State-of-Science Review: Specific Language Impairment


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

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State-of-Science Review: Specific Language Impairment

  1. 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 OxfordThis review has been commissioned as part of the UK Government’s Foresightproject: Mental Capital and Mental Wellbeing. The views expressed do not representthe policy of any Government or organisation. Page 1
  2. 2. Specific Language ImpairmentAbstract 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.” Page 2
  3. 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 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” ( 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 Page 3
  4. 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 Page 4
  5. 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 Page 5
  6. 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 Page 6
  7. 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 Page 7
  8. 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. Page 8
  9. 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.ReferencesBird, J., Bishop, D. V. M., & Freeman, N. (1995). Phonological awareness andliteracy development in children with expressive phonological impairments.Journal of Speech and Hearing Research, 38, 446-462.Bishop, D. V. M. (2006). What causes specific language impairment inchildren? Current Directions in Psychological Science, 15, 217-221.Catts, H. W., Fey, M. E., Tomblin, J. B., & Zhang, X. (2002). A longitudinalinvestigation of reading outcomes in children with languageimpairments. Journal of Speech, Language and Hearing Research, 45,1142-1157.Clegg, J., Hollis, C., Mawhood, L., & Rutter, M. (2005). Developmentallanguage disorders - a follow-up in later adult life. Cognitive, languageand psychosocial outcomes. Journal of Child Psychology andPsychiatry, 46, 128-149.Cohen, N. J. (2001). Language impairment and psychopathology in infants,children and adolescents. Thousand Oaks, CA: Sage.Cohen, N. J., Barwick, M. A., Horodezky, N. B., Vallance, D. D., & Im, N.(1998). Language, achievement, and cognitive processing in psychiatricallydisturbed children with previously identified and unsuspected languageimpairments. Journal of Child Psychology and Psychiatry, 39, 865-877.Cohen, W., Hodson, A., OHare, A., Boyle, J., Durrani, T., McCartney, E.,Mattey, M., Naftalin, L., & Watson, J. (2005). Effects of computer-basedintervention using acoustically modified speech (Fast ForWord-Language) in receptive language impairment: Outcomes from arandomised controlled trial. Journal of Speech, Language and HearingResearch, 48, 715-729.Conti-Ramsden, G., & Botting, N. (2004). Social difficulties and victimization inchildren with SLI at 11 years of age. Journal of Speech, Language, andHearing Research, 47, 145-161.Law, J., Garrett, Z., & Nye, C. (2004). The efficacy of treatment forchildren with developmental speech and language delay/disorder: ameta-analysis. Journal of Speech, Language, and Hearing Research, 47,924-943. Page 9
  10. 10. Leonard, L. B. (2000). Specific language impairment across languages. In D.V. M. Bishop & L. B. Leonard (Eds.), Speech and Language Impairments inChildren: Causes, Characteristics, Intervention and Outcome. Hove, UK:Psychology Press.Lundberg, I., & Linnakylä, P. (1993). Teaching reading around the world. IEAstudy of reading literacy. Technical report: International Association for theEvaluation of Educational Achievement.Paul, R. (2000). Predicting outcomes of early expressive language delay:Ethical implications. In D. V. M. Bishop & L. B. Leonard (Eds.), Speechand Language Impairments in Children: Causes, Characteristics,Intervention and Outcome (pp. 195-209). Hove, UK: Psychology Press.Roberts, J. E., Rosenfeld, R. M., & Zeisel, S. A. (2004). Otitis media andspeech and language: A meta-analysis of prospective studies. Pediatrics, 113,e238-248.Rouse, C., & Krueger, A. (2004). Putting computerized instruction to the test:a randomized evalutaion of a scientifically based reading program.Economics of Education Review, 23, 323-338.Schiff-Myers, N. (1988). Hearing children of deaf parents. In D. Bishop & K.Mogford (Eds.), Language development in exceptional circumstances (pp. 47-61). Edinburgh: Churchill Livingstone.Simkin, Z., & Conti-Ramsden, G. (2006). Evidence of reading difficulty insubgroups of children with specific language impairment. Child LanguageTeaching and Therapy, 22, 315-331.Snowling, M. J., Adams, J. W., Bishop, D. V. M., & Stothard, S. E. (2001).Educational attainments of school-leavers with a pre-school history ofspeech-language impairments. International Journal of Language andCommunication Disorders, 36, 173-183.Snowling, M. J., Bishop, D. V. M., Stothard, S. E., Chipchase, B., &Kaplan, C. (2006). Psychosocial outcomes at 15 years of children with apreschool history of speech-language impairment. Journal of ChildPsychology and Psychiatry, 47, 759-765.Stevenson, P., Bax, M., & Stevenson, J. (1982). The evaluation of homebased speech therapy for language delayed pre-school children in an innercity area. British Journal of Disorders of Communication, 17, 141-148.Stothard, S. E., Snowling, M. J., Bishop, D. V. M., Chipchase, B. B., &Kaplan, C. A. (1998). Language impaired preschoolers: A follow-up intoadolescence. Journal of Speech, Language and Hearing Research, 41,407-418. Page 10
  11. 11. Tallal, P., Miller, S. L., Bedi, G., Byma, G., Wang, X., Najarajan, S. S.,Schreiner, C., Jenkins, W. M., & Merzenich, M. M. (1996). Languagecomprehension in language-learning impaired children improved withacoustically modified speech. Science, 271, 81-84.Tomblin, J. B., Records, N. L., Buckwalter, P., Zhang, X., Smith, E., &OBrien, M. (1997). Prevalence of specific language impairment inkindergarten children. Journal of Speech, Language, and HearingResearch, 40, 1245-1260.Troia, G. A., & Whitney, S.D. (2003). A close look at the efficacy of FastForWord Language for children with academic weaknesses. ContemporaryEducational Psychology, 28, 465-494.Zhang, X., & Tomblin, J. B. (2000). The association of intervention receipt withspeech-language profiles and social-demographic variables. AmericanJournal of Speech-Language Pathology, 9, 345-357. Page 11