Review commissioned as part of the UK Government’s Foresight Project, Mental Capital and Wellbeing, 2008

1. DRAFT
Foresight – SR-D1 v1 stage 2
Mental Capital and Mental Wellbeing
Office of Science and Innovation
Version date: 27th April 2007
State-of-Science Review:
Specific Language Impairment
Professor Dorothy Bishop
Department of Experimental Psychology,
University of Oxford
This review has been commissioned as part of the UK Government’s Foresight
project: Mental Capital and Mental Wellbeing. The views expressed do not represent
the policy of any Government or organisation.
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2. Specific Language Impairment
Abstract
 What is Specific Language Impairment (SLI)? Brief account of criteria
used
 What causes SLI? Evidence for strong genetic component. Popular
belief that poor language input from parents causes SLI is not
supported by research evidence.
 How common is SLI? Will depend on cut-offs used. Clinically significant
problems decline markedly with age
 International comparisons. Difficult because of lack of comparable
language measures, and differences in organisation of services.
 Educational impact of SLI. High risk of poor literacy and educational
failure in those whose SLI persists to 5 years or beyond.
 Impact of SLI on the individual and society. High rates of
unemployment, social isolation and psychiatric disorder.
 Can we predict outcome? Age, severity and level of comprehension as
important predictors.
 Can we intervene effectively? Woeful lack of good evidence, especially
for older children. Many have persisting difficulties into adulthood
despite intensive intervention. Computerised intervention worth
exploring but has not so far fulfilled early promise.
 Future trends. Prevalence likely to be stable. Emphasis on early years
intervention only cost-effective if we identify those whose problems are
likely to persist. Need for controlled trials of intervention. Need for
proactive approach to identifying niches in society for people who lack
language skills.
What is Specific Language Impairment (SLI)?
 SLI is diagnosed when a child’s language fails to develop along normal
lines for no obvious reason: hearing loss, physical disability, emotional
disturbance, parental neglect and brain injury are all ruled out before
the diagnosis is made. The child is developing normally in areas other
than language, and will show adequate intelligence if tested using
nonverbal measures (e.g. construction puzzles; reasoning tasks with
shapes).
 Most people have heard of dyslexia and autism, but not SLI. This
illustrates the power of labels: SLI is far more common than autism,
and has close commonalities with dyslexia, but it does not have a
catchy medical-sounding label, so it is neglected.
 The manifestations of SLI are variable both in terms of severity and
quality: in some children, the main difficulties are a delay in starting to
talk, with immature language persisting into school age. For other
children, problems in understanding language predominate: they may
take in only one or two words of a complex sentence such as “if you
bring your swimsuit tomorrow, we can go to the pool after lunch.”
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3. Vocabulary is usually limited in SLI, and children may have problems
understanding unusual or abstract terms.
 It is likely that the term SLI is an umbrella term for a range of distinct
disorders, but as yet there is no agreement about subtypes.
 A brief film featuring two young people with speech and language
problems, Stephen and Graham, can be found on
http://www.ican.org.uk/
What causes SLI?
 30 years ago, it was often assumed that SLI was the consequence of
poor parenting. This view was reinforced as recently as 2003 in a
speech by Alan Wells, Director of the Basic Skills Agency, who
maintained that many families do not converse with their children, and
use instead a "daily grunt”
(http://news.bbc.co.uk/1/hi/education/2638889.stm). In fact, language
development in children appears remarkably resilient in the face of
limited language input: perhaps the clearest evidence comes from
normally-hearing children who are raised by parents who are
profoundly deaf and unable to converse intelligibly. In most cases,
these children learn to talk normally, provided they are exposed to a
small amount of normal language (Schiff-Myers, 1988).
 Although other factors, such as chronic middle ear disease (which
causes a mild and fluctuating hearing loss) may play a role in SLI, it is
now generally accepted that this condition is not usually associated
with hearing difficulties (Roberts et al., 2004), and is a strongly genetic
disorder (Bishop, 2006). The best evidence comes from studies of
twins. Two twins growing up together are exposed to the same home
environment, yet may differ radically in their language skills. Such
different outcomes are, however, seen almost exclusively in fraternal
(non-identical) twins, who are genetically different. Identical twins share
the same genes and tend to be much more similar in language ability.
There can be some variation in the severity and persistence of SLI in
identical twins, indicating that environmental factors affect the course of
disorder, but it is unusual to find a child with SLI who has an identical
twin with normal language.
