Eye-movement signatures of syntactic development: real-time mapping of passive sentence comprehension in children aged 6–10

Introduction: The ability to understand complex sentences, such as passives, improves during middle childhood. However, it remains unknown when children transition from a "wait-and-listen" strategy to incremental, word-by-word revision of interpretive hypotheses, and whether behavioral accuracy reflects mature online processing. Methods: = 35) process four sentence types (active/passive, direct/reversed word order). Semantic cues were minimized, forcing reliance on morphosyntactic markers. Linear mixed models treated age as a continuous variable to capture fine-grained trajectories. Results: Accuracy improved sharply between ages 7 and 8, with 8-10-year-olds performing at adult levels. However, oculomotor patterns revealed a clear dissociation: at the critical second word in passive direct sentences-where the participle signals thematic role revision-adults and 8-10-year-olds showed a distinct signature (decreased fixation time, increased gaze returns), indicating rapid incremental revision. This signature was absent in 6-7-year-olds, who delayed engagement until the third word. Linear mixed models confirmed that age-related increases in fixation duration were specifically tied to this revision point, extending previous ERP findings that localized revision effects only to the third word. Discussion: Adult-like behavioral accuracy by age 8-10 masks continued immaturity of incremental revision mechanisms. Eye-tracking captures this dissociation, positioning it as a sensitive marker of syntactic development and revealing that the ability to use morphosyntactic cues for real-time revision continues to develop beyond middle childhood.