Studies on spelling in the context of dyslexia: a literature review

Mailing address: Luciana Cidrim Calado Meira Rua Carlos Pereira Falcão 298 – Boa Viagem CEP: 51021-350 Recife, Pernambuco, Brasil E-mail: lucianacidrim@terra.com.br ABSTRACT This paper aimed at reviewing the literature related to national and international research on spelling difficulties by dyslexics and identifying the intervention approaches performed with regard to this topic. An integrative review of the literature was carried out in order to answer the question: considering the domain of the orthography, one of the challenges frequently faced by dyslexics, how are studies on the relationship between dyslexia and spelling characterized? The research was carried out in PubMed platform, Scopus database and Portal de Periódicos CAPES/MEC. To search the articles, the following descriptors were used: “dislexia” or “dyslexia” with the free terms “ortografia” or “spelling”. One aspect should be highlighted: some works indicate that difficulties in the spelling performance by dyslexics are not exclusively due to phonological processing failures – they are also secondary to alterations in orthographic processing. A challenge faced by dyslexics is to retain phonological information to use in writing new orthographic forms. Researchers suggest that intervention strategies include phonological, orthographic and lexical activities. It is observed that few studies have analyzed the difficulties that dyslexics face when dealing with new words, as well as writing, correctly, frequently used words in their own language.


INTRODUCTION
There is currently a constant concern from both medical and educational scope regarding difficulties on learning how to read and how to write.
Learning how to write is underpinned by a series of properties and aspects of the written form that are part of the orthographic system [1][2][3] .This type of learning incorporates how to differentiate the formation of letters, to develop phonological awareness, to establish quantitative correspondence, to identify the position of letters in a word, to understand that the same letter may represent different sounds, as well as to understand that the same sound can be represented by different letters.Therefore, writing orthographically is not an easy task 3 .
The orthographic knowledge refers to the understanding of how letters are combined to form words, being acquired through repeated exposure, acquisition of phonological awareness and knowledge of the rules for the formation of the orthographic mental lexicon 3,4 .
Spelling errors are part of the infant's learning process 1,3,5 .Although kids progressively overcome those errors as they obtain deeper understanding of the features of the orthographic system they use to write, the persistence of errors and the kind of errors they make might indicate some learning disability 3 .Dyslexia as a functional learning disability is a neurological disorder characterized by specific difficulties in the reading and writing skills, which are not secondary of cognitive alterations, neither lack of opportunity in formal education 6 .
Researchers point out that, regarding dyslexia, the major focus of most studies has been reading difficulties, and there is less research about the orthographic processing in dyslexic children 2,3,5,[7][8][9] , although to correctly underline words be a challenge that might extend to adulthood 10 .Regarding learning problems, the investigation focus should not be limited to reading characteristics, it is necessary to understand the analysis of writing 3,11 .
The main goal of this study is to revise scientific literature that is related to research about spelling difficulties faced by dyslexic, as well as to identify approaches of interventions on the aforementioned theme.

METHODS
An integrative review of the literature based on national and international research was carried out to answer the following question: Considering the orthographic system skills one of the challenges most commonly faced by dyslexics, how are the studies about the relation between dyslexia and spelling characterized?
The research was carried out in PubMed platform, Scopus database and Portal de Periódicos CAPES/ MEC.To search the articles, Descriptors in Health Science (DeCS) and Medical Subject Headings (MESH) were used in combination: "dyslexia" or "dislexia" and the free terms "spelling" or "ortografia".Articles that were published within the last five years were selected through advanced search, excluding books.To search the combined terms, the option title/abstract was selected in the PubMed; title, abstract and keywords in the Scopus database and subject in the Portal de Periódicos CAPES/MEC.
The development of this article of literary review is part of a doctorate thesis, still under development, with the title "Dyslexic Sight Words (DSW) and Speech Therapy Intervention in Dyslexic children", from the Graduate program of Sciences of Language at Universidade Católica de Pernambuco -UNICAP/PE.
In this research, complete original articles or review articles published in the last five years in Portuguese or English were included, which answered the guiding question and which addressed the theme established by the descriptors and free terms.
Articles that repeated were excluded.The following exclusions were also carried out: review articles about the symptoms of dyslexia; research about orthography with non-dyslexic; neuroimaging study with dyslexics; articles about reading and dyslexia, specifically; research with dyslexics about spelling regarding the sounding out of words, instead of writing down words; articles about the executive and neuropsychological functions of dyslexia; generic studies about dyslexia, and articles about "acquired dyslexia" due to vascular cerebral accident.

