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Neural dynamics during morphological processing in Hebrew reading: a comparative study of dyslexic and typical readers
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Tali Bitan1, Batiah Keissar*1, Eva Kimel*2, Sagi Jaffe-Dax3, Merav Ahissar4; 1University of Haifa, 2University of York, 3Tal Aviv University, 4Hebrew University
Developmental dyslexia is commonly associated with deficits in phonological awareness, however, studies showing impairments also in non-linguistic tasks in these individuals suggest that the underlying deficit may be more domain general (Ullman et al., Annual Review of Psychology, 2020). Morphological processing is crucial for reading development in both dyslexic and typical readers across orthographies. Morphological processing also plays a central role in reading Hebrew, a morphologically rich language, where most words are formed by combining roots and patterns. While imaging studies show that dyslexic Hebrew readers exhibit enhanced morphological effects in the Fusiform gyrus (Bitan et al., Cortex, 2020), behavioral studies of dyslexic readers also show deficits in learning and benefiting from morphological regularities (Ben-Zion et al., Neuropsychologia, 2023; Kimel et al., Neuropsychologia, 2020). One possible explanation for these morphological deficits in readers with dyslexia, is their decreased ability to benefit from regularities in previously encountered stimuli (Ahissar, TICS, 2007; Jaffe-Dax et al., eLife, 2018). Indeed, neuroimaging studies show attenuated neural adaptation for repeating stimuli in Dyslexic readers across multiple stimulus types, including written word stimuli in the Fusiform gyrus (Perrachione et al., Neuron, 2016). The current study examined whether impaired morphological sensitivity in dyslexic readers can be explained by attenuated neural adaptation to morphologically related words. Thirty-nine Hebrew speakers (20 dyslexic, 19 typical) were scanned using fMRI in five conditions, each comprised of blocks of 6-word lists: Identical (6 repetition of the same word), Root (6 words that share a 3-consonant root), Letters (6 words sharing 3 letters which are not part of the root), Unrelated (6 unrelated words), and Symbols. While reading these lists of words, participants were asked to count words with larger fonts. The region of interest (ROI) for our analysis was defined based on voxels showing decreased activation between the first and second halves of the blocks across all conditions. It was located in the left Fusiform gyrus and contained the Visual Word Form Area (Dehaene & Cohen, TICS, 2011). Our analysis showed a three-way interaction between condition, block-half and phonological ability. Follow-up analysis showed a positive correlation between phonological awareness and the extent of the neural adaptation in the fusiform gyrus during the morphological (root) condition. This correlation was not evident for any of the other lexical conditions. These findings suggest that readers with poor phonological abilities exhibit attenuated neural adaptation during morphological processing which implies that they may struggle to efficiently recognize and process morphemic units (like roots) that are critical for fluent reading. Moreover, this weaker attenuation to morphologically-related stimuli was independent of a formal dyslexia diagnosis. Furthermore, the presence of this correlation in the Fusiform gyrus suggests that this deficit is already in effect during early stages of orthographic processing.
Topic Areas: Disorders: Developmental, Morphology