Research ino dyslexia provision in Wales Lieraure review on he sae of research for children wih dyslexia PHOTO REDACTED DUE TO THIRD PARTY RIGHTS OR OTHER LEGAL ISSUES Research Research documen no: 058/2012 Dae of issue: 24 Augus 2012
Research ino dyslexia provision in Wales Audience Local auhoriies and schools. Overview The Welsh Governmen commissioned a lieraure review, audiing and benchmarking exercise o respond o he recommendaions of he former Enerprise and Learning Commiee s Follow-up repor on Suppor for People wih Dyslexia in Wales (2009). This work was conduced by a working group, which comprised of expers in he field of specific learning difficulies (SpLD) in Wales including he Cenre for Child Developmen a Swansea Universiy, he Miles Dyslexia Cenre a Bangor Universiy, he Dyscovery Cenre a he Universiy of Wales, Newpor, he Wrexham NHS Trus and represenaives from he Naional Associaion of Principal Educaional Psychologiss (NAPEP) and he Associaion of Direcors of Educaion in Wales (ADEW). Acion required None for informaion only. Furher informaion Enquiries abou his documen should be direced o: Addiional Needs Branch Suppor for Learners Division Deparmen for Educaion and Skills Welsh Governmen Cahays Park Cardiff CF10 3NQ Tel: 029 2082 6044 Fax: 029 2080 1044 e-mail: AddiionalLearningNeedsBranch@wales.gsi.gov.uk Addiional copies This documen can be accessed from he Welsh Governmen s websie a hp://wales.gov.uk/opics/educaionandskills/publicaions/ researchandevaluaion/research/?lang=en Relaed Curren lieracy and dyslexia provision in Wales: A repor on he documens benchmarking sudy (2012) Digial ISBN 978 0 7504 7972 1 Crown copyrigh 2012 WG16498
Conens ACKNOWLEDGEMENTS 2 I. INTRODUCTION 3 II. CURRENT DEFINITIONS OF DYSLEXIA 4 III. MAIN THEORETICAL ACCOUNTS AND ASSOCIATED EVIDENCE 7 IV. CROSS LINGUISTIC FACTORS IN THE EXPRESSION OF DYSLEXIA 18 V. DYSLEXIA AND OVERLAPPING DISORDERS 21 VI. PSYCHOSOCIAL OUTCOMES 29 VII. SCREENING 31 VIII. ASSESSMENT OF DYSLEXIA 33 IX. INTERVENTIONS CURRENTLY ACCEPTED AS BEST PRACTICE 35 X. COMPLEMENTARY INTERVENTIONS 41 XI. LOOKING TO THE FUTURE 46 REFERENCES 49 APPENDIX A 91 Table A1 92 Table A2 93 Table A3 93 Table A4 94 Table A5 95 Table A6 96 Inervenions 102 Table A7 103 Table A8 109 Table A9 111
2 ACKNOWLEDGEMENTS This Lieraure Review was led and edied by Markéa Caravolas (Senior Lecurer in Psychology and Direcor of he Miles Dyslexia Cenre, Bangor Universiy) in collaboraion wih Amanda Kirby (Professor of Educaion and Direcor of he Dyscovery Cenre, Newpor Universiy), Angela Fawce (Professor and Direcor of he Cenre for Child Research, Swansea Universiy), and Kahleen Glendenning (Paediaric Physioherapis and Service Manager for Children wih Disabiliies, BCUHB Norh Wales NHS Trus). Many hanks go o Ms Andrea Reynolds (Bangor Universiy) and Ms Sarah Jackson (Newpor Universiy) for heir help wih he exensive lieraure searches, formaing and proofreading. Thanks also o Mrs Julie Benne (Bangor Universiy) for help wih general adminisraion of he projec.
3 I. INTRODUCTION The presen lieraure review was commissioned by Jane Hu, Welsh Assembly Miniser for Children, Educaion, Lifelong Learning and Skills, in response o he Enerprise and Learning Commiee s repor Suppor for People wih Dyslexia in Wales (2008) and he recommendaions herein. The lieraure review is o guide he Miniser (now Leighon Andrews) in he implemenaion of measures o promoe bes pracice in schools for he suppor of pupils wih dyslexia and oher relaed developmenal disorders. The lieraure review also provides a imely documen o inform he newly esablished Naional Lieracy Plan. The Enerprise and Learning Commiee s repor highlighed en key recommendaions for he beermen of suppor for dyslexic pupils in Welsh schools, including he agreemen of a definiion of dyslexia, effecive early idenificaion (screening and assessmen), effecive inervenion especially in early years, eacher raining on dyslexia, and provision in he Welsh language. This Lieraure Review was commissioned as par of he Miniser s response o hese recommendaions, wih a view o informing policy decisions abou he design and implemenaion of such provision. The Review is herefore necessarily very broad in is scope, ye our objecive was o capure succincly boh he seminal findings in each relevan research area, as well as o summarize he imporan new findings ha are shaping curren undersanding and developmens in dyslexia research and pracice. The Review was underaken wih he Welsh conex in mind, wih aenion o advances in dyslexia wihin bilingual learning seings. The Review consiss of wo main documens: (1) he Lieraure Review, which includes he references and appended Tables, and (2) an Annoaed Bibliography. The firs documen, he Review, is presened in 11 chapers which include he Inroducion (Ch. I); an overview of curren definiions of dyslexia (Ch. II); an overview of he main heoreical and empirical accouns of he causes of dyslexia (Ch.III); an overview of curren knowledge of he manifesaion of dyslexia in differen languages and in bilingual individuals (Ch. IV); a review of research ino developmenal disorders ha may co occur wih dyslexia (Ch. V); a review of he longer erm educaional and psychosocial oucomes of individuals wih dyslexia (Ch. VI); an overview of issues associaed wih screening (Ch. VII) and assessmen (Ch. VIII) of dyslexia; a review of he raionale and effeciveness of lieracy inervenion approaches currenly held o reflec bes pracice (Ch. IX); and a review of some commercially available complemenary inervenion approaches (Ch. X); we conclude wih a consideraion of he implicaions for bes pracice in supporing children wih dyslexia and oher SpLDs in Welsh schools, and wih a noe on developing a revised definiion of dyslexia (Ch. XI). Throughou he Review, summary boxes are used o highligh key conceps and findings, while more deailed daa and maerials are presened in he Tables of Appendix A (his documen). The Reference secion conains all publicaions cied in he lieraure review as well as hose addiionally included in he Annoaed Bibliography (accompanying documen). The Annoaed Bibliography (Appendix B and C) is provided as a supplemenary documen, which conains a brief descripion of all of he research cied in he Lieraure Review, as well as a sample of addiional, represenaive research publicaions available in opic areas covered in he Review. The summaries are hemaically organized (e.g., Phonological Defici, Memory Defici, Cross linguisic Facors, ec.) and are ranked according o he mehodological rigour of he sudy. The crieria for our ranking sysem are provided in Appendix B. The summaries are srucured sysemaically and include (a) he full reference, and ile of each aricle, (b) a summary of he design, sample size, and saisical approach, (c) a summary of he key findings, and (d) commens of he reviewer, where relevan. In cases where hese annoaions were no provided, he published aricle absrac is provided insead.