LITERATURE REVIEW
The analysis of the data was divided into stages.Firstly, all articles obtained through the combination of descriptors and terms "dislexia" AND "ortografia" AND "dyslexia" and "spelling" were identified, and all abstracts were read.Afterwards, the first part of exclusion, which followed the benchmarks of this research, was realized.
All remaining articles were separated to be read in full and the repeated articles were removed.After thorough reading, other articles were eliminated because they did not meet the criterion stablished initially (Figure 1).
The selected articles were organized from the earliest to the latest according to the date of publication and, after reading each one, the following information was declared: author(s) and year of publication, constitution of sample, and description of study (Figure 2).Operational memory activities associated to reading and writing were tested in children with specific learning disorder from 4th. ao 9th.school year.It was concluded in the results that there are common difficulties among groups, especially regarding language, and stimulating operational memory helps learning to read and to write.
The main goal was to analyze the effect of the morphological knowledge about orthography in schoolchildren of the Hebrew language.Orthographic tasks as well as phonological awareness tasks were performed.In the results, it is suggested that morphological instructions help dyslexics in language learning.
Specific difficulties were described in the learning of English as a second language by dyslexic Polish students.The results confirmed that dyslexic were less fluent in reading and presentend more spelling errors of phonological type.years and 1 months.
An orthographic evaluation was carried out with three groups of children.Spelling errors were classified in phonological, morphological, and visual-orthographic.
It was concluded that the spelling performance on dyslexic children is the most severe in all types of errors when compared to the performance of the other groups.
The objective was to understand the nature of spelling errors made in Bosnian language by dyslexic children.
It was confirmed that most of the spelling errors are of phonological nature.
Palladino P et al. (2016) 17 Italy 13 dyslexic children compared to 2 groups of children: 13 children of same gender, age and IQ, and 10 children with difficulties in learning English as a second language.
Spelling skills were investigated in the learning of English as a second language by dyslexic children.Dyslexic presented severe difficulty in spelling English words and the most frequent errors were those related to the phonological representation of words.

Author(s) Country Sample Study description
Ruberto N, Daigle D, Ammar A (2016) 20 Canada 32 dyslexic children were compared with two groups of children: 24 children with same reading level and 25 children of the same age.
The orthographic strategies used by dyslexic children in dictation and spelling (sounding out letters) were analyzed.The phonological strategies are the most used by all groups.The orthographic/visual method explain the best results of the control group.Sumner E, Connelly V, Barnett AL (2016) 19 United Kingdom 31 dyslexic children were compared with two groups of children: 31 children of the same age and 31 children of the same spelling (sounding out letters) level.
It was investigated if the spelling (sounding out letters) inability, common in dyslexic, impairs written production.The results point out that spelling (sounding out letters) inability interferes on written performance.
The goal was to analyze the occurrence of spelling errors made by dyslexic adults and non-dyslexic adults when searching on Google.Dyslexics presented a higher number of spelling errors, they also looked at the screen fewer times during the research.If the autocomplete suggestions were used at a higher frequency, the number of spelling errors would be fewer.
Texts were produced using a computer keyboard: a regular keyboard and a keyboard with its letters covered.
Dyslexic made more spelling errors and wrote shorter texts using the keyboard with the covered letters.
Reading and spelling gains by dyslexic and non-dyslexic were investigated through phonic intervention.Dyslexic presented lower reading and spelling levels in the pretest.After intervention, there was some progress on reading tasks and rapid automatic naming.
School progress of students from 1st to 3rd year of elementary was tracked.Throughout the study period, students were tested in phonological awareness, reading and orthography.Possible students with dyslexia profile were detected in their 1st year because of their reading and spelling performance.It was concluded that early intervention is useful to reduce schooling difficulties.The objective was to investigate the spelling deficits at adulthood.In the results, dyslexic presented more spelling errors than their non-dyslexic peers.Difficulties persisted at adulthood and they seem to be associated to a deficit that affects lexical processing.The objective was to evaluate the use of iPad in writing and orthographic training activities with children with specific learning disorders.In the results presented, children improved significantly with the assistance of technology with regards to writing speed and spelling errors recognition.
It was investigated the relation between the phonological decoding and spelling performance.In the results, it is suggested that the phonological decoding skill is not the only one requirement to acquire orthographic knowledge of words.
The types of spelling errors made by Greek and American dyslexics were characterized.In the results presented, the Greek dyslexics made less phonological errors and more grammatical errors than American dyslexics and this is due to their own linguistic properties.

