Detection of Vocabulary Delay through Syntactic Complexity in Sentence Comprehension

Objectives: This study investigated the best condition for capturing signs of vocabulary delay in children using the sentence comprehension task (SCT), which consists of active and passive sentence structures with canonical and non-canonical word order conditions; and to determine whether working memory has significant explanatory power for SCT in children with vocabulary delay. Methods: Thirty-two children participated in this study, 16 vocabulary delayed (VD) children and 16 typically developing (TD) children aged 4 to 6 years. Participants completed the SCT, which is designed to focus only on syntactic features by minimizing top-down semantic processing in sentence processing. Four working memory (WM) tasks (Non-word repetition, NWR; Sentence repetition, SR; Digit-forward span, DF; and Digit-backward span, DB) were also administered. Results: The VD group showed greater difficulties in sentence comprehension, especially in the passive-canonical (P-C) condition. However, discriminant analysis results showed that the sum of all conditions in the SCT robustly discriminated these groups. In the VD group, sentence-level WM tasks predicted the passive-canonical (P-C) complex condition in the SCT. Conclusion: The current findings suggest that the VD group had greater difficulty processing more complex sentences, and WM has significant explanatory power for understanding complex syntactic structures in the VD group.