4 II. CURRENT DEFINITIONS OF DYSLEXIA The definiion of dyslexia, is aeiology, and mos significan manifesaions are updaed and revised regularly as he ongoing research effor brings new knowledge and undersanding. Because he research is being carried ou by researchers in differen spheres, including educaion, psychology, biology, neuroscience, and medicine, he focus of a definiion can vary depending on he naure of he organizaion ha generaed i. Below, a selecion of curren definiions by he mos prominen naional and inernaional organizaions is provided. In addiion, in Appendix A, Table A1 conains a summary of he key similariies and differences among definiions of 11 organizaions and specialis bodies. The able allows he reader o see he bes esablished findings o dae on he behavioural markers of dyslexia. II.i Definiions of Key UK Bodies Briish Dyslexia Associaion (17 Ocober, 2007) Dyslexia is a specific learning difficuly, which mainly affecs he developmen of lieracy and language relaed skills. I is likely o be presen a birh and o be life long in is effecs. I is characerised by difficulies wih phonological processing, rapid naming, working memory, processing speed, and he auomaic developmen of skills ha may no mach up o an individual s oher cogniive abiliies. I ends o be resisan o convenional eaching mehods, bu is effecs can be miigaed by appropriaely specific inervenion, including he applicaion of informaion echnology and supporive counselling. Deparmen for Educaion and Skills (2004) We undersand dyslexia o be a specific difficuly, ypically characerised by an unusual balance of skills. Dyslexia affecs informaion processing (receiving, holding, rerieving and srucuring informaion) and he speed of processing informaion. I herefore has an impac on skills such as reading, wriing, using symbols and carrying ou calculaions. However, here are many differing definiions; dyslexia is an umbrella erm. I is imporan o recognise ha: dyslexia is no relaed o inelligence and can occur in severe, moderae, or mild forms people wih dyslexia have heir own individual profiles of srenghs and weaknesses; no wo people are exacly he same and he impac of dyslexia on each individual is differen dyslexia does no only affec lieracy skills such as spelling, bu mos of wha we know abou i relaes o is relaionship o language and lieracy dyslexia may overlap wih relaed condiions such as dyspraxia, aenion defici disorder (wih or wihou hyperaciviy) and dysphasia mos people appear o be born wih dyslexia, alhough ohers acquire i hrough acciden or illness many people wih dyslexia have a family member wih he same condiion some researchers hink ha dyslexia affecs more men han women; ohers hink ha roughly he same numbers of males as females are affeced. Rose Dyslexia Review 2009 Dyslexia is a learning difficuly ha primarily affecs he skills involved in accurae and fluen word reading and spelling. Characerisic feaures of dyslexia are: Difficulies in phonological awareness, verbal memory and verbal processing speed. Dyslexia occurs across he range of inellecual abiliies. I is bes hough of as a coninuum, no a disinc caegory, and here are no clear cu off poins. Co occurring difficulies may be seen in: aspecs of language, moor co ordinaion, menal calculaion, concenraion and personal organisaion, bu hese are no, by hemselves, markers of dyslexia.
5 A good indicaion of he severiy and persisence of dyslexic difficulies can be gained by examining how he individual responds or has responded o well founded inervenion. Dyslexia Scoland (Definiion produced by he Scoish Governmen in collaboraion wih a range of sakeholders including Dyslexia Scoland) Dyslexia can be described as a coninuum of difficulies in learning o read, wrie and/or spell, which persis despie he provision of appropriae learning opporuniies ha are effecive for he majoriy of learners. These difficulies may no be ypical of an individual's performance in oher areas. Ranging from mild o severe, here may be associaed difficulies in areas such as: audiory and /or visual processing of language based informaion; phonological awareness; oral language skills; shor erm and working memory; sequencing; number skills; organisaional abiliy. Moor skills and co ordinaion may also be affeced. Dyslexia exiss in all culures and across he range of abiliies and socio economic backgrounds. I is a life long condiion which is generally considered o be herediary. II.ii Definiions of Key Inernaional Bodies Inernaional Dyslexia Associaion (IDA) Dyslexia is a specific learning disabiliy ha is neurological in origin. I is characerized by difficulies wih accurae and/or fluen word recogniion and by poor spelling and decoding abiliies. These difficulies ypically resul from a defici in he phonological componen of language ha is ofen unexpeced in relaion o oher cogniive abiliies and he provision of effecive classroom insrucion. Secondary consequences may include problems in reading comprehension and reduced reading experience ha can impede he growh of vocabulary and background knowledge. (Adoped by he Board of Direcors: November 12, 2002.) Diagnosic and Saisical Manual of Menal Disorder Fourh Ediion Tex Revision 2005 (DSM IV TR) Reading Disorder Diagnosic Feaures. The essenial feaure of Reading Disorder is reading achievemen (i.e., reading accuracy, speed, or comprehension as measured by individually adminisered sandardized ess) ha falls subsanially below ha expeced given he individual s chronological age, measured inelligence, and ageappropriae educaion. Crierion A. The disurbance in reading significanly inerferes wih academic achievemen or wih aciviies of daily living ha require reading skills. Crierion B. If a sensory defici is presen, he reading difficulies are in excess of hose usually associaed wih i. Crierion C. If a neurological or oher general medical condiion or sensory defici is presen, i should be coded on Axis III. In individuals wih Reading Disorder (which has been called dyslexia ), oral reading is characerized by disorions, subsiuions, or omissions, boh oral and silen reading are characerized by slowness and errors in comprehension. Associaed Feaures and Disorders. Mahemaics Disorder and Disorder of Wrien Expression are commonly associaed wih Reading Disorder, and i is relaively rare for eiher of hese disorders o be found in he absence of Reading Disorder.
