int. j. lang. comm. dis., 2001, vol. 36, no. 4, 421–432
Non-word repetition and language
development in children with speciŽ c
language impairment (SLI)
Nicola Botting and Gina Conti-Ramsden
University of Manchester, Manchester, UK
(Received December 2000; accepted March 2001)
Abstract
Non-word repetition has previously been found to correlate with language
outcomes both in children who are language impaired and in those who are
developing normally. This paper concerns a group of children identiŽ ed as
having speciŽ c language impairment (SLI) and follows the methods of Adams
and Gathercole (2000) by taking children with the highest and the lowest nonword repetition scores at age 11. These children’s language and literacy abilities
were then compared. Despite the fact that high and low scorers were matched
on Performance IQ tasks (Block Design and Picture Completion), all linguistic
measures except for vocabulary assessments showed signiŽ cant diVerences
between the groups. The fact that these diVerences were present despite block
design scores being identical for the two groups suggests that more than a
general working memory deŽ cit underlies the language diYculties. Furthermore,
signiŽ cant diVerences were noted on a digit-span task requiring processing and
production of number words. A speciŽ c phonological memory diYculty may
therefore be present over and above a subtle but more general processing
limitation. The implications for SLI theory and practice are discussed.
Keywords: speciŽ c language impairment (SLI), non-word repetition, memory,
language development.
Introduction
SpeciŽ c language impairment (SLI) is currently deŽ ned using exclusionary criteria,
that is, a deŽ cit in language in the absence of a number of other diagnostic features
such as hearing loss, autism and cerebral palsy (Leonard 1998). Since theorists and
clinicians are dissatisŽ ed with this deŽ nition, methods of positively identifying the
limitations experienced by individuals with SLI have been investigated by recent
Address correspondence to: Nicola Botting, Human Communication and Deafness, School of
Education, University of Manchester, Oxford Road, Manchester M13 9PL, UK;
e-mail: [email protected]
International Journal of Language & Communication Disorders
ISSN 1368-282 2 print/ISSN 1460-698 4 online © 2001 Royal College of Speech & Language Therapists
http://www.tandf.co.uk/journals
DOI: 10.1080/1368282011007497 1
Nicola Botting and Gina Conti-Ramsden
422
research. One tool that has received much attention in relation to language development is non-word repetition, which is thought to re ect some of the underlying
cognitive diYculties of SLI, perhaps those concerned with working memory,
phonological memory or long-term word knowledge (Gathercole 1995). Some
research is beginning to suggest that non-word repetition may be useful as a genetic
marker for language impairment (Bishop et al. 1996, 1999, Conti-Ramsden et al.
2001c).
However, relatively little work has been completed that directly analyses the
language abilities of children who have good non-word performance compared with
matched peers with poor scores. An important exception is the work of Adams
and Gathercole (2000), who showed that typically developing children with high
and low non-word scores were indeed signiŽ cantly diVerent on language measures.
Furthermore, because they also included non-spoken response tasks in their design,
they concluded that the data from their study did not support theories suggesting
that the relationship results solely from phonological output demands. Adams and
Gathercole suggested that further work needs to be undertaken investigating
‘performance limitation accounts of children’s speech production’ in language
disordered populations.
Interestingly, other authors are also investigating the cognitive aspects of language disorders. Ellis Weismer et al. (1999), for example, examined the verbal
working memory abilities in typically developing children and peers with language
impairment. They did not use a non-word repetition measure, but found signiŽ cant
diVerences on a ‘competing language task’ in which increased memory demands
were placed on the children. The paper concluded that the children with SLI showed
greater deŽ cits in verbal working memory and called for further research into the
relationship between memory and actual language diYculties.
Furthermore, the relationship between non-word repetition and language development also has implications for literacy abilities. Snowling et al. (2000) reported
signiŽ cant associations between performance on this task and reading ability. Nation
et al. (1999) showed that children with low reading comprehension scores also
performed poorly on verbal memory tasks despite the fact that groups of good and
poor comprehenders had been matched for decoding skill. Thus, the implications
of short-term memory deŽ cits may stretch beyond diYculties with oral language
development, into the area of literacy skill.
The present study investigates the relationship between memory and language/
literacy development in a sample of children with SLI who have either very good
or very poor phonological memory as evidenced by their performance on a nonword repetition task. The aims are twofold: Ž rst, to establish whether non-word
performance is related to actual language level in this population, excluding the
eVect of non-verbal ability, and thus validate its usefulness as a clinical tool; and
second, to examine the relationship between non-word repetition and literacy skills.