Author(s) Country Sample Study description
Tops W et al.
The goal was to analyze if undergraduate dyslexic students are aware of their own spelling errors.It was concluded that there is no evidence that dyslexics make more spelling errors because they are not aware of their difficulties but because of their own linguistic impairment.
Tops W et al.
The objective was to compare the types of spelling errors of dyslexic students and non-dyslexic.Dyslexics made twice as more spelling errors than non-dyslexics.The most frequent spelling errors were of phonological nature.Hiscox L, Leonaviciute E, Trevor H (2014) 14 United Kingdom 22 dyslexic undergraduate students and 27 non-dyslexic undergraduate students.
It was investigated the relation between working memory and spelling through automatic orthographic corrector.It was concluded that the use of the software can be beneficial to dyslexics.
The objective was to evaluate the writing of dyslexic and non-dyslexic children.In the results, it was pointed out that dyslexic children spent more time to perform activities and made a greater number of errors.
The goal was to investigate the orthographic and phonological processing skills of dyslexic children.
It was reported that dyslexic presented efficient orthographic processing skills but they are hindered due to phonological inability.
Most common spelling errors made by Greek dyslexic and non-dyslexic children were classified.It was concluded that spelling errors which come from their own language arbitrary relations persist on dyslexic and non-dyslexic children.However, this difficulty is greater for children with dyslexia.
Hsu JL Spelling performance in dyslexic children was described.In the results, it is suggested that dyslexic children need more mastery in the ability to correctly spell (sound out letters) words in order to increase their access to orthography.McCarthy JH, Tiffany H, Catts H (2012) 16 United States 43 children with language disorder were compared to 21 dyslexic children and with 18 with language disorder and dyslexia.
The objective was to verify the relationship between reading fluency and spelling performance.Dyslexic children, regardless of having oral language disorder, presented low spelling performance.During the search for articles stage, even with the limitation of the free terms and/or descriptors, many works that focused on reading and dyslexia were found.In order to illustrate, an additional research of the terms dyslexia AND reading, dislexia AND leitura, dyslexia AND spelling, and dislexia AND ortografia, The data search resulted in a total of 454 articles.At PubMed, as result of the combination of terms, 136 articles were found, at Scopus database, 251 articles were found, and at Portal de Periódicos da Capes, 67 articles were found.
When taking into consideration the inclusion and exclusion benchmarks, 36 articles were analyzed in this literature review.
The distribution of the number of publications that were included in this work about "dyslexia" AND "spelling" and "dislexia AND ortografia," from 2012 to 2017 (in this last year, the period between January and April was considered) is presented in Figure 3. in the last ten years, was performed using the same benchmarks disclosed in the beginning of this session.In Figure 4, it is possible to verify superiority regarding the number of publications about dyslexia and reading when compared to the number of publications about dyslexia and spelling.
The data related to the analysis of the study selected for this review are presented in Figure 2.
Among selected articles, two publications were computed in the year 2017, sixteen in the year 2016, seven in the year 2015, four in the year 2014, five in the year 2013 and two in the year 2012.A small number of publications is observed in 2017, which is justified by the fact that the search for articles was carried out during the months of March and April 2017.The articles published in 2016 correspond to 44.44% of the selected studies.There is a growing trend in the number of publications about dyslexia and spelling, as it can be observed, for example, between the years of 2014 and 2016 in Figure 3.
In dyslexia, spelling impairments are often more extensive and persistent than in reading.This may occur due to difficulties related to the process of phonographic-orthographic conversion and its use to the correct writing of the words [1][2][3][4][5][6][7][8] .The analysis of the spelling errors made by children, in the educational and medical amplitude, might offer parameters for the identification of what is expected or not, assisting in the elaboration of plans and interventions according to the specificities of the difficulties 12 .
A study carried out with Bosnian dyslexic children 12 validated the hypothesis of phonological deficit 6 to explain the high frequency of errors in the writing of children with dyslexia, unlike results obtained in a Greek-language research 13 , with transparent orthography (greater phoneme-grapheme regularity).Studies suggest that different language structures produce different types of errors and that in languages that have a more transparent orthography there is a smaller incidence of errors 9 .In Greek there is less than half the syllables when compared to English (opaque orthographic system -irregular phoneme-grapheme relation) 13 .
The correspondence of a phoneme to a single grapheme and vice-versa is understood as orthographic transparency.However, orthographic opacity is characterized by the irregularity to which one grapheme might correspond to several phonemes, and to which one phoneme might correspond to many graphemes.This more opacity charactheristic of the language might generate some difficulties in the learning of the written language 2 .
Research with Brazilian children 1 analyzed the spelling performance of dyslexic children and children with dyslexia and ADHD (Attention Deficit Hyperactivity Disorder) by administering dictation of words.The authors suggest that dictation using balanced words can be useful to the formation of a lexicon database that can be used in future research.
In some researches 1,14 the relationship between working memory or operational memory and spelling performance in children with dyslexia was studied.The writing process is complex and encompasses distinct functions that are integrated due to operational memory skills.Dyslexics present a working memory deficit that directly affects their writing tasks performance 14 .
