Semantic dependency network approach to the lexico-semantic impairment of Mandarin-speaking patients with probable Alzheimer’s dementia

Background Population ageing has increased dementia prevalence in China, and language impairments represent a prominent behavioral manifestation of cognitive decline.Aims Compared with healthy controls (HCs), this study aims to explore mainland Chinese probable Alzheimer’s dementia (PAD) patients in three aspects: (1) the distribution of semantic dependencies, (2) how PAD patients use lexical items and semantic relations to construct event representations, and (3) semantic connection strength in their connected speech.Methods & Procedures This study analyzed the semantic dependency treebanks and networks of the Cookie Theft Picture descriptions from 50 age-, gender- and education-matched Chinese Mandarin-speaking PAD (mean MoCA = 17.44) and 50 HCs (mean MoCA = 26.02).Outcomes & Results (1) Oral production in PAD patients featured a smaller variety of semantic dependency relations than HCs. (2) PAD patients exhibited simplified and direct event interpretation and construction, while HCs employed flexible, comprehensive, and multi-layered event processing. (3) PAD and HC groups exhibited notable differences in their high in-degree nodes: the former was dominated by content words (e.g. 这个 zhège “this”, 在 zài “aspectual adverb”, 他 tā “male”), while the latter was primarily characterized by function words (e.g. 的 de, “structural particle”, 了 le “aspect marker”, 在 zài “aspectual adverb”). In contrast, both groups share key out-degree nodes: 是 shì “be”, 拿 ná “take” and 洗 xǐ “wash”. In the PAD group, representative high-weighted node pairs reflect core thematic relations such as Experiencer, exemplified by (是 shì “be”, 这个 zhège “this”), whereas HCs feature Patient as in (洗 xǐ “wash”, 碗 wǎn “dishes”); for functional grammatical markers, PAD patients use mTime (time marker) while HCs employ mNeg (negation marker), represented respectively by (洗 xǐ “wash”, 在 zài “aspectual adverb”) and (知道 zhīdao “know”, 不 bù “not”).Conclusions These findings reveal that PAD patients exhibit multi-level deficits across visual-semantic comprehension, semantic memory access and lexical retrieval during connected speech production, and semantic dependency network analysis offers a quantitative approach to characterize such language impairments.