 Although twin studies indicate genes are important, SLI is not usually
caused by a mutation in a single gene. Current evidence suggests that
there are many different genes that can influence language learning,
and SLI results when a child inherits a particularly detrimental
combination of risk factors (Bishop, 2006).
 Parents of children with SLI have similar genetic makeup and may well
have limited language skills themselves. We need to beware of
assuming that a parent with poor language has caused their child’s
problems because of lack of stimulation.
How common is SLI?
 There is no sharp dividing line between SLI and normality: children vary
in their language abilities, and the frequency of SLI will therefore
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4. depend on how stringently it is defined. An epidemiological study in the
US identified around 7.4% of 5-year-olds as having SLI (Tomblin et al.,
1997), based on an initial screening test followed by a more detailed
language assessment, but they noted that this figure could rise or fall
depending on the cutoffs used to define impairment.
 An alternative way of estimating the scale of the problem is to consider
the proportion of children referred for speech and language therapy:
however, this does not give a satisfactory prevalence estimate,
because it will depend on resources. Furthermore, problems with
speech production and expressive language are more readily identified
than poor language comprehension, but the latter has a worse
prognosis (Zhang & Tomblin, 2000). In the study by Tomblin et al.
(1997), in only 29% of cases had parents been informed previously that
the child had speech and language problems.
 The media occasionally run stories about an “epidemic” of language
impairment in children starting school, sometimes attributing it to
working parents, TV, and so on. There is no hard evidence of any
secular change in prevalence of language difficulties. It is likely that
perception of problems is inflated by the fact that more children are
starting school at 4 years of age, and our large cities now include
unprecedented numbers of children who do not have English as a first
language. It would be well worth instituting an epidemiological study to
monitor rates of language impairment (and related disorders), every 10
years or so, using standard methods of assessment, to estimate the
true scale of the problem, and identify any secular trends.
International comparisons
 It is not possible to compare SLI in the UK with other countries. Part of
the problem is that language assessments used to identify SLI may not
work in translation, and can only be interpreted if we have adequate
norms (i.e., data on a large representative population of children, that
allow us to quantify typical performance at different ages). In many
countries such data do not exist. Furthermore, even in English-
speaking countries, there are difficulties in making international
comparisons, because tests may be culturally specific.
 There is a fascinating research literature comparing manifestations of
SLI in different languages, but this is primarily of interest to those
working on theoretical conceptualisations of the disorder (Leonard,
2000).
Educational impact of SLI
 Numerous studies have demonstrated that children with SLI are at high
risk of educational failure. Low levels of literacy are common, even in
children who receive specialist help, and educational attainments are
typically poor (e.g. Catts et al., 2002; Snowling et al., 2001). This bleak
picture is especially applicable to children who have language
impairments that persist beyond the age of 5 years, and where
comprehension as well as expressive language is affected. For
instance, Simkin and Conti-Ramsden (2006) found that 67% of children
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5. with expressive SLI and 88% of those with receptive SLI had serious
reading difficulties at 11 years of age.
Impact of SLI on the individual and society
 SLI is associated with a high rate of psychiatric disorder (see review by
Cohen, 2001). For instance, Conti-Ramsden and Botting (2004) found
that 64% of a sample of 11-year-olds with SLI scored above a clinical
threshold on a questionnaire for psychiatric difficulties, and 36% were
regularly bullied, compared with 12% of comparison children. The
greatest risk appears to be for attentional problems and social
difficulties, rather than conduct or emotional disorders. Looked at from
the other direction, a study of children attending psychiatric clinics
found that 28% had hitherto undetected language difficulties that were
moderate or severe (Cohen et al., 1998). The reason for this
association is not fully understood. An obvious mechanism is via stress
induced by social rejection and isolation, both of which are common in
children with language difficulties. In addition, a child with poor
language skills may fail to use internalised language as a method of
self-regulation, e.g. talking oneself through past events or future plans,
or instructing oneself to behave in a particular way. It is also possible
that the same genes that influence language learning lead directly to
psychiatric vulnerability.
 There are a few studies of the long-term outcome of children with SLI,
and they mostly make depressing reading. There are elevated rates of
unemployment, social isolation and psychiatric disorder (Clegg et al.,
2005). However, most studies focused on outcomes of those with
severe problems, where comprehension as well as expressive
language is affected. Better outcomes were seen for children who had
milder difficulties and did not require special educational provision
(Snowling, et al., 2006). Where language difficulties had resolved by 5
years of age, there was no excess psychopathology.
