not all children with SLI have vocabulary difficulties. Nevertheless,
impaired vocabulary acquisition and word production are found in some children with SLI
(Marshall, 2014).
We were initially surprised to find that the native signer with SLI reported in Morgan
et al (2007) had relatively unimpaired vocabulary. We assessed Paul’s receptive vocabulary
using a non-standardized BSL version of the British Picture Vocabulary Scale (Dunn et al.
1982). His receptive BSL vocabulary was normal for his age, when compared to norms
17
collected from groups of normally developing signing children. We decided to look at
vocabulary knowledge in other ways by developing a semantic fluency test for BSL.
Research on hearing children with SLI has investigated the speed and accuracy of
their lexical access skills using fluency tasks (Henry, Messer & Nash, 2012; Messer &
Dockrell, 2013). In a semantic fluency task, participants are asked to produce as many words
as they can from a specific semantic category, such as ‘animals’ or ‘food’ within a limited
time period, most usually one minute. The test gives an indication of children’s semantic
organisation: if they are able to generate exemplars in response to a superordinate label, e.g.
‘animals’ or ‘food’, then this suggests that their semantic knowledge is organized
taxonomically. Furthermore, they often generate words in bursts of semantically related
clusters of items, for example “cat, dog, rabbit, cow, horse, sheep, hen, duck…” (in this
example, a cluster of pets followed by a cluster of farm animals), which suggests that
semantically-related words are stored close together in the lexicon. In hearing children with
SLI, there is evidence that at least some children generate fewer words during the course of
the minute than their chronological age matched peers, suggesting a difficulty accessing
either the phonology or the semantics of the word, or both (Henry et al, 2012; Messer &
Dockrell, 2013).
We used the semantic fluency task in BSL, with the categories “food” and “animals”
as these are amongst the most commonly used categories in the spoken language literature.
We tested 22 typically developing deaf signing children, aged 4 years to 15 years, and a
group of 13 deaf signers with SLI, aged 7-14. Our findings indicated no differences between
the SLI group and a subgroup of age-matched typically developing deaf signers in terms of
overall numbers or types of responses (Marshall et al., 2013). This mirrors what we found
with Paul’s receptive vocabulary. However, subtle differences were observed: the SLI group
18
produced fewer signs in the first 15 seconds than their typically developing peers and there
was also some evidence of word-finding difficulties in the SLI group, suggesting that their
access to signs was slower and less accurate. For example, a 14-year-old child signed
MOUSE IN WHEEL – YOU KNOW and 7 seconds later retrieved HAMSTER. Another 14year-old created many compound signs, some of which were real items (DOGFISH,
CATFISH, GOLDFISH), but others were not (REDBERRY, SEABIRD). A third child, aged
9, signed ORANGE BUT NOT HORSE, and never found the correct sign for the animal she
was searching for.
Our conclusion is that the deaf children with SLI who participated in this study did
not differ from those without SLI in terms of the semantic organization of the BSL lexicon (at
least, the limited part of the lexicon that we investigated), but that they accessed signs less
efficiently. It is not clear from our data whether this is due to slower access to the semantic
component of the sign, or to less efficient mapping from the semantic to the phonological
form, meaning that the phonological form of the sign is retrieved more slowly or not at all.
This matter is also subject to debate in the spoken language literature (Marshall, 2014).
<1> Syntax and morphology
One major area of language difficulty in hearing children with SLI is in their understanding
and use of grammar. Indeed, the areas of syntax and inflectional morphology (i.e. the use of
morphology on verbs to mark person and tense information e.g. third person singular ‘s’ and
past tense marker ‘ed’) have been the most widely-studied in the SLI literature. Studies
consistently report that hearing children with SLI have impairments in syntax and inflectional
morphology that are more severe than their impairments in other components of language
such as vocabulary. This means that not only do children with SLI score lower than their
chronological age-matched controls on tests of syntax and morphology, but they also score
19
lower than younger typically developing children matched for scores on a vocabulary test (for
a review, see Leonard, 1998).