6 Overview of Dyslexia Definiions The majoriy of he definiions highlighed he fac ha dyslexia is a specific learning difficuly ha affecs lieracy skills. The definiions are mainly descripive and causaion is no addressed. However, where causaion is saed i is believed o be neurological in origin. A variey of deficis associaed wih he disorder is highlighed, he mos common of which include lieracy difficulies and phonological impairmens, and hese may range from mild o severe and are unique o each individual. The disorder is life long, however is effecs may be miigaed hrough he use of appropriae eaching mehods. The main discrepancies beween definiions involve inclusion of some of he behavioural manifesaions of he disorder, in paricular moor skills and coordinaion deficis and wheher inellecual abiliies can be used for diagnosis. Issues and New/Fuure Direcions in Defining Dyslexia The discrepancy definiion of dyslexia is being replaced by a dimensional definiion wih a core defici in phonological processes (Bishop, Snowling, & Blakemore, 2008). The BPS definiion focuses on a descripive and no a causal explanaion of dyslexia. Dyslexia is increasingly seen as a disorder ha may include more han one domain of impairmen. For example, dyslexia may resul from no only a phonological defici bu also oher cooccurring deficis in areas such as general language or visual aenion. Imporanly, he balance of curren evidence indicaes ha none of he deficis frequenly seen o co occur wih he phonological defici is sufficien o cause he disorder on is own. Fuure research will need o esablish he prevalence of pure phonological dyslexia, relaive o dyslexia wih comorbid or co occurring deficis, and o define clearly which addiional sympoms are direcly causal in dyslexia, and which coexis, and compound he dyslexic difficulies hrough indirec effecs.
7 III. MAIN THEORETICAL ACCOUNTS AND ASSOCIATED EVIDENCE Overview Dyslexia can be sudied from many differen perspecives, and here has been no shorage of heoreical proposals o explain he condiion of dyslexia over he pas cenury. In he secions ha follow, we summarize he heories ha have araced considerable aenion from researchers and we presen some represenaive research invesigaing he paricular heories. More deailed summaries of he lieraure are provided in he Annoaed Bibliography, annexed o he presen documen (Appendix C). The research summaries in he Annoaed Bibliography are ranked in erms of heir mehodological srengh, and we provide a descripion of hese crieria in he Appendix B. Alhough we do no adop one paricular heoreical perspecive in he presen review, we have aemped o selec he papers ha have me he mos rigorous sandards of scienific inquiry o represen each view. This said, he research base is no equally advanced for every heory; in cases where no consensus has ye been reached, and/or where he criical research has ye o be carried ou, we repor research ha reflecs he curren debae in he field. III.i Cogniive and Brain Bases of Dyslexia Recen research and research currenly in progress The heories are presened in he order in which hey have emerged, wih examples of ineresing recen research wihin each framework. There have been sriking developmens in dyslexia research in he las fifeen years, wih various heories hoping o fill in par of he jigsaw ha migh explain he complex problem of dyslexia, which can exend beyond lieracy difficulies and impac on an individual hroughou his/her life. The UK is a he forefron in his heoreical research, and an aspiraion of he scienific communiy is o advance boh he heoreical and empirical work so as o develop a comprehensive explanaion of he causes and manifesaions of dyslexia. In organizing his lieraure review, an imporan disincion beween he hree levels of heory proposed by Frih (1997) was considered: he biological, he cogniive and he behavioural levels. 1. The behavioural level examines he sympoms of dyslexia, such as poor reading, or phonological awareness deficis, and verbal memory difficulies. 2. A he cogniive level, heories propose o accoun for he causes of dyslexics observable difficulies on he basis of hypoheses abou srucural or funcional differences in he brain s informaion processing capaciies. For example, differen heoriss have proposed ha dyslexics pervasive reading and spelling deficis are caused by underlying problems in cogniive domains such as phonological processing, visual aenion, skill auomaisaion, and slow processing speed. 3. Finally, a he biological (i.e., brain and/or geneic) level lie he underlying brain mechanisms and he poenial deerminans of heir developmen. Differences beween he brains of dyslexic and nondyslexic individuals have been invesigaed in pars of he brain, including language areas, he fronal lobes, magnocellular pahways, and he cerebellum. Work is under way in behavioural geneics o idenify he genes ha may play a role in deermining hese brain and behavioural differences. I has been recognised ha any complee explanaion of dyslexia mus include all hree levels, wih he cogniive level providing a necessary link beween he brain and behaviour. In he ensuing secions, we highligh he links beween hese hree levels of invesigaion and explanaion wherever possible. Phonological defici: heory and evidence The phonological defici heory is he bes developed and suppored of he heories of dyslexia. Is basic premise is ha he difficulies manifesed in dyslexia (especially hose relaed o reading and spelling) are caused, wholly or in par, by difficulies in he speech sound (or phonological) sysem of language. This heory has been widely researched, in he UK, he US, and in numerous oher counries. Many US researchers have invesigaed he phonological defici hypohesis since he early 1980 s, and his has led o he invesmen of more han $15 million annually by he US governmen, via he Naional Insiue for Child Healh and Human Developmen (NICHD).