Can we predict outcome?
 Longitudinal studies of young children with SLI generally agree that
long-term outcome is worse in those who have more severe problems
(e.g. Stothard et al.,1998). Severity can be measured both in terms of
the level of performance on a given language measure, and the range
of language functions that are affected.
 Age is also critical. Understandably, there is much interest in identifying
children as young as possible, on the grounds that early intervention is
likely to be more effective than late. However, the situation is
complicated by the fact that many children make good spontaneous
progress after a late start in language. There have been several studies
of ‘late-talkers’, identified at age 18-24 months because they are
producing very few words. Most such children appear to be late
bloomers, in that their outcome is similar to that of other children when
followed up into middle childhood (Paul, 2000). A key factor appears to
be comprehension level: those who have poor understanding of what
others say are less likely to spontaneously catch up. However, the
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6. evidence base for this claim is slender, as few studies have looked
specifically at comprehension in young children.
 One can also see spontaneous recovery between 4 and 5 years of age,
especially in children whose problems are predominantly with
expressive language. One UK study studied children who had specific
speech and language problems at 4 years of age; they were seen at
4.5 yr, 5.5 yr, 8 yr and 15 yr. Around 40% had essentially normalised
by 5.5 years, and their long-term outcome was generally good,
although minor literacy problems were found in some (Stothard et al,
1998). However, the 60% who still had measurable language problems
at 5.5 years fared much worse, with the gap between them and other
children widening as time went by. For the most severely affected
children, it was not uncommon to see a drop in nonverbal intelligence
in adolescence, as well as stagnation of language skills.
Can we intervene effectively?
 It would be a mistake to imagine that findings on genetics of SLI
preclude the development of effective interventions. What the genetics
studies tell us is that the kinds of variations in environment that most
children experience do not play a salient role in determining who has a
language problem. Thus, simply talking more to these children is
unlikely to improve their language skills. But the genetic findings do not
preclude the development of interventions tailored specifically to the
child’s problems that could be effective. By analogy, we know that
diabetes has a genetic basis, but we do not conclude the condition is
untreatable: rather, we devise treatments that are outside the normal
range of experience to tackle the underlying cause.
 Children with SLI will normally receive therapy from a Speech and
Language Therapist (SALT). In more severe cases, the child may
receive special educational provision, either in a specialist class in a
mainstream school, or in a special school.
 Unfortunately, there has been little research on efficacy of interventions
for SLI (Law et al, 2004). Such evidence as exists suggests
intervention can be effective for improving intelligibility in children with
speech impairments, but there is a lack of good research on
interventions for language impairments, particularly with older children.
In the UK, there are a number of special schools that have developed
skills in working with older children with SLI over many years, but this
knowledge is fragmented and not widely available, and there are no
well-controlled studies of efficacy.
 One problem for intervention studies is that one is often looking for an
effect of intervention that may be superimposed on spontaneous
improvement. SALTs regard early intervention as important, and some
local authorities focus all their resources on preschoolers, and have no
provision for school-aged children. This strategy is no doubt reinforced
by the fact that many preschoolers who receive therapy make excellent
progress. The point that is often missed is that many of these children
would have done well with no intervention. For example, in one
controlled study of early intervention there was no difference between
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7. treated and untreated children, not because nobody improved, but
because everyone improved (Stevenson et al., 1982). Clearly we do
not want to wait to intervene with those children who are at risk for
long-term problems, but it is important to use research evidence on
predictors to focus intervention those children who are unlikely to
improve spontaneously.
 One relatively new advance has been development of computerised
interventions for SLI. The best-known of these is FastForword® (FFW),
which was developed out of research showing that children with SLI
have problems in processing sounds that are brief or rapid (Tallal et al.,
1996). The idea behind FFW is that the brain can be trained to
perceive increasingly small differences between sounds. Children play
computerised games that adjust the level of difficulty of discrimination
to the child’s performance level. The games involve both language
stimuli (e.g. child determines whether a spoken sentence matches a
pictured scenario) and nonlinguistic sounds (e.g. glides that resemble
animal sounds, and vary in speed of change). The originators of FFW
have won scientific accolades for what appeared at first to be a
researcher’s Holy Grail – an intervention developed out of basic
neuroscience that would help children. Unfortunately, later evaluations
have found that FFW has not fulfilled its early promise, and appears to
do no better than conventional speech and language therapy (e.g.,
Cohen et al., 2005). This is surprising, given that the intervention is so
intensive, requiring the child to spend 90-100 minutes per day on the
program for around 6 weeks. Although school boards in the US have
bought into the program (in some cases for all pupils, not just those
with SLI), there is growing scepticism as to whether this is justified,
given the high financial cost of the program, and the time the child has
to spend away from regular school activities (Troia & Whitney, 2003).
