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 Using eye-tracking in a sentence-picture matching task, we examined how Russian-speaking children aged 6–7 years (n = 16), 8–10 years (n = 16), and adults (n = 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.