Method
Participants
Whole cohort
Around 500 children were identiŽ ed at 7 years of age as attending a primary
(attached to mainstream) language units in England. A random 50% sample of
Non-word repetition and SLI
423
these were contacted through schools and asked to participate in the study. These
children were assessed in school at 7 and 8 years (Conti-Ramsden et al. 1997, 1999a,
b) and were contacted again in their Ž nal primary school year (Year 6) and again
invited to participate in the project follow-up (Conti-Ramsden et al. 2001a). Thus,
no speciŽ c ‘SLI’ criteria were used at selection, except that those with known
current hearing loss and/or major physical disability were excluded as were those
with deŽ nite diagnoses of autism or of moderate learning diYculties. In total, 200
of the original 242 (83%) participated at the 11 Year stage, 50 (25%) of whom were
girls. Twenty-four children (12%) had exposure to languages other than English at
home. The average age of the children was 10:11 years (SD 5 5 months).
Subsample referred to in this paper
For this study, we wanted to compare children with the most extreme scores on
the Children’s Non-word Repetition task (CNRep) (Gathercole and Baddeley 1990)
partly to validate its use as a predictor of oral language skill in children with language
impairments. Adams and Gathercole deŽ ned their groups using children who scored
at least 1 SD above the group mean and those scoring at least 1 SD below this
mean. In the present study, data from a normative comparison group of the same
age was available (Simkin and Conti-Ramsden 2001) and since these data were
heavily skewed, groups were formed using equivalent cut-oV levels of below 16th
centile for age (low scorers) and above 84th centile for age (high scorers). However,
the normative group median was 38/40 and 84th centile fell at ceiling (40/40).
Thus, any children from the SLI sample scoring 40 or 39 (one error only) were
identiŽ ed. This totalled 14 individuals. The 16th centile threshold was a raw score
of 35, and 147 ‘low scorers’ fell below this cut-oV.
Matching of groups
Children with SLI were tested using subtests of the Wechsler Intelligence Scale for
Children (WISC-III; Wechsler 1992): Block Design, and Picture Completion. These
scores were then combined to form an estimated performance or non-verbal IQ.
This performance ‘short form’ in particular has been found to correlate well with
a full IQ battery and has been used in other studies of cognitive ability and language
(Sparrow and Davies 2000). The 14 high scorers were matched on this composite
score with a child from the low scorers pool (n 5 147). All but two children had
identical PIQ matches. These remaining two children were high scorers with
particularly high performance scores ( > 130). However, even these two individuals
were matched within 5 IQ points to low CNRep scoring children. This gave 28
children, 14 in each non-word repetition group.
Measures
Key task
Children’s Test of Non-word Repetition (CNRep) (Gathercole and Baddeley 1990). This
is a test of verbal/phonological short-term memory consisting of 40 non-words.
The non-word task was completed using live presentation of words as follows.
Children were told that the researcher was going to say some ‘made-up words’ and
were asked to copy them exactly. The researcher also explained that to stop the
424
Nicola Botting and Gina Conti-Ramsden
child getting any ‘clues’ from lip movements, she would also be covering her mouth
with a piece of paper. The two practice items were then given. All responses were
audiotaped and scored later that day. No repetitions of any words by the researcher
were allowed.
Language measures
Past tense task (PTT) (Marchman et al. 1999). This is a test designed to assess correct
grammatical usage of verbs in past tense form (e.g. he cleaned) and was developed
by Marchman et al. It consists of 52 line drawings shown to the child one at a time.
With each picture, the assessor reads out a sentence related to the picture, which
the child must complete. The items are balanced and randomized for frequency of
verbs and for regular vs. irregular forms.
Third person singular task (TPS) (Simkin and Conti-Ramsden 2001). Fifteen colour
photocards of people at work are shown to the children one at a time. As with the
past tense task, a sentence is read by the assessor, which must be Ž nished by the
child. It is the second test in the battery to assess tense marking.
Clinical Evaluation of Language Fundamentals Revised—Recalling Sentences Subtest (RecS)
(Semel et al. 1987). For this task children are given a sentence and asked to repeat
it verbatim. Sentences become increasingly longer and more complex. Responses
are scored in relation to the number of errors made in each sentence.