8 There is unanimous agreemen ha problems wih phonological processing are associaed wih dyslexia. Phonological processing is assessed by a variey of ess relaed o he abiliies o perceive, produce, manipulae, analyse and remember he sounds of spoken language. A widely used approach o assessing phonological processing, especially in children, is he use of phonological awareness asks. These include skills such as breaking down words ino heir sound pars, or making judgmens abou hem. For example, knowing ha ca can be divided ino is onse consonan /k/ and rime uni /a/, and ha in urn, is individual sounds (phonemes) are /k/ /æ/ //, or, judging ha ca rhymes wih ma, are all demonsraions of phonological awareness. Alhough awareness can occur a various levels, such as he syllable, he onse and rime, i is awareness of individual phonemes (speech sounds) ha is he skill mos criically relaed o emergen lieracy (Byrne, 1998; Hulme e al., 2002). Phoneme awareness helps children o learn he connecions beween alphabe leers and heir sounds and hese skills need o develop by he ime children begin o learn o read alphabeic orhographies, like Welsh and English, if hey are o learn successfully. Children who canno learn hese connecions effecively are limied in he sraegies ha hey can use o read words; for example, hey may need o rely on memorizing prined words as wholes, or on guessing, and of course his would seriously limi heir abiliy o learn o read new words auonomously (Share, 1999; Byrne, 1998; Hacher, Hulme, & Ellis, 1994). There is solid evidence daing from he seminal work of Bradley and Bryan (1983), ha phonological awareness, as well as a variey of oher phonological processing skills, including rapid pronunciaion of words, he repeiion of nonsense words, and verbal shor erm memory are impaired in children wih dyslexia and he impairmens persis ino adulhood. For recen reviews of he area see Hulme and Snowling (2009), Velluino, Flecher, Snowling, and Scanlon (2004). Some of he mos informaive sudies fall ino 3 groups: Predicing which children from a populaion a geneic risk are likely o develop dyslexia. Longiudinal sudies on oucomes for individuals wih childhood disorders relaed o lieracy. Inervenion sudies assessing eaching approaches o ameliorae lieracy difficulies (hese are reviewed in Chaper IX on inervenion). These ypes of sudies provide evidence ha he efficiency of phonological processing is crucial o lieracy developmen. In addiion, however, recen sudies recognize ha dyslexia frequenly presens as a complex disorder, and some addiional imporan predicors of progress have been invesigaed. a) Sudies of a risk populaions. These sudies have examined pre school children wih a family hisory of dyslexia for early indicaions of dyslexia (Gallagher e al., 2000; Penningon & Lefly, 2001; Scarborough, 1990). There is srong geneic evidence ha children who have a paren(s) wih dyslexia have a 50% chance of having difficulies hemselves (see Fisher e al, 2001, and he secion on III.ii below), so his is an imporan group o arge in order o find ou more abou pre school developmen and abou heir longer erm oucomes. In a series of sudies by Snowling and colleagues, a cohor of children a risk of dyslexia was followed from he age of 45 monhs unil 13 years. The researchers found ha leer recogniion of 45 monh olds proved he bes predicor of lieracy aainmen a 6 years; moreover, hose children who were already showing a lieracy delay a age 6 had also experienced delays in all aspecs of language developmen (Gallagher e al, 2001). Follow ups a age 8, and again a age 13 (Snowling, Gallagher & Frih, 2003; Snowling, Muer, & Carroll, 2007; Muer & Snowling, 2009) indicaed ha family risk was coninuous. Those who had shown lieracy delays already in early childhood wen on o have serious lieracy, phonological, and oral language difficulies in laer childhood and adolescence, and, even hose a risk children who had shown no major reading difficulies in he early school years, wen on o experience suble bu significan difficulies in he areas of spelling, phonological processing and fluency in laer developmen. In conras, a proecive facor ha moderaed he severiy of children s lieracy difficulies was expressive vocabulary and good verbal skills. Long erm predicors of poor oucomes included he presence of cooccurring difficulies (in addiion o heir phonological difficulies) in areas such as aenion, mahemaics, fine moor conrol, and spoken language, alhough none of hese on is own was associaed wih poor reading. Finally, a finding wih srong educaional implicaions was ha from 8 o 13 years of age, dyslexic children s reading abiliy remained sable; here was no evidence of caching up despie coninued schooling.
9 b) Longiudinal sudies conrasing dyslexia and oher developmenal disorders. Anoher way o invesigae he cogniive and behavioural markers of dyslexia is hrough longiudinal sudies ha follow groups of children who do or do no presen wih behavioural markers of dyslexia over periods of monhs and years in order o rack heir developmenal rajecories, and o validae ha he behavioural markers indeed specifically predic dyslexic difficulies in laer years. In ligh of findings ha dyslexia is a language based disorder, numerous sudies have sough o disinguish beween children wih early language difficulies (LI) and/or speech sound disorder (SSD), who go on o have dyslexic ype difficulies wih word recogniion and spelling, and hose who go on o have broader language and lieracy difficulies, including poor reading comprehension (see Bishop & Snowling, 2004, and Penningon & Bishop, 2009, for a recen review). These sudies reveal a complex picure of he causes and risk facors of dyslexia. In a represenaive series of sudies by Bishop and colleagues (Bishop & Edmundson, 1987; Bishop & Adams, 1990; Sohard, Snowling, Bishop, Chipchase & Kaplan, 1998; Snowling, Bishop & Sohard, 2000), children who had been idenified wih language deficis in pre school were followed up in erms of heir lieracy oucomes in primary school (age 8), and as eenagers (age 15). Alhough 65% of he children wen on o have reading difficulies, heir rajecories differed from ypical profiles of pure dyslexics. For example, he LI children s reading skills deerioraed over ime, whereas he reading skills of dyslexic children end o remain weaker bu sable over ime. Moreover, he LI children wen on o develop spelling skills ha were relaively sronger han heir reading skills, while he opposie paern is ypically found in dyslexia. Also, nonverbal inelligence was found o be he mos proecive facor agains coninuing difficulies; his suggess ha LI children wih good visual and nonverbal reasoning skills migh be able o acquire beer memory represenaions for word spellings han hose wih weak nonverbal skills. Several more recen sudies direcly conrasing children wih dyslexia and hose wih LI and/or wih SSD furher sugges ha while phonological processing deficis presen a risk facor for all hree disorders, a proecive facor miigaing poor reading oucomes is rapid auomaised naming (RAN) abiliy (see below). Togeher, hese sudies show