As we discussed earlier, the sorts of syntactic constructions that pose problems for
children with SLI include wh-questions, relative clauses and passive sentences (Schulz &
Friedmann, 2011; Friedmann & Novogrodsky, 2004; van der Lely & Harris, 1990). In
English, the omission of the past-tense morpheme –ed is common in SLI. All these
constructions have in common the features of being grammatically complex and acquired
relatively late by typically developing children. Impairments are consistently found across a
variety of measures, including comprehension tasks and production tasks such as sentence
repetition and narrative elicitation.
In Morgan et al. (2007) we reported that Paul’s comprehension of BSL grammar was
1.3 standard deviations below the mean compared with the standardised scores for children of
his age. In addition, his performance was atypical or of a different quality to other signers,
with success on some difficult items and failure on many easier ones. His performance could
not be characterized as that of a younger learner, as by failing early items and passing more
difficult ones his performance actually appeared random.
Analysis of Paul’s sentence production in a conversation sample and elicited picture
descriptions revealed that his expressive BSL was restricted to small sentences made up of
one or two signs with very limited grammar. Despite this, Paul clearly enjoyed
communicating and provided a range of appropriate affective (but non-linguistic) facial
expressions and gestures. This supported our assessment that he was not autistic. Here we
show examples of Paul’s descriptions from the picture tasks to an adult Deaf native signer,
compared with similar age typically developing deaf children.
Target picture: a dog in a box.
20
Paul: DOG whole body gesture with hands on the head (top of box)
Adult: DOG WHERE?
P: whole body gesture to show looking up
A: PICTURE WHAT?
P: BOX
A: AND?
C: DOG
A: DOG WHERE?
P: looks away and changes topic
Typically developing native signer aged 4;6:
C: POINT (picture) CL-(cube)-CL-(small animal)-SIT-IN-BOX
English Translation: ‘there, the dog is in the box’
Target picture: a man giving a boy a letter.
Paul: GIVE GIVE SQUARE GIVE (citation forms)
A: SQUARE GIVE WHO?
C: GIVE GIVE POINT (picture) LETTER
A: PICTURE WHAT?
C: LETTER POINT
Typically developing native signer aged 4;6:
C: MAN LETTER GIVE-3rd person agreement
English Translation: ‘the man gives the letter to (him/her)’
21
Sentence repetition requires the child to repeat back a sentence as accurately as they can as
soon as they have heard it spoken by the assessor, and it has been used across a range of
spoken languages. In a later group study of children with sign SLI we reported impaired
performance on morpho-syntactic aspects of BSL by using a sentence repetition paradigm
(Marshall et al., 2014).
The child BSL sentence repetition test required children to repeat 20 signed sentences
(including 3 practice items). Marshall et al. (2014) reported across the board impairments for
11 deaf children of hearing parents aged 7;4-12;9 with sign SLI compared with age-matched
non-impaired controls. The stimuli to be repeated by children were presented on a video and
consisted of 20 sentences with differing degrees of complexity attuned to the language agerange of the participants. Significant group differences were found for each linguistic
element coded for: lexical content, spatial morphology, sign order, sentence meaning and
facial expression. Previous work using sentence repetition in spoken languages has
emphasised that verb morphology is difficult for children with SLI. We therefore looked in
more detail at this component of BSL grammar. On the sign test the highest score for
repeating sentences that included classifiers and agreement verb morphology was 9. There
was a significant difference between the SLI group’s mean (4.27 points) and the control
group’s (6.00 points). See Marshall et al. (2014) for more details.
<1>Narrative
The highest level of language organisation we investigated in sign SLI is narrative
production. In contrast to conventional language tests, which elicit production and test
comprehension using artificial tasks, narrative tasks provide a more naturalistic setting to
examine children’s language skills (Dockrell & Marshall, in press). Because of the challenges
posed to young children in constructing a coherent narrative, these tasks have been used to
22
investigate patterns of SLI in spoken languages (e.g. Botting, 2002; Wetherell, Botting &
Conti-Ramsden, 2007).