Expressive Vocabulary Test (EVT) (Williams 1997). An assessment for expressive
vocabulary that covers a wide age range (2 years–adult). Children are shown a
picture and told a key word by the assessor. The child must then elicit another
appropriate word that matches both the picture and the key word.
British Picture Vocabulary Scale (BPVS-II) (Dunn et al. 1998). This is a widely used
standardized test of vocabulary comprehension. Children are shown four line
drawings and asked to choose the one which best illustrates a word spoken by the
assessor. The vocabulary is given in blocks of twelve which become progressively
more diYcult, and children must score > 4 to continue to the next block.
Test for Reception of Grammar (TROG) ( Bishop 1982). This is a multiple-choice test
designed to assess understanding of grammatical constructions. Children are shown
four pictures while the examiner reads a sentence. The child is asked to pick the
picture that illustrates the sentence. Scores are given in age-adjusted percentile
ranges (e.g. 5th–10th percentile). For ease of statistical comparison, in the present
study these ranges have been transformed further into percentile midpoints for that
range (e.g. 5th–10th percentile becomes 7.5th percentile).
Literacy assessments
Wechsler Objective Reading Dimensions (WORD) (Wechsler 1993). Each child also
completed the Basic Reading and Reading Comprehension sections of this assessment. The Ž rst requires children to read aloud single unrelated words of increasing
complexity. For the second, children read a passage either out loud or in silence
Non-word repetition and SLI
425
and are then asked a question relating to the prose. Again, the items given increase
in complexity. Children are not scored on reading accuracy for this part, only on
response to the comprehension question. Scores are given as standard or centile
scores.
Procedure. Following written parental consent, and agreement with the child’s
teachers, children were seen individually in a quiet room or area of school. Breaks
were taken where appropriate. All children completed all the tasks and therefore
there is no missing data in this study.
Results
Language assessments at 11 years
Mann–Whitney comparisons across the high and low scorers revealed that most
tests of language at 11 years were signiŽ cantly diVerent according to non-word
repetition performance. This was not true for either the expressive vocabulary test
( EVT) or receptive vocabulary (BPVS) measures, although for both these measures
high CNRep scorers had medians within the normal range ( > 16 centiles) whilst
low scorers did not. Table 1 shows the medians interquantile ranges (IQR) on each
test by group.
Literacy assessments at 11 years
Basic (sight) reading and reading comprehension scores were also found to diVer
signiŽ cantly across groups. Figure 1 shows median basic reading scores of 61 centiles
( IQR 5 28.5–86) for the high CNRep scorers and 4 centiles (IQR 5 2.5–8.5) for
the low scorers ( p < 0.001). Reading comprehension shows a similar but less marked
pattern with median centile scores of 21 (IQR 5 5.5–59) and 4 (IQR 5 1–8) respectively ( p < 0.05). Importantly, these scores represent not merely a statistical diVerence
but a marked diVerence in the functional reading levels of the groups. Scores of
< 5 centiles are indicative of very little functional reading ability.
Cognitive assessments at 11 years
Children were matched for composite performance IQ using Block Design and
Picture Completion subtests. Subtests scores can be converted into IQ standard
score equivalents (IQ points) and these have been used in preference to centiles
because of the widespread use and understanding of IQ points where 100 (15) is
Table 1. Eleven-year language assessment median centiles (IQR) for high and low scorers
High scorers
EVT
BPVS
Past tense
Third-person singular
TROG
CELF recalling sentences
27
40
50
> 25
50
25
(1.5–38)
(10–64)
(16–90)
( >25– >25)
(37.5–95)
(7–50)
Low scorers
p
12 (2.5–20)
13 (5.5–30)
7.5 ( <1–25)
10 (2.5–16)
10 3–31.25)
2 (1–2)
0.306
0.114
0.012
0.003
0.024
0.001
Nicola Botting and Gina Conti-Ramsden
426
Figure 1. Reading scores (medians and IQRs) for high and low scorers.
the population mean (SD). Thus, Block Design showed an identical median IQ
point equivalent for high and low scoring groups (99, IQRs 5 85–129.5 and 85–119
respectively, p 5 0.91) and Picture Completion also showed identical standard scores
(107, IQRs 5 92–136 and 78–133.5 respectively, p 5 0.95). Despite being matched
for non-verbal ability, some items assessed from the verbal section of the WISC
were found to diVer across groups. Namely, Digit Span on which high CNRep
scorers achieved a median IQ point equivalent of 105 (IQR 5 90.5–112) and low
scorers a median IQ standard score equivalent of 82 (IQR 5 70–90.5; p < 0.01) and
Vocabulary for which high scorers had a median IQ point equivalent of 88 compared
with 70 for low scorers ( p < 0.05). The Comprehension subtest IQ equivalent scores
of the WISC were not signiŽ cantly diVerent (82 versus 65; p 5 0.51).
