[PS-2.15] Morphological segmentation and orthographic transparency in typical and dyslexic Hebrew readers: Evidence from brain and behavior

Weiss, Y. 1 , Katzir, T. 1 & Bitan, T. 2

1 Dept. of Learning Disabilities, The E.J. Safra Brain Research center for the study of Learning Disabilities, University of Haifa, Israel.
2 Dept. of Communication Sciences & Disorders, University of Haifa, Israel

Background: Current evidence suggests that phonological and morphological processing play a role in typical and atypical development of reading. The dual version of Hebrew script (pointed and un-pointed) and the rich morphology of Hebrew provide an opportunity to learn about the interaction of orthographic depth and morphological richness on reading processes among typical and dyslexic readers in a within-language design. Methods: 21 typical and 20 poor adult Hebrew readers participated in the behavioral study. 18 typical adult readers participated in the fMRI study. Participants read aloud 248 frequent Hebrew nouns manipulating the following variables: morphological complexity (mono-morphemic vs. bi-morphemic (root+ pattern) nouns); phonological transparency (pointed vs. un-pointed; with vs. without a vowel letter); and word length (3 vs. 4 consonants). Results: Behavioral results show greater reliance on morphological decomposition in dyslexic compared to typical readers. Only dyslexics read pointed words slower than un-pointed words. Both groups benefited from an additional consonant or vowel letter in un-pointed words, whereas the opposite was found in pointed words. The findings from the fMRI study in typical readers showed enhanced activation for pointed words in right fusiform gyrus, consistent with the low familiarity of the orthography, as well as in left pars-opercularis and inferior parietal lobule, indicating enhanced orthography-to-phonology mapping and phonological segmentation. For pointed words greater activation was found in bi-morphemic compared to mono-morphemic words in bilateral middle & superior temporal gyri indicating enhanced semantic and phonological processing. Conclusions: Our results suggest that both typical and dyslexic adult Hebrew readers, reading unambiguous words, do not benefit from increasing the orthographic transparency at the cost of reducing orthographic familiarity. In contrast, they do rely (to different degrees) on morphological decomposition, but not necessarily to compensate for missing phonological information.