Exploring the spatiotemporal dynamics of on-line sentence comprehension in 5-year-olds: The role of semantic context in syntactic processing and behavioral correlates of MEG-recorded brain activity

Thesis (Ph.D.)--University of Washington, 2020Despite evidence that the neural mechanisms underlying syntactic and semantic operations develop early in life, these processes are believed to remain functionally interdependent until much later in childhood. However, the nature of the dynamic interplay between syntax and semantics during on-line language comprehension in children is not well understood. While language and brain development are ongoing, children may rely on the availability of lexical-semantic information for syntactic processing and vice versa. Furthermore, the processing strategies children use to understand complex linguistic input may vary with their language skills. This study aims to advance the current knowledge of sentence processing in the developing brain, and to investigate relationships between children’s language proficiency and sentence processing ability at kindergarten onset. Magnetoencephalography (MEG) was used to record typically developing 5-year-olds’ brain responses to syntactic manipulations in meaningful and semantically impoverished sentences. Correlations were performed between MEG-recorded brain activity in each condition and prospective and concurrent behavioral language measures. Results showed that the neural signatures of on-line sentence processing in 5-year-olds are indeed modulated by the availability of lexical-semantic information for grammatical parsing: phrase structure violations in meaningful sentences elicited a syntactic processing effect in the left hemisphere, whereas intact phrase structure in meaningless sentences elicited an attentional effect in the right hemisphere. These qualitative differences in cortical activation to manipulations of syntax and semantics support the hypothesis that there is a protracted developmental period in which these processes remain functionally interdependent. Enhanced attention to grammatically congruent meaningless sentences may signify an important language learning mechanism and index of processing efficiency, associated with language skill; indeed, children with higher scores on behavioral measures of language development and proficiency attended more strongly to the salient structural features of language when lexical-semantic information was absent. These findings provide novel information about the dynamics of on-line sentence comprehension during development, and contribute to our understanding of processing strategies children may use to navigate complex linguistic environments