Assessments at 7 years and change from 7 to 11 years
At age 7, children had also been tested on a battery of standard language tests
( table 2). These were the Test for Reception of Grammar (as described above), The
Naming Vocabulary and Single Word Reading subtests of the British Ability Scales
( Elliot 1983), the Goldman–Fristoe Test of Articulation (Goldman and Fristoe
Table 2. Seven-year assessment median centiles (IQR) for high and low scorers
High scorers
BAS Naming Vocabulary
Goldman Fristoe test of Articulation
TROG
Bus Story Information
Single word reading
Raven’s coloured matrices
30 (24–36)
32 (24–48)
25 (10–37.5)
17.5 (5–37.5)
70.5 (36–99)
92.5 (75–97.5)
Low scorers
19 (10–34)
19 (10–42)
37.5 (17.5–37.5)
5 (5–17.5)
36.5 (5–48)
62.5 (50–92.5)
p
0.42
0.01
0.87
0.24
0.05
0.11
Non-word repetition and SLI
427
1986) and the Renfrew Bus Story Test (Renfrew 1991). DiVerences were found
between groups at 7 years on two of the Ž ve tests: single-word reading and
articulation where high scorers had a higher median centile score than low CNRep
scorers. The three remaining language assessments all showed non-signiŽ cant diVerences, although it is worth noting that for the TROG the pattern was reversed and
for the Bus Story high scorers had a median score which fell in the normal range
( > 16 centiles), whilst low scorers fell below this threshold on average. Raven’s
Coloured Matrices (Raven 1986) given as a test of non-verbal cognitive ability at
7 years were not signiŽ cantly diVerent.
Change from 7 to 11 years was also possible to assess in three areas: TROG,
single-word reading and expressive vocabulary. The TROG was used at both stages
giving the most comparable results. For this analysis, centile scores for age at 7
years were subtracted from centile scores at age 11. A positive value represents
‘catch-up’, whilst a negative value represents a fall in performance for age. The high
scorers were found to score a median diVerence of 22.5 (a ‘catch up’ of over 1 SD)
whilst the low scorers scored a median change of Õ 9.75 (a relative drop in
performance; p 5 0.04). For single-word reading, children were assessed at 7 years
using the BAS single-word reading subtest and at 11 years using WORD as described
previously. Both tests involve reading a sequence of single words aloud and give
performance in centiles for age. A change analysis was completed as for the TROG.
High scorers showed a median change of 25.5 centiles whilst low scorers showed
a median diVerence of Õ 2.5 centiles ( p 5 0.001). Finally, expressive vocabulary was
assessed using BAS naming vocabulary at 7 years and using the EVT as described
previously at 11 years. A change analysis showed a diVerent pattern with high and
low scorers showing a similar fall in performance for age from 7 to 11 years (Õ 11.5
and Õ 9.5 respectively, p 5 0.87).
Discussion
The results from this study are interesting and thought provoking. The Ž ndings
clearly indicate a relationship between performance on a non-word task and actual
language ability. Interestingly, vocabulary measures were not as clearly associated
with non-word repetition at 11 or 7 years or in terms of progression of ability.
This may be partly due to the age of participants (11 years old) who would be
expected to score relatively well on this type of assessment (although note that this
sample had generally poor scores on expressive vocabulary with a whole group
median of 13th centile for age) and due to the diVerent assessment used at 11 years
which oVers a more in depth assessment of vocabulary knowledge.
In contrast, measures of grammatical ability such as the past tense task, third
person singular task and TROG, showed signiŽ cantly diVerent levels of performance
according to non-word skill group. This association was also translated into diVerences in the progress made by children in the area of receptive grammar from 7 to
11 years. This suggests that verbal ability is closely interwoven with verbal shortterm memory, not simply in terms of phonological output, but in terms of the
development of more complex language skill. This is supported by other research
such as that by Leonard et al. (2000) who found that priming eVects were evident
in a group of preschool children with SLI to a greater degree than their peers. In
their study, the children with SLI were more likely to make use of grammatical
morphemes if the preceding sentence contained target elements of syntax.