English speaking children and adolescents with SLI have been reported to produce
narratives similar to those of younger typically developing children (Merritt & Liles, 1987;
Wetherell et al., 2007). For example, Marini, Tavano and Fabbro (2008) found that they
produced narratives with less developed sentence structure and use of verb morphology, and
that they had problems with the anaphoric use of pronouns.
In Morgan, et al (2007), Paul’s performance on the BSL Narrative Production Test
(Herman et al, 2004) was at the 25th centile for all criteria (grammar and story structure
elements). When we separated the grammar and story structure scores (introducing the
characters, building up to a climax, providing a story coda, etc.) he scored higher in these
elements (22/34 - 65%) than in his BSL grammar (9/30 - 30%).
Thus it might have been the case that children with sign SLI are less weak in
pragmatic aspects of language particularly in narrative. However in a recent larger study of
sign SLI we in fact did not confirm this earlier prediction. Herman et al (2014) investigated
the narrative skills of a group of 17 deaf children with sign SLI with a mean age of 10 years
(range = 5;00–14;8). All children were from hearing parents and had been exposed to BSL
before age of 5 (mean years of exposure = 6;6, range = 3;8–9;0). This group was compared
with a control group of 17 deaf child signers matched for age, gender, education, quantity,
and quality of language exposure and non-verbal intelligence. Children were asked to
generate a narrative based on events in a language free video (the BSL production test –
Herman, et al, 2004). Narratives were analysed for global structure, information content and
local level grammatical devices, especially verb morphology.
The language-impaired group produced shorter narratives (mean 26 clauses) than the
non-impaired signers (mean 45 clauses). There were also significant differences in the
23
structural quality of the narratives between groups. For example at the start of the story good
narrators set the scene (identify the main participants and objects). We see this in a sample
from a 12 year in the control group. CL refers to classifier signs, LOC are specific locations
in sign space:
GIRL WALK-CARRY-TRAY (body movement indicating walking, using CL-HOLD-TRAY
at the same time) ROLE SHIFT OH THERE (point to location of table) PUT-DOWN-TRAY
(CL-HOLD-TRAY) ON TABLE HMM (strokes chin) WHICH FOOD BOWL (LOC-1)
LOTS SWEETS LOC-2 (CLPLATE) SANDWICH LOC-3 (CL-PLATE) CAKE
“So the girl carries in a tray of food and places it on a table nearby. She thinks to herself
‘which bowl should I fill with sweets?’ She puts the bowl over there, the plate of sandwiches
here and the cake next to it”.
In contrast we do not see this scene setting or clarity in the next example from a
similar part of the story recounted by a 12 year old child in the SLI group:
WALK (the handshape used is unclear as the child uses two hands instead of one) SIT SIT
(different locations to show two people) BOY LAZY HANDS-TOGETHERLEAN-HEAD-ON-SOFA (use of gesture to describe boy’s actions) WATCH-TV (unclear
handshapes) HE DEMAND DEMAND (unclear articulation which looks like the sign
DON’T-KNOW) GIRL WALK
“Comes in and they sit, the boy is sat lazily with his head back watching TV. He keeps asking
for things and the girl goes over there”.
In all the aspects of the BSL narrative components, SLI children were worse than
controls i.e. semantic content, grammar including use of classifiers and role-shift (see
Herman et al, 2014 for more details). Lastly in terms of pragmatic inferences we also found
that the SLI children were worse at demonstrating an understanding of the motives of the
characters in their own stories. We tested this by asking children to answer questions about
24
their stories which required some inference making. For example, the last question on the test
is: ‘Why did the girl tease the boy’? The answer to this question is not supplied in the video
stimuli but instead requires some perspective taking abilities and touches on Theory of Mind.
A correct response would be ‘She wanted to surprise him’ and an incorrect one would be
something like ‘The girl was naughty’ which only gives superficial information on
motivations of the characters. Scores for answering these questions, where the maximum
level is 6 points, were: SLI group mean 1.73 points and control children: mean 3.25 points.
Similar difficulties in inference making have been reported for children with SLI in spoken
languages (e.g. Norbury & Bishop, 2003).