The occurrence of historic of oral language disorder is common in dyslexic children 6 .The spelling performance was investigated in a study with Italian dyslexic children 15 with and without history of delay in the acquisition of the oral language.The results presented themselves coherent with the hypothesis that dyslexic children with history of oral language disorder present more severe orthographic deficit.The relation between reading fluency and spelling performance was the focus of the investigation of an American study 16 which evaluated children with language disorder, dyslexic children and children with language disorder and dyslexia.It was concluded that the history of language disorder is not the cause of low spelling performance, and children that presented the gravest orthographic disorder had a reading deficit.Some studies investigated the acquisition of English as a second language (L2), in dyslexics 17,18 .The spelling performance and the most frequent types of erros were evaluated.Both studies demonstrated that the most frequent errors of dyslexics were of phonological nature.
Dyslexia is a learning disorder that affects word recognition during reading, spelling (sounding out letters) and writing.It is the result of a phonological processing deficit 19 .Phonological deficit hinders the learning of the alphabetical principle of the language, more specifically, the phoneme-grapheme correspondence 20 .In languages such as French, this correspondence is the basic aspect for the successful learning of the reading and writing skills.Dyslexic children are slower at spelling (sounding out letters) when compared to children with no specific learning disabilities 19,21 .In a study that was performed with French non-dyslexic and dyslexic children 19 , spelling skills were analyzed through dictation of words.The phonological strategy was common to the groups, even though it was not guaranteed that children would be able to spell all words correctly.The visual-orthographic strategy (visual memorization of words) was observed only in non-dyslexic children.Researchers pointed out the importance of using the visual-orthographic strategy in intervention programs to promote the acquisition of new words by children.
Researchers have highlighted that, beyond phonological decoding difficulties, learning to read new words is a challenge to dyslexic children, especially sight words, which are common words in English language that children deal with in written materials throughout their whole schooling process 22 .
To some experts 1,2,9,15,17 errors made by dyslexic schoolchildren are likely to be classified in groups.As a result of a Brazilian research 1 , it was presented that dyslexic schoolchildren and dyslexics with ADHD underperformed in writing when compared to children with no learning disorders.They made arbitrary spelling errors that are directly related to visual memory, knowledge of orthographic rules, lexicon and morphology.
The kind of phoneme-grapheme correspondence error depends on the phonetic/position context is a high frequency error category in dyslexic Brazilian children and dyslexic Brazilian children with ADHD 1 .These errors are observed in the writing of irregular words of the Portuguese language, for example: feliz by felis, dança by dansa, visual by vizual, xícara by chicara, garrafa by garafa, longe by lonje, trouxe by trousse, colégio by coléjio, faixa by faicha, macarrão by macarão, lixo by licho, among others.
Researchers have investigated the spelling performance of Spanish dyslexic children 11 and pointed out that the most relevant difficulties in dyslexics are related to orthographic rules, writing of irregular words, and phoneme-grapheme conversion skill (vaso (cup) for baso, hueco (hollow) for ueco, chaqueta (jacket) for chaceta).
Errors of phonological nature were also the most frequently observed in a research with dyslexic Bosnian children 12 .Phonological errors are result of the substitution of letters with similar pronunciation (biti by piti, slab by slap, zima by sima).
In a study performed with dyslexic and non-dyslexic French children 8 , the results demonstrated that all groups of children made the non-phonological error, for example: vert (green) by verre (cup).However, in another French study 15 , the spelling errors in dyslexic children were classified according to their nature, being the phonological ones the most frequent, for example: quota by cuota and febbre by febre.
The kind of lack or inadequate presence of accent was frequent in dyslexic Brazilian children as well 1 , which is expected, as it is related to orthographic rules that are considered complex, such as notion of syllabic division and stress of words.
In a research with dyslexic and non-dyslexic undergraduate students, it was pointed out that the occurrence of a greater number of spelling errors made by dyslexics is not due to the fact they are less aware of their difficulties, but due to their own linguistic disability 27 .
Research about learning disorder, in special dyslexia, have focused on the difficulties in acquisition of the correspondence between phonemegrapheme 12,18,22,[28][29][30] .The phonic intervention is a way to stimulate phonological skills in advance in dyslexic children 29 and on children that present early learning profile with dyslexic characteristics or other learning disabilities 4 .
A study 31 compared the spelling performance among children with dyslexia and children with ADHD.Its outcome suggested that intervention programs be distinct due to the specificity of each group.Dyslexic children made less errors when copying as compared to children with ADHD.
Researchers 1 emphasize that interventions regarding orthography must guarantee a systematic approach in the learning of the relation phonemegrapheme, and afterwards in the learning of orthographic rules both for school children without learning disabilities and schoolchildren with learning disabilities.Researchers point to a failure in formal teaching of the aforementioned aspects.
A study performed with Dutch children 29 proposed a phonic intervention program based on spelling (sounding out letters) activities associated to cards that depict images related to their phonemes.In the results presented by the study, it was observed that the intervention program improved the performance of dyslexic children regarding reading, spelling (sounding out letters) and recognizing the relation between grapheme-phoneme.Operational memory activities associated to reading and writing were suggested to be introduced in the intervention program in the spelling difficulties of dyslexic children 7 .Dyslexic Hebrews were subjected to an orthographic intervention program through activities that involved morphological analysis of words 5 .
The use of information and communication technology (ICT), such as softwares that provide orthographic auto correction, tools for evaluation of reading and comprehension of texts, and e-readers, have assisted intervention of dyslexic children 14,25,[32][33][34][35][36] .
Research has tested non-dyslexic and dyslexic children while they performed orthographic tasks [37][38][39][40] .It was suggested that evaluation activities on dyslexic children be as diversified as possible as children usually refuse to perform formal reading and writing tasks, which is justifiable due to their own learning disabilities 40 .