Nicola Botting and Gina Conti-Ramsden
428
Montgomery (2000) also found a signiŽ cant correlation between working memory
and sentence comprehension in groups with both SLI and normal development.
Furthermore, the groups in the present investigation were matched very closely for
non-verbal or performance IQ, thus taking into account any general cognitive
diYculties which may have lead to or been caused by the phonological impairments.
The Digit Span subtest from the verbal section of the WISC assessment was
signiŽ cantly associated with non-word repetition score (as seen in the diVerences
between groups), and this seems a plausible relationship given that both tasks have
a serial memory loading and a verbal element. Certainly Ž ndings from this study
conŽ rm a dissociation between general cognitive ability and speciŽ c memory tasks
as evidenced by the diVerences despite matching of performance IQ at 11 years
and the lack of diVerence in retrospective non-verbal ability scores assessed at
7 years.
Nature of memory deŽ cits in SLI
This study did not incorporate any non-verbal serial memory tasks, and other
studies seem to report diVering results as to whether diYculties are only in the
verbal domain. For example, Williams et al. (2000) found that whilst hyperactivity
was related to reduced spatial memory spans, this was not a characteristic of
language impairment. Nation et al. (1999) also found that their children with poor
reading comprehension had intact spatial memory spans. Farmer (2000) reported a
lack of association between memory deŽ cits and social cognition. Fazio (1997, 1998,
1999) has conducted a series of experiments showing that children with SLI have
diYculty remembering text such as nursery rhymes and poems, but found that
accompanying hand actions (i.e. a non-verbal sequence) signiŽ cantly improved
performance (1997) suggesting an unimpaired ability to remember non-verbal
sequences. However, Fazio (1999) also found poor performance on timed mathematical calculations and recall of maths facts in the same children a few years later.
Fazio reported a serial memory deŽ cit across tasks that did not require phonological
recoding (scribble patterns and unfamiliar faces) as well as for items that were likely
to be represented in this way (common objects). In this last study, she found instead
a strong association with the duration of item presentation rather than with the
type of image (Fazio 1998). Further to this, Edwards and Lahey (1998) hypothesized
from their data, that children with SLI have diYculties with the nature of phonological representations rather than the ability to hold phonological information in
working memory. This may explain why the groups in the present study were able
to diVer so drastically on non-word repetition whilst being so closely matched for
performance on non-verbal working memory tasks.
Literacy outcomes
This study also reaYrmed the association between phonological processing and
reading skill. This relationship was not only found cross-sectionally, but also regarding retrospective longitudinal data (scores at 7 years) and developmental data (change
from 7 to 11 years). Snowling et al. (2000) reported a close relationship between
the two in a group of adolescents who had been identiŽ ed as having a language
impairment as preschoolers and in control subjects. They also reported that children with preschool language diYculties were at greater risk of dyslexia (whilst
Non-word repetition and SLI
429
emphasizing that the two disorders develop diVerently). Interestingly, however, they
found that a small subgroup with isolated phonological impairments at preschool
age were not signiŽ cantly impaired on literacy measures, although they scored nearly
10 standard points lower than controls on the reading comprehension task and this
statistical non-signiŽ cance may well have been due to sample size. The current
study supports the possible link between non-word repetition and reading comprehension and conŽ rms the Ž nding of Nation et al. (1999) of an association not just
between phonological memory and decoding skills, but also between this factor
and reading comprehension ability. Gillam and Carlile (1997) also reported that
story retellings (from written text known to be above the children’s reading level),
were more confusing and less complete in children with SLI than in peers matched
for single-word reading ability. The authors suggest that impaired working memory
may be one factor underlying these results.
Verbal short-term memory and other impairments
It is important to underline that impairments in short-term verbal memory have
also been noted in other populations with impairments such as Down’s syndrome
( Jarrold et al. 1998) and in those with more complex communication diYculties
such as autism (Kjelgaard and Tager-Flusberg 2001). Cohen et al. (2000) found that
non-word repetition and sentence repetition tasks diVerentiated between patients
at a psychiatric clinic who had or did not have additional language impairments.