ha while here are some overlaps beween he cogniive and behavioural markers of LI and dyslexia, he developmenal profiles of each disorder also differ from each oher in key ways. A series of cross secional sudies by Ramus and colleagues clearly showed ha phonological problems have a higher incidence han any of he oher deficis in dyslexia (Ramus, Pidgeon & Frih, 2003; Whie, Milne e al., 2006). However, he emerging research reveals ha he severiy of reading problems is frequenly compounded by oher facors ha conribue o he expression of dyslexia in hose a risk. Verbal shor erm memory defici an aspec of phonological processing. The mos consisenly observed memory deficis among dyslexics involve verbal shor erm memory and working memory. Memory deficis refer o difficuly reaining informaion necessary for performing asks. Verbal shor erm memory This involves he emporary sorage of informaion. Memory span asks, which require he spoken recall of liss of words or digis, are generally used as measures of shor erm memory capaciy. For example, he Forward Digi Span ask, is a par of mos es baeries of psycho educaional abiliy, and i is mos widely used o assess his aspec of memory (Nelson & Warringon, 1980). Working memory This involves he concurren sorage and processing or manipulaion of informaion (Archibald & Gahercole, 2006). For example, he Backward Digi Span ask is ofen used o assess working memory. The ask is similar o he forward digi span, however, i requires ha digis are recalled in he reverse order of presenaion. I is considered a es of working memory because in addiion o soring he digis for recall, he digis also have o be processed/manipulaed for presenaion in he reverse order. Summary of Research findings on Memory Deficis The exisence of memory deficis in dyslexia is well esablished by research (Cohen Mimran & Sapir 2007; Gahercole, Alloway, Willis, & Adams, 2006; Nelson & Warringon 1980; Schuchard, Maehler, & Hasselhorn, 2008). Evidence has been repored of deficis in verbal shor erm memory, working memory, and long erm memory (Gahercole e al., 2006; Jorm, 1983; Nelson & Warringon, 1980). As wih oher markers of dyslexia, some researchers have argued for he exisence of a domain general processing defici among dyslexics, affecing
10 several areas of memory, while ohers argued for a domain specific defici affecing discree areas such as verbal shor erm memory (Cohen Mimran & Sapir 2007). The areas of memory in which deficis are mos commonly found are, indeed, verbal shor erm and working memory. For example, in a review of specific reading reardaion and working memory deficis, Jorm (1983) repored reduced memory span and poor shor erm memory for serial order among poor readers. Also Nelson and Warringon (1980) found ha dyslexic children had deficis in shor erm memory and verbal long erm memory, while in a more recen sudy, Gahercole e al. (2006) found, in addiion, working memory deficis among children wih reading disabiliies. Possible causes of memory deficis idenified by research include funcional inefficiencies in brain regions such as he inferior parieal lobe and lef emporal lobe (Beneveni, Tønnessen, Ersland, & Hugdahl, 2010; Nelson & Warringon 1980). I is suggesed ha deficis in memory may affec reading acquisiion and comprehension due o impairmen in he rerieval of phonological informaion from long erm memory and inadequae sorage of informaion abou words (Jorm, 1983). The presence of memory deficis associaed wih dyslexia have implicaions for boh assessmen and inervenion. Thus, in ligh of heir prevalence, esing for hese deficis needs o be included in assessmen. Esimaing he Phonological Defici Measures of phonological processing This is he mos prevalen feaure of dyslexia. The way i is measured varies wih age wih some ess being beer suied for younger children while ohers are more suiable for aduls. While accuracy is he mos reliable measure wih children, response speed is he mos appropriae way o measure phonological abiliies in older children and aduls. Below is a brief summary of some of he aspecs of phonological processing ha have been invesigaed. Phonological Awareness includes he abiliy o consciously manipulae and make judgmens abou unis of sound in spoken words and nonwords. Task difficuly can be manipulaed o be suiable for younger and older children, and aduls. Phonological fluency requires pronouncing as many words and non words as possible in a shor amoun of ime. The challenge is o name aloud as many iems as possible ha share a phonological aribue wih a promp word (e.g., words ha share he firs/las sound as he promp). This measure is simple o adminiser, and suiable for children and aduls. Non word reading Tesing he accuracy and speed wih which non words (e.g., SMIP, HEFLIN) are read. Along wih spelling i is seen as more suiable for idenifying phonological deficis in aduls, especially hese who are well compensaed. Digi Span involves he verbal recall (repeaing) of groups of digis of increasing lengh in he same order of presenaion. The more digis recalled, he greaer he memory capaciy. Word Span uses words or non words for recall insead of digis. Implicaions for diagnosis and inervenion I is now srongly recommended ha assessmen and diagnosic es packages include asks assessing phonological processing skills. Is i relevan o Welsh? Cerainly. Phonological awareness deficis have been found o be predicive of reading and spelling oucomes in numerous languages, including Welsh.
11 Rapid auomaised naming (RAN) defici: Theory and evidence Rapid auomaised naming (RAN) asks are simple measures of he speed wih which a small number (e.g., 5 6) of repeaing simuli, such as depiced objecs, numbers, leers or colours, are verbally named. The simuli are normally presened on a grid of approximaely 8 objecs on each of 5 rows, and he ask is o name each iem quickly in serial order. The ime aken o complee he ask is he criical measure in mos versions of RAN. The RAN defici refers o a slow and efforful performance on hese simple naming asks. Summary of research findings on he RAN defici RAN has proven o be anoher very imporan marker of dyslexia and here is srong and consisen evidence of a rapid naming defici among many (hough no all) dyslexic individuals (Denckla & Rudel 1976; Semrud Clikeman, Guy, Griffin, & Hynd 2000; Wolf, Bowers, & Biddle 2000). RAN speed is a significan predicor of word reading abiliy and disabiliy in children (Lervåg & Hulme, 2009), and is prediciveness persiss ino adulhood (Wolf & Bowers, 1999). Research also indicaes ha in ransparen orhographies (e.g., German, Norwegian), he RAN defici is a sronger long erm predicor of reading difficulies (dyslexia) han are phonological abiliies (Lervåg, Bråen, & Hulme, 2009; Wimmer, Mayringer, & Landerl, 2000). RAN is mos predicive of aainmens in reading fluency (speed) and comprehension. Given he clear associaion beween RAN and reading abiliy, a grea deal of effor has gone ino undersanding he naure of his link; however, his has proven surprisingly elusive. The RAN ask, alhough very simple o adminiser, is in fac quie complex and