CONCLUSION
This study addressed national and international publications about spelling in the context of dyslexia.It was observed that some studies in the literature highlight that the difficulties in the performance of the written language in dyslexic children are not exclusively due to phonological process fail, they are also secondary to alterations in the orthographic processing.Researchers suggest that beyond phonological activities, intervention strategies should address orthographic and lexical activities.Few studies analyzed the difficulties dyslexic children present to deal with new words in written material as well as to write correctly high frequency words in their mother language.

Figure 1 .
Figure 1.Flowchart showing the number of articles found and selected after applying inclusion and exclusion criterion Rothe J et al.(2015)10 Germany 19 dyslexic children and 32 children with typical development.It was evaluated the orthographic process on dyslexic children.When compared to non-dyslexic children, they presented more difficulties at the lexical level with few skills to recognize orthographically incorrect words.Roy P et al.(2015)30 United Kingdom 68 children with intense auditory deficiency and 20 dyslexic children.The objective of the research was to verify the performance of deaf children and dyslexic children during dictation and reading.Most of spelling errors were of phonological base to both groups, suggesting the investment in phonological strategies since alphabetization.attention deficit hyperactivity disorder (ADHD) and 13 dyslexic children.The performance of children with ADHD and dyslexic children was analyzed through copy and dictation of words.The performance of the two groups was distinct: dyslexic children made less spelling errors when copying and ADHD children presented more spelling errors during copy activity.It was suggested that difficulties in dyslexic were higher on phonological matters and difficulties on ADHD children are due to their short attention span.Berninger VW et al. (2015) 34 United States 35 dyslexic and disgraphic children.
aged (11 years and 8 months) were compared with two groups: one of them composed by 31 children with average development and aged 11 years and 9 months, and the other group made of 31 children with average development with same average reading level and average age of 9 years and 8 months.It was investigated the influence of simple syllabic structures: consonant-vowel (CV), two consonant clusters (CCV) in the spelling performance of dyslexic children.It was concluded that the spelling of words that presented two consonant clusters (CCV) is more difficult to dyslexic children when compared to children with no schooling difficulties.

Figure 2 .
Figure 2. Description of selected studies.

Figure 3 .
Figure 3. Distribution of the number of publications considered in this study on dyslexia and spelling and dislexia and ortografia in the period from 2012 to 2017, by year of publication
The goal was to analyze different causes of spelling errors through dictation of words.In the results, different causes are suggested to the spelling difficulties: dyslexic children have difficulties to generalize morphologic relations and children with otitis had a phonological/ perceptive base difficulties.