ACQ Vol 13 no 2 2011

Assessment

Subtypes of developmental reading disorders Recent developments and directions for treatment Kristy Jones, Anne Castles, and Saskia Kohnen

This paper presents an overview of several subtypes of developmental reading disorders including phonological dyslexia, surface dyslexia, hyperlexia, poor comprehenders, and the less-recognised subtypes of letter- position dyslexia and attentional dyslexia. Although clinicians may be familiar with the symptoms of phonological and surface dyslexia, the symptoms of the other reading disorders noted may be less familiar and therefore methods of assessment and directions for treatment may be unclear. Each subtype is described and accounted for in the context of the dual route theory of reading. Current research on remediation strategies is also surveyed, providing a basis for developing treatment programs for both pure and complex developmental reading disorders. A lthough most clinicians are familiar with terms such as “specific reading disorder” or “dyslexia”, the different kinds, or subtypes , of developmental reading disorders that can affect children may not be as widely known. This is particularly true for some of the subtypes that have only recently become the focus of research attention. In this article, we outline the symptoms that characterise six specific subtypes of reading disorders and provide suggestions for diagnosis and treatment, based on theoretically driven research. It is unusual for a child to suffer from just one subtype of reading disorder. Although pure cases do exist (e.g., Broom & Doctor 1995a; Castles & Coltheart, 1996; Friedmann, Kerbel, & Shvimer, in press; Friedmann & Rahamim, 2007; Rowse & Wilshire, 2007), in most cases children with a developmental reading disorder will show symptoms associated with more than one subtype (e.g., Brunsdon, Hannan, Coltheart, & Nickels, 2002a). It should also be acknowledged that although some of the subtypes we discuss, e.g., phonological and surface dyslexia, are well- known and have been thoroughly researched in terms of causal links and treatment, other subtypes, e.g., letter- position dyslexia and attentional dyslexia, are still relatively new, with research being in its infancy. Appropriate caution should therefore be exercised in relation to decisions about assessment and treatment in the latter instances. Finally,

it should be emphasised that we see these subtypes, not as distinct subgroups that are qualitatively different from normal readers, but as subgroups at the extreme ends of a continuum of performance on a particular subskill. Before we describe the different subtypes of reading disorders, we will outline the set of processing abilities children need to acquire, to become proficient readers. In order to conceptualise the complex cognitive processes involved in reading, we rely on dual route theory (e.g., Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001; Friedmann et al., in press; Jackson & Coltheart, 2001; see Figure 1). Although there are other models of the reading process (e.g., Plaut, McClelland, Seidenberg, & Patterson, 1996), the modular nature of the dual route model makes it particularly suitable for identifying and accounting for different types of reading disorders: it is possible to easily and clearly identify the different processes that need to be acquired for skilled reading and to develop specific tests to assess the functioning of those processes. Such assessment aids clinicians in developing a focused treatment approach. According to the dual route theory, various processing steps take place from first seeing a written word to subsequently reading it aloud and/or comprehending its meaning. As illustrated in Figure 1, the initial set of processes is summarised as visual orthographic analysis . There are three functions within visual orthographic analysis. First, letter identification takes place. This involves recognising what is seen as a series of letters, not numbers or symbols. Second, letter position within a word is encoded (so that words like sliver and silver can be distinguished from each other). Last, when more than a single word is being read, letter-word binding occurs, such that the letters of each word are correctly associated with the word they appear in, and not another one (Friedmann et al., in press). For example, in order to read the two words tall walk correctly, the letters T A L L need to be associated with the first word and the letters W A L K with the second word. If the association process goes wrong, a reading error such as wall talk may occur. The word is then further processed via two different routes. The type of word that is read predicts which route will be successful in producing the correct response. Regular words (e.g., cat, hut, pet ) and words (or nonwords) that a child has never come across before can be sounded out phonetically via the letter-sound-correspondences, along the so-called nonlexical route (Coltheart et al., 2001). However, for irregular words (e.g., friend, yacht ),

Keywords DUAL ROUTE MODEL

DYSLEXIA READING

DISORDERS TREATMENT

This article has been peer- reviewed

Kristy Jones (top), Anne Castles (centre), and Saskia Kohnen

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ACQ Volume 13, Number 2 2011

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