involves numerous componen skills, such as speeded access o he name of he picure/symbol, ariculaion (in naming aloud), racking he sequence of picures/symbols, and susaining concenraion for he whole se of simuli. I is no clear which componen(s) cause(s) he rapid naming defici. Researchers are currenly debaing wheher i is simply an exension of he phonological defici, reflecing difficulies such as poor speech encoding, or slow verbal rerieval (e.g., Wagner, Torgesen & Rashoe, 1994). This explanaion is no likely o provide a complee explanaion, however, because RAN deficis are someimes found in he absence of phonological problems, and are neverheless linked o slow reading (Powell, Sainhorp, Suar, Garwood, & Quinlan, 2007; Wimmer, e al., 2000). Anoher explanaion proposes he RAN defici o reflec poorly developed connecions beween visual symbols and verbal labels, including speech sounds and leers (e.g., Lervåg & Hulme, 2009), or a fauly iming mechanism ha links phonological and orhographic forms alhough he laer mechanism remains ill defined and unidenified (Wolf & Bowers, 1999; Wimmer, e al., 2000). Ohers sill sugges he key difficuly o be suble visual aenional processing delays (Denckla & Rudel, 1976), or differences in sraegic conrol of eye movemens, based on differences in reading skill and experience (Clarke, Hulme, & Snowling, 2005). In an eyeracking sudy, Jones, Obregon, Kelly, & Branigan, (2008) idenified boh visual and phonological componens in RAN bu noed ha he greaes deficis emerged in componens of he ask ha included naming (i.e., phonological processing). Anoher view suggess ha RAN deficis reflec a domain general processing speed disorder (see also he secion on Processing Speed Defici below), which possibly includes phonological, moor and orhographic componens (Korhonen, 1995; also see discussion in Penningon & Bishop, 2009). Clearly, alhough he RAN defici sill awais a full scienific explanaion, i presens an imporan diagnosic ool for he assessmen of dyslexic difficulies and is indicaive of slow and efforful reading. Double Defici (of phonological processing and naming) In one of he more recenly developed heories, Wolf and Bowers (1999; Wolf, 2001) have brough ogeher he phonological and naming speed problems in he double defici hypohesis, which suggess ha here are wo separae sources of difficuly in dyslexia, phonological processing and naming speed. In fac, according o he proponens of he double defici hypohesis, hese wo deficis presen he main cogniive deficis underlying developmenal dyslexia. Relaive o children who experience only one of he deficis, children wih boh have he mos severe problems. As menioned in he previous secion, recen research has revealed fluen naming (i.e., good RAN performance) o be a proecive facor in he ligh of phonological processing deficis (Bishop, McDonald, Bird, & Hayiou Thomas, 2009); i remains o be seen wheher he reverse also holds rue.
12 The RAN defici Educaional implicaions I is clear o praciioners ha accuracy is no enough o make children good readers, and ha hey need o develop fluency as well. Dyslexic children wih RAN deficis need longer o read even hose words ha are familiar o hem (van der Leij & van Daal, 1999), and his may lead o ineffecive sraegies for word recogniion, such as processing large groups of leers in reading, raher han breaking he word down phonologically in order o read unfamiliar words. This approach makes heavy demands on working memory, and limis he new words ha can be ackled. Frusraingly, inervenion sudies aimed a improving naming speed and reading fluency have me wih lile success, o dae (de Jong & Vrielink, 2004; Thaler e al., 2004). Oher Observed Deficis In he ensuing secions, we presen brief descripions of several oher deficis ha have been observed and heir associaed heories. Unlike he Phonological and RAN deficis, he ones described below have a less consisen body of evidence supporing hem, alhough some of he heories are relaively new and herefore awai furher research. Much of he research summarised below may be beer undersood in erms of comorbid difficulies (a opic we cover in Chaper V). Tha is, he less sysemaic findings may reflec he fac ha he condiions described do no define or cause dyslexia, bu may co occur wih i and compound is effecs in some bu no all individuals wih dyslexic difficulies. Processing Speed Defici: Theory and Evidence Speed of informaion processing refers o he rae a which sensory informaion enering he nervous sysem can be processed (Bonifacci & Snowling, 2008). A processing speed defici refers o a deficiency in he rae and he efficiency wih which informaion is processed. Processing speed is usually assessed using reacion ime asks which measure he rae of response o differen simuli. Summary of research findings on Processing speed defici Many sudies repor dyslexics o be slower on various ypes of speeded asks, including hose where rapid sensory processing is no needed (Nicolson & Fawce, 1994b; Miller, Kail, & Leonard, 2001). Addiionally, research indicaes ha his impairmen may increase as he ask demand increases (Nicolson & Fawce 1994b). Problems may be found even when language is no involved. For example, Nicolson and Fawce (1994b) repored ha children wih dyslexia were slower o simply press a buon when choosing beween a high and a low one. In a sudy which measured he speed of brain waves o see wheher he problem lay in regisering he one (sensory) or caegorising i as high/low, (using EEG evoked poenials) Fawce e al., (1993) found slowed cenral audiory informaion processing (see recen cerebellar research below). These auhors furher proposed ha he speed impairmen may affec eiher percepual classificaion or cenral decision processes. However, he findings regarding a general processing speed defici in dyslexia are no unanimous. Some sudies have found he performance of dyslexic children (Bonifacci & Snowling, 2008) and aduls (Judge, Caravolas, & Knox, 2006; 2007) o be similar o heir peers. For example, Judge e al., (2006, 2007) found aduls wih developmenal dyslexia o have no processing speed impairmens on non linguisic asks, however hese same individuals showed serious deficis in speeded phonological awareness asks. This finding fis wih he view ha dyslexics have a defici in speed of processing in he aural, phonological sysem used for reading (Brezniz, 2001 as cied in Brezniz & Meyler, 2003). Despie he above differences in experimenal findings in groups of dyslexics, processing speed has been found o be a predicor of reading comprehension and word recogniion (Cas, Gillispie, Leonard, Kail, & Miller, 2002). As repored earlier, some recen findings sugges ha he RAN defici is bu one aspec of a domain general processing speed disorder (Korhonen, 1995; Penningon & Bishop, 2009). To summarise, here is as of ye uncerainy abou wheher he defici is domain general (affecing all cogniive processes) or specific o cerain modaliies (such as visual and audiory processes). However, from a diagnosic poin of view, speed of processing skills should be assessed as hey may be posiive markers of dyslexia.
