Semantics and syntax effects on event-related fields during speech comprehension: a MEG study.

Introduction: Understanding how the brain processes language during natural speech comprehension remains a key challenge. This study tested the feasibility of using an event-related field (ERF) approach to examine the spatiotemporal distribution of brain activity evoked during continuous speech comprehension. Methods: We used MEG and cluster-based permutation analysis of ERFs to examine how semantic dissimilarity and word class modulate neural responses during continuous speech comprehension. Results: Words with high semantic dissimilarity elicited a late ERF effect at left temporal sensors (616-666 ms). This effect remained robust after controlling for word duration and subsequent words. Function words elicited an early ERF (166-312 ms) at left parieto-temporal sensors and a later effect (470-654 ms) at temporal sensors. Discussion: The late effect for words with high semantic dissimilarity may be linked to P600-like activity or other late semantic integration processes. The early and late effects for function words may reflect syntactic processing and the prediction of upcoming words. Together, these findings suggest that semantic dissimilarity and word class differentially shape the temporal dynamics of ERFs during natural speech comprehension.