Developmental surface dyslexias

Abstract

Individuals with surface dyslexia read via grapheme-to-phoneme conversion due to a deficit in the lexical route. A deficit in the lexical route can be caused by impairments at several different loci. In the current study we identify three subtypes of developmental surface dyslexia, each caused by impairment at a different locus on the lexical route, and each showing a different pattern of performance in various tasks. All three subtypes show the classical pattern of reading aloud, with regularizations and difficulty in reading words that have more than a single possible conversion to a phoneme string, but they differ in their performance in lexical decision and homophone comprehension. The first subtype, input surface dyslexia, results from a deficit to the orthographic input lexicon, and entails poor performance in lexical decision and comprehension tasks. The second subtype, orthographic lexicon output surface dyslexia, in which the orthographic input lexicon is accessible but its output to the phonological output lexicon and to the semantic system is impaired, allows normal lexical decision, but causes impaired comprehension of homophones. The third subtype, interlexical surface dyslexia, caused by a selective deficit in the connection between the orthographic input lexicon and the phonological output lexicon but with intact access from the orthographic input lexicon to the semantic system, allows normal performance in lexical decision and comprehension tasks. Seventeen Hebrew-speaking individuals with developmental surface dyslexia aged 10-43 participated in the study, eight of them showed the first pattern, three showed the second pattern, and six displayed the third pattern. Another result of the study pertains to the importance of the lexicality of the result of grapheme-to-phoneme conversion for each target word. Some words, when read via grapheme-to-phoneme conversion, can potentially be read as other words (such as "now" in English, which can be sounded as the word "know"), we term these words potentiophones. The results indicate that potentiophones yield the highest error rate in reading aloud for all the participants with surface dyslexia.