13 Execuive Funcion Defici: Theory and Evidence Execuive funcion refers o a number of differen cogniive abiliies such as inhibiion (he prevenion of a behavioural or verbal response), organizaion, sequencing, problem solving and planning. Various asks have been used o assess he differen aspecs of execuive funcioning. Summary of findings on Execuive Funcioning Defici Research on an execuive funcioning defici among dyslexics is limied bu has provided some insighs (Brosnan e al., 2002; Helland & Asbjornsen 2000; Reier, Tucha, & Lange 2005; Wolf, Sambaaro, Lohr, Seinbrink, Marin & Vasic, 2010). Deficis have been found in aspecs of execuive funcioning including inhibiion and sequencing. However, here is some inconsisency in he aspecs of execuive funcioning in which a defici may occur. For example Brosnan e al., (2002) found ha dyslexic aduls exhibied deficis in inhibiion and sequencing, while dyslexic children only exhibied an inhibiion defici. Reier, Tucha and Lange, (2005) found a mild inhibiion defici among dyslexic children when engaged in demanding asks bu no on simpler ones. Similarly Smih Sparks, Fisk, Fawce, & Nicolson, (2003) found significan differences in he performance of dyslexic aduls and conrols on a spaial memory updaing ask (he recall in serial order of he posiions of he las four iems in a sequence) as he ask became harder. And, Helland & Asbjornsen (2000) idenified deficis in dyslexic children in several aspecs of execuive funcioning, including he abiliy o mainain focus on relevan simuli, and o change focus. Thus, numerous sudies have documened some impaired execuive funcions in dyslexic populaions, and alhough no clear paern has emerged across abiliies, weakness in he abiliy o inhibi responses seems o be frequenly observed among dyslexic children. Implici Learning Defici: Theory and Evidence Implici learning refers o he abiliy o learn paerns or regulariies wihou conscious aenion or effor o learn. Implici learning occurs uninenionally and unconsciously, and can also be described as passive learning. I is conrased wih explici learning, which is an acive process where individuals seek ou informaion. Implici learning is imporan in learning skills such as riding a bicycle, however, reading researchers argue ha i should also be implicaed in orhographic learning (e.g., Pacon, Fayol, & Perruche, 2005). For example, even very young readers are sensiive o various regulariies of heir spelling sysem (such as he fac ha English words can end in doubled consonans bu can no begin wih hem) despie never having been augh his paern explicily (Cassar & Treiman, 1997). I has been argued ha dyslexic individuals may have a defici in his ype of learning, because one of heir hallmark difficulies is specifically in learning and applying accurae spelling knowledge. Alhough some researchers see implici learning as a domain naurally suied o lieracy learning, he asks ha have been radiionally used o assess his abiliy do no involve any learning of real spelling paerns. One of he mos commonly used asks is called he Serial Reacion Time ask in which paricipans need o deec cerain visual iems from serially presened sequences of iems. Unbeknowns o he paricipan, he simuli occur eiher in a srucured, predicable sequence, or, in a random sequence. If implici learning occurs, he individual should perform more quickly on he paerned rials han on hose ha are randomised. Summary of findings of Implici Learning Defici There is a pauciy of research in his area and he resuls o dae have been inconsisen. A number of sudies have found ha dyslexics exhibied an implici learning defici (Menghini, Hagberg, Calagirone, Perosini, & Vicaria, 2006; Vicari e al., 2005 & Vicari, Maroa, Menghini, Molinari, & Perosini, 2003). The defici was found on boh sequenial and procedural learning asks in dyslexic children and on sequenial learning asks in dyslexic aduls (Menghini e al., 2006; Vicari e al., 2005 & Vicari, e al., 2003). However, oher sudies have found dyslexics no o be deficien in implici learning. Kelly, Griffihs and Frih, (2002) found no implici learning defici in dyslexic universiy sudens on mooric and cogniive sequenial asks, and, Roodenrys and Dunn (2008) found dyslexic children o be unimpaired on implici learning in a simple cued reacion ime ask. Auomaisaion/Cerebellar defici: Theory and Evidence In a number of sudies by Fawce and Nicolson, dyslexic children were found o have problems across he board, on asks including balance (Fawce & Nicolson, 1992b; Nicolson & Fawce, 1990), moor skill (Fawce & Nicolson, 1995b), phonological skill (Fawce & Nicolson, 1995a), and rapid processing (Fawce & Nicolson, 1994). This paern of difficulies was aribued o he auomaisaion defici hypohesis (Nicolson & Fawce, 1990),
14 which proposes ha dyslexic children have problems in fluency for any skill ha should become auomaic wih exensive pracice. This hypohesis implicaes he cerebellum as a brain srucure ha underlies failures in auomaisaion. Much of he recen research on auomaiciy has concenraed on balance problems in dyslexia. A mea analysis of balance deficis in 17 papers (Rochelle and Talco, 2006) idenified effec sizes of beween 0.44 0.78 in he sudies analysed, providing moderae suppor for his defici. However, he auhors found subsanial variabiliy across he sudies and concluded ha he associaion of poor balance wih dyslexia was moderaed by he presence of oher difficulies and by levels of IQ; in oher words, deficis of balance may indicae increased risk of developmenal disorder, bu are unlikely o be uniquely associaed wih dyslexia. (pp. 1159). Several researchers have argued ha balance problems may relae more paricularly o aenion defici disorder (ADHD), which is someimes comorbid wih dyslexia (Wimmer, Mayringer, and Raberger, 1999; Rochelle, Wion, & Talco, 2009). From a more applied perspecive, Berninger and her colleagues (2008) have noed he impac of lack of auomaiciy in wriing and spelling on response o inervenion in dyslexic children, alhough hey link hese difficulies o weaknesses in execuive funcions. Problems in moor skill and auomaisaion may be associaed wih dysfuncion in he cerebellum. Fawce and colleagues proposed ha a cerebellar defici could explain he range of problems suffered by children wih dyslexia, and esed his idea looking firs a behaviour and hen a he brain. Nicolson, Fawce and Dean (1995) repored ha dyslexic children showed a paern of poor performance on ime esimaion, a ask ha Ivry and Keele (1989) found only in cerebellar paiens. Children wih dyslexia also showed a range of classic cerebellar signs (Fawce and Nicolson, 1999; Fawce, Nicolson and Dean, 1996) wih problems in muscle one and balance in 80 90% of he children esed. Nicolson, Fawce and Dean (2001) also found ha dyslexics require longer o acquire even he mos basic moor skills, such as pressing buons, and ha hey may also have abnormaliies in fundamenal learning processes such as classical condiioning, habiuaion, response uning and error eliminaion in