Brain responses to morphological processing at pre-school and first grade in children with and without familial risk for dyslexia

Abstract

Typical reading acquisition requires converting written forms (orthography) into a spoken language (phonology) and the ability to manipulate efficiently the smallest meaningful units of language, the morphemes. Dyslexia or difficulties in the acquisition of reading and writing skills, prevent typical reading acquisition and development. Dyslexia is heritable within families; thus, a history of dyslexia within a family could lead to higher chances of the progenies inheriting dyslexia themselves. This dissertation investigates longitudinally the pre-reading linguistic skills of children with and without familial risk for dyslexia. The goal of this dissertation is to investigate language-related processes to correct vs. incorrect morphological constructs in real words and pseudowords, as seen at the brain and behavioral level. Hence, we used magnetoencephalography (MEG) to measure the brain responses of Finnish pre-school (Study I) and first-grade children (Study II) to correctly and incorrectly derived Finnish nouns and pseudo nouns. Additionally, we longitudinally compared the morphological information processing of children at pre-school age (Study I) and later at first grade age (Study II). Then, we aimed to examine how derivational morphology in the Finnish language, concomitant accuracy and reaction times are associated with reading skills in first grade, in addition to the pre-school age reading-related cognitive skills (Study III). Results of Study I showed that both groups of children with and without risk for dyslexia acquired derivational morphology skills, as revealed at the behavioral and brain level, but no differences were observed between the groups with different risk profiles. Results of Study II demonstrated that typically developing children showed sensitivity to morphologically correct vs. incorrect contrast only for real words, while children at-risk for dyslexia showed sensitivity to morphological information processing both for real words and pseudowords. Yet, no significant differences emerged between the two groups. Moreover, Study II revealed significant developmental differences as seen in the behavioral and brain domain when comparing children at pre-school age with children at first grade age for the morphological processing of real words and pseudowords. Last, results of Study III replicated earlier findings; various pre-school cognitive skills were correlated with various first grade cognitive skills. In addition, pre-school children’s reaction time for correctly derived words was correlated with first-grade children’s performance in rapid automatized naming for letters. However, there were no significant correlations between brain activation or behavioral measures of morphological processing and first-grade reading skills. Overall, the findings of this dissertation showed the developmental changes of derivational morphology over time and that derivational morphology, even if it is acquired at pre-school age, does not seem to greatly influence reading acquisition. Further studies are still needed to compare, for example, inflectional and derivational morphology skills in children.