An editorial in Nature Neuroscience (January 2004) expressed concern
that this kind of educational program is being marketed without the
evidence for efficacy that would be required for a drug treatment.
 A final point to stress about early intervention concerns the link
between SLI and poor literacy. Children in UK schools are introduced
to literacy at ever earlier ages. In this regard, the UK is very different
from our European neighbours, where children are often not introduced
to literacy until 6 or even 7 years of age; rather, they education focuses
on language-based activities that build the skills needed for successful
reading and writing. The available evidence suggests that this late start
does not lead to literacy problems, though comparisons are
complicated by the different orthographies of different languages
(Lundberg & Linnakylä, 1993). Evidence from children with SLI
suggests that those who fail in literacy are children who are exposed to
literacy instruction when relevant linguistic skills are still
underdeveloped (Bird et al., 1995). It is possible that children would do
better if literacy instruction were delayed until they had been shown to
have a critical level of linguistic skill.
 Ideally we need studies of efficacy that adopt the methods of
randomised controlled trials as used in mainstream medicine. These
are expensive and can run into difficulty because of the reluctance of
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8. many SALTs to have an untreated control group. They argue this is
unethical; however, it could equally be argued that that it is unethical to
persist in using interventions of unproven efficacy, especially when
resources are limited. Unfortunately, it is impossible to do a cost-
effectiveness analysis of interventions for SLI because we lack
information on efficacy, both for improving SLI and for preventing other
adverse outcomes.
Future trends
 The prevalence of SLI is likely to remain stable over the years, but its
impact could become more serious, as our society becomes
increasingly dependent on literacy skills.
 Intervention currently focuses on the early years – from as early as 18
months in some cases, and up to around 4 years of age. This focus,
though understandable, may be non-optimal, because of high levels of
spontaneous improvement. One way forward would be to combine
early intervention with use of using predictors from test results to
identify those whose problems are unlikely to resolve spontaneously.
 It would be worth conducting a controlled trial to consider whether
children’s literacy skills can be enhanced by deferring literacy training
until a minimal level of language competence has been attained.
 Computerised intervention has generated great excitement, because it
has the potential to deliver thousands of events to a child in a game-
like format, thereby maintaining motivation, and adapting on-line to the
child’s responses. Although attempts to develop computerised
programs for treating SLI have, as yet, not been shown to be effective,
we have as yet barely explored the potential of this approach. More
research is needed to identify the conditions under which children with
SLI can learn most effectively.
 We should not underestimate the difficulty of remediating SLI: we may
need to accept that some children will never be competent
communicators. If so, then putting all our efforts into working to improve
their language skills may be as futile as trying to train a blind child to
see. For many children, education can be a dispiriting experience
characterised by continual failure. We should continue to do research
to identify barriers to language learning in these children so we can
develop more effective interventions, but this should not be at the
expense of other areas of development. It would be desirable to identify
for a child with SLI a non-linguistic skill in which they could succeed,
and to devote time on the curriculum to fostering this. These children
could also benefit from prophylactic intervention designed to avoid the
associated social problems: thus intervention with them would go
beyond the narrow remit of improving language skills, to work also to
enhance their ability to make friendships and find a role in the wider
world. The modern world is increasingly hostile to those who lack skills
in literacy, communication and computer processing: it may be
necessary to take a more proactive approach to identifying niches for
people who lack these skills.
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9.  Conventional speech and language therapy has evolved in response to
a clinical need, and is not an exact science. We need to ensure that
clinical skills that are developed in specialist centres are preserved and
disseminated. More use of video-links between specialist centres and
mainstream schools could be helpful. Specific educational methods
also need formal evaluation, so we can identify the most effective
approaches.
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literacy development in children with expressive phonological impairments.
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Bishop, D. V. M. (2006). What causes specific language impairment in
children? Current Directions in Psychological Science, 15, 217-221.
Catts, H. W., Fey, M. E., Tomblin, J. B., & Zhang, X. (2002). A longitudinal
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