eye blink condiioning sudy (Nicolson e al., 2001; Coffin, Baroody, Schneider, & O Neill 2005). However, here is conroversy abou he exen o which he above difficulies are specific o dyslexia; hey may beer be explained by he common overlap wih DCD and ADHD (see Chaper V). Three recen reviews bes summarize he sae of he ar in his research area. Soodley and Schamaman (2009) showed ha he cerebellum was involved in moor, somaosensory, language, verbal working memory, spaial, execuive funcion and emoional processing. In her evaluaion of his area of research, Bishop (2002) proposed mehodological improvemens for advancing research, in paricular in he neuroimaging sudies of cerebellar deficis in dyslexia. These improvemens include (1) assessing more clearly wheher he dyslexic paricipans show signs of poor auomaisaion in reading (i.e. are slow readers), (2) esing for signs of concomian language impairmens, (3) esing for behavioural signs of poor moor funcion, as a proxy for cerebellar dysfuncion, (4) invesigaing wheher he paricipan has a family hisory of dyslexia, and where possible (5) esing for impairmens of magnocellular funcioning (see below), as hese have been proposed o be clearly associaed wih cerebellar dysfuncion. A recen review, Soodley and Sein (2009) has concluded ha, alhough i is likely ha he cerebellum is par of he disurbed neural circuiry ha is impaired in developmenal dyslexia (pp. 1), here is considerable inconsisency in he research findings and many sudies find no evidence of general impairmens in auomaiciy, or of cerebellar impairmens; hese auhors conclude ha i remains unlikely ha cerebellar dysfuncion is he main cause of dyslexia (pp. 1). In sum, as in many areas of research ino dyslexia, he cerebellar impairmens hypohesis awais furher invesigaion and refinemen. A presen, he evidence suggess ha some people wih dyslexia have impaired cerebellar funcioning, however he causal connecion beween hese wo disorders remains unclear. Sensory Magnocellular Deficis Anoher area of research has focused on dyslexic children s difficulies in processing informaion coming in via he senses (sensory informaion); ha is, informaion coming from boh he ears (audiory) and he eyes (visual). This ype of processing is conrolled by he large cells in he magnocellular pahways, which go o a par of he brain
15 known as he halamus. Differences have been found in he dyslexic brain anaomy in boh visual and audiory magnocellular pahways (Galaburda, Menard and Rosen, 1994; Livingsone, Rosen, Drislane & Galaburda, 1991). Audiory percepual deficis According o his heory (Tallal, 1980), he phonological defici is he consequence of a more basic defici in he audiory processing sream. Proponens of his heory claimed ha, like language disordered children, hose wih dyslexia ake longer o process sounds which change rapidly (Tallal, Miller, & Fich, 1993). This is esed wih he Audiory Repeiion Task (ART) in which high and low ones, or he sounds ba and da are presened (which only differ from each oher in he firs few milliseconds), and he lisener has o reproduce he order in which he sounds occurred. Children wih dyslexia and wih SLI were unable o ell he difference beween he sounds if hey were presened in quick succession, and his difficuly was associaed wih poor phonological awareness. This poenially imporan heory araced a number of aemps a replicaion, and as a consequence he audiory defici is now beer undersood. I is now clear ha he ART defici is found in some children wih language impairmens, of whom some may also have reading difficulies. For example, he carefully designed sudy of Heah, Hogben, and Clark (1999) revealed ha dyslexic children who had no concomian oral language problems were as good as ypical readers on he ART ask; in conras, 55% of he children wih oral language difficulies and dyslexia experienced significan difficulies on he ART while he remaining 45% (wih less severe language impairmens) were comparable o ypically developing children. Moreover, ART performance and phonological skills were weakly associaed. Thus, audiory processing deficis are found among some children wih dyslexia who also have language impairmen; bu, imporanly, his difficuly seems no o be a direc cause of heir lieracy difficulies. Visual processing defici A problem in he processing of low level visual informaion in people wih dyslexia was firs idenified by Lovegrove (1993; Lovegrove, Marin and Slaghuis, 1986), who found ha if a flickering paern was shown o dyslexic children (hink of he lines on a elevision screen), hey needed a more defined flicker before hey were aware of i. Along similar lines, Talco e al. (1998) showed ha dyslexic children needed more informaion o deec a paern of simuli moving ogeher, like clouds, agains a randomly moving background (a ask known as coheren moion sensiiviy). However, more recen research in his area has failed o find a magnocellular defici among dyslexics. For example, in a sudy wih children, Hulslander e al. (2004) found no difference beween good and poor readers (including some wih dyslexia) on a measure of moion coherence sensiiviy (cf., Talco e al., 2000). Moreover, reading abiliy and moion sensiiviy hresholds did no correlae when IQ was aken ino accoun; however, he wo groups differed significanly on phonological awareness. Using a differen measure of magnocellular funcion (deecing a low spaial frequency flickering simulus), Williams, Suar, Casles and McAnally (2003) found no differences beween groups of dyslexic and conrol children. And, in a recen large scale sudy wih aduls, Heah, Bishop, Hogben and Roach (2006) found ha wo common measures of magnocellular processing (coheren moion and flicker sensiiviy) correlaed poorly wih each oher, raising he possibiliy ha hey do no reliably ap magnocellular funcion or ha hey are no funcionally relaed o each oher. In addiion, hese auhors found a small subgroup of dyslexic aduls o perform less well han a conrol group on he wo visual asks, however, neiher of hese asks correlaed wih reading abiliy. A similar finding was observed by Ramus e al. (2003), and by Judge e al. (2006). Thus, ye again, i seems ha sensory deficis in vision and audiion may occur in some individuals wih dyslexia, however heir connecion o dyslexic lieracy difficulies is enuous, and probably no causal. Despie he inconsisencies in he research findings, his coninues o be an acive area of research (e.g., Laycock & Crewher 2008; Poldrack e al., 2001), which promises o advance our undersanding of percepual deficis of vision and hearing, if no necessarily in dyslexia. Visual Aenion Defici In conras wih visual percepion processes, visual aenion (no o be confused wih Aenion Defici Hyperaciviy Disorder) refers o how aenion is disribued when focusing on paricular simuli (Valdois, Bosse, & Tainurier, 2004). However, visual aenion does no refer o a uniary consruc. For example, asks o assess visual aenion include measures of he abiliy o direc and focus aenion, o deec visual objecs in a scene,