<1>Conclusions
In this chapter we have detailed the growing evidence that sign SLI exists. In fact from our
group study we estimated a prevalence rate for SLI in BSL of 6.4% (Mason et al., 2010). This
is similar to the prevalence rates reported by Tomblin et al. (1997) for the hearing population.
As we stated in the introduction, understanding both the universal and modalityspecific characteristics of SLI will enable us to understand more about the disorder in
general: explanations of SLI must be able to account for both the spoken and signed
modalities. The existence of SLI in a signed language, as we have argued elsewhere (Mason
et al., 2010), is problematic for theories of SLI that claim that children with SLI have
language impairments because they cannot process the rapid temporal changes in speech as
efficiently as their non-language-impaired peers. The visual system does not have the same
temporal resolution as the auditory system. Finding SLI in a signed language does not, of
course, prove that temporal processing deficits do not cause SLI in hearing children, but it
provides support for the view that at least some cases of SLI have an underlying cause that is
not tied to one modality.
25
As we also stated at the outset, the study of sign SLI has revealed a complex and
interesting picture of the disorder. Further, in some aspects of sign we see parallel levels of
breakdown across modalities (verb morphology and syntax) while in other aspects we see no
such consensus (phonological processing). We have argued this is characteristic of the
typological differences across BSL and some spoken languages e.g. phonology might be
organized differently in BSL than it is in English making different demands on the processing
of the stimuli between modalities. Finally studying this disorder is also complex because of a
set of issues related to the language, the child, the testers and the tests.
When studying spoken languages, a lot is generally known about the adult target and
typical child language development, and the path for attaining the adult target, the degree of
variability, ages of acquisition of different words, grammatical morphemes and syntactic
structures, etc, are known. For many spoken languages (although by no means all) a large
number and variety of language assessments are available (Dockrell & Marshall, in press).
This is rarely the case for signed languages. This means that a multi-faceted approach –
experimental studies in psycholinguistics, corpus-studies, development of signed language
assessments, detailed case studies, etc. – is crucial.
Our work to date has been cross-sectional, meaning that our data on each child are
limited to one point in a child’s development. There is a real need for longitudinal studies
tracking sign language development in children with SLI over time (plus typically developing
deaf children in comparison). Rice (2013, p.225) points out that data from a large
longitudinal study of hearing monolingual English-speaking children in the USA suggests
that “once acquisition of a particular language dimension begins, the children with SLI
follow, on average, the same growth trajectories as children without SLI” – i.e. the gap
between SLI and typical does not get wider, though nor does it close, over time. We cannot
26
assume that this would be the case for sign SLI, where sign input that the children are getting
may be of lower quantity and quality compared to what would be the case for hearing
children with SLI.
Finally, there is a chronic need for research into language interventions for children
with SLI in signed languages. Although there is no “quick fix” for SLI in spoken languages,
there is a growing evidence base of what works and what does not with respect to language
interventions (Law et al., 2003; Law et al., 2012). The recommended methodology for
evaluating the efficacy and effectiveness of interventions is the randomised control trial (Law
et al., 2003), i.e. studies whereby children are randomly allocated to groups and where a
comparison can be made between a group who receives the intervention and a group who
does not. Randomised control trials require preliminary studies before they can be
undertaken, but it is our enduring aim that others will take up this challenge in BSL and in
other signed languages. It is hoped that the initial work that we have outlined in this chapter
assists in this endeavour.
27
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native signers: a British Sign Language adaptation of the communicative development
inventories. Journal of Child Psychology and Psychiatry, 51, 322-331.
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Figures and tables
Figure 1. Example of a nonsense sign in BSL. The clips show the start and end positions and
the arrow shows the path of movement.
i
Indeed, there is debate over which term should be used, with other terms such as ‘primary
language impairment’, ‘developmental language disorder’, ‘speech and language difficulties’,
‘speech and language disorder’ and ‘developmental dysphasia’ being used in the research
and applied literature (Bishop, 2014). We use the term ‘specific language impairment’
throughout this chapter, whilst recognising that other researchers may prefer another term.
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