Acquired language diYculties such as those seen in Landau–KleVner syndrome also
appear associated with phonological short-term memory deŽ cits (Metz-Lutz et al.
2000) as do adverse developmental conditions such as being born with very low
birth weight (Briscoe et al. 1998). Thus, non-word repetition tasks appear to re ect
language ability in populations other than those with SLIs.
Memory tasks as a diagnostic marker
The identiŽ cation of a positive diagnostic marker for SLI would represent an
important step forward in terms of clinical eYcacy and also for genetic research.
Research by Stothard et al. (1998), Edwards and Lahey (1998) and Farmer (2000)
are supported by the Ž nding in our own research that non-word repetition is related
to actual language ability, but can the test identify individuals whose language
abilities have improved over time and now appear typical? That is, can non-word
repetition be used to identify subclinical impairments. The work of Bishop et al.
(1996, 1999) suggests that non-word repetition does have high heritability and is a
good predictor of language test scores. In addition, an examination of diVerent
psycholinguistic markers for SLI, Conti-Ramsden et al. (2001c) found that tasks
involving short term-memory (non-word repetition and sentence recall) were superior to those assessing syntactic skills at identifying groups of children with a history
of SLI at a younger age, even when language skills had improved. The study also
found that sentence recall, which very likely combines short-term memory and
linguistic knowledge, gave the most accurate results in this respect.
High scoring children with SLI: other considerations
It is an interesting fact in itself that we were able to Ž nd a group of children with
SLI who were high scoring on a non-word repetition task. First, it is worth
Nicola Botting and Gina Conti-Ramsden
430
highlighting how small in number this group were, i.e. 14/242 (6%). Second, their
existence may be because, in parallel with its relationship to language ability,
phonological short-term memory is associated with other factors not directly
assessed as part of this study. It has been reported for example that phonological
impairment responds particularly well to early specialist treatment programmes (Law
et al. 1998). No data exists as to whether our high-scorers received particularly
intensive, early or appropriate treatment in this respect. Furthermore, children with
diYculties that fall outside the typical range of impairments seen in SLI, such as
those with marked pragmatic language impairment (Botting and Conti-Ramsden
1999), may have a diVerent memory proŽ le. Indeed, when we subsequently examined
presence of pragmatic impairments in our sample, nine of the 14 high scorers and
only two of the low scorers were felt by teachers to have diYculties of this kind
even at 7 years of age ( Fisher’s exact p < 0.001). However, there was no signiŽ cant
diVerence on the number of children in each group falling below the threshold for
pragmatic diYculties on the Children’s Communication Checklist (Bishop 1998).
Nevertheless, this is an important consideration when examining clinical groupings
and further research is needed to establish whether children with pragmatic diYculties have the same pattern of underlying limitations as those with SLI.
Concluding remarks
Current research is increasingly suggesting that a strong short-term memory element
underlies language impairment. The present study conŽ rms this position and shows
that tests of phonological memory can be used to predict test performance in a
number of diVerent language domains as well as literacy performance. The Ž ndings
discussed here have serious implications for the educational progress of children
with SLI, especially the use of timed and/or oral testing conditions such as those
evident in some aspects of the UK School Achievement Tests (SATs; ContiRamsden et al. 2001b). In addition, this paper shows that the progress made by
children with high non-word repetition scores is signiŽ cantly greater than for those
with poor repetition scores. Although it is far from clear whether this association
is causal, this Ž nding has clinical implications in terms of therapy aims and priorities
since children with poor non-word repetition scores may require more intensive or
earlier therapy compared with high-scoring peers with SLI and therapeutic aims
may diVer.
Further work needs to be carried out to establish: (1) whether these diYculties
are more pronounced in children with SLI than in peers with other disorders, i.e.
whether tests such as non-word repetition can be used diagnostically for SLI or for
a wider description of any language impairment even when combined with other
diYculties; (2) whether short-term memory deŽ cits in children with SLI are purely
verbal or whether they ever occur in spatial/non-verbal tasks; and (3) which speciŽ c
tests of memory provide the most accurate tools for clinical screening and genetic
research. No doubt future research in SLI will address these important questions.
Acknowledgements
The authors gratefully acknowledge the NuYeld Foundation (Grant DIR/28) for
their continued Ž nancial support. They also thank Zoë Simkin and Emma Knox
Non-word repetition and SLI
431
for help with the data collection, and the schools and families who helped them
with this research.
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