Types of Developmental Dyslexia in Arabic

Abstract

Developmental dyslexia is a general term for various kinds of impair-ments in reading. More than 10 types of developmental dyslexia have been identi-fied, each resulting from a deficit to a different stage in the reading process. The different deficits give rise to different patterns of errors in the various dyslexias and to different types of words that cause difficulty in reading. In this article we present types of developmental dyslexia that we have identified in Arabic, and survey their main characteristics, focusing on the unique properties of the Arabic orthography and their interaction with the manifestation of the various developmental dyslexia types. We present the patterns of developmental peripheral dyslexias, dyslexias that result from impairment at the orthographic-visual analysis stage, and of central dys-lexias, which result from impairments at later stages. Within the peripheral dyslex-ias, we focus on the manifestation in Arabic of letter position dyslexia, which is caused by a deficit in letter position encoding and which results in letter position errors; on attentional dyslexia, a deficit in the attentional window in reading, which results in migrations of letters between words; on visual dyslexia, a deficit in the orthographic-visual analyzer that causes letter omissions, additions, substitutions, and migrations; and on left neglect dyslexia, a disorder that leads to visual errors only on the left side of words. We then report and discuss the manifestation of cen-tral dyslexias in Arabic: surface dyslexia—a deficit in the lexical route that causes reading via the sublexical route; vowel dyslexia—a selective impairment in vowel processing in the sublexical route that causes impaired reading of vowel letters; and deep dyslexia—a deficit in the sublexical and lexical routes, which causes reading via the comprehension of the word and leads to semantic and morphological errors. All but one of the dyslexias described here are reported for the first time in Arabic. 6.1 Introduction Developmental dyslexia has many forms. Depending on the exact nature of impair-ment in the single word reading process, completely different patterns of impaired reading can arise. Indeed, there are currently more than ten known types of dyslex-ia, resulting from deficits in different loci in the reading process, each with different characteristics, and, subsequently, each requiring different treatment approaches. Importantly, the different loci of impairment in the reading process are not the only source of principled heterogeneity between individuals with developmental dyslexia. The properties of the orthography in which the dyslexic person reads cre-ate another source for differences between individuals with dyslexia. For example, individuals with a dyslexia that causes reading only via grapheme-to-phoneme con-version may find it much harder to read in an orthography like Arabic, in which many words can be read in various ways via the sublexical route due to the under-representation of short vowels in the orthography, than in other languages, such as Italian, in which grapheme-to-phoneme conversion usually yields the correct word. In the current study we survey the way the special characteristics of the Arabic or-thography affect the manifestation of developmental dyslexia in Arabic. To describe the various types of dyslexia, we will first describe the reading mod-el that we assume in this research, and then describe the various dyslexias that can result from selective deficits in various components within this model. In Fig. 6.1 we present the dual route model for single word reading. This model is the result of a work of cognitive neuropsychologists over the past 40 years, including Max Young, and others. Whereas many models of read-ing exist, this model allows the best and most straightforward way, in our minds, to account for and predict the various types of dyslexia. orthographic input lexicon