Latent semantic analysis of Alzheimer's disease patients' speech as an indicator of semantic network integrity.

摘要

In addition to the hallmark impairment in episodic memory present in Alzheimer's disease (AD), the degradation in previously stored knowledge for words, facts, and concepts (semantic memory) also occurs in this disease. Severity of degradation of semantic memory in AD has been associated with more rapid disease progression and is believed to be reflected in AD patients' difficulty with measures of visual naming, category fluency and other semantically based neuropsychological tests. This project explored the possible use of a novel measure (Latent Semantic Analysis, LSA) to examine this semantic memory degradation in AD patients' verbal description of pictures. The transcriptions of the AD patients' (n = 22) and normal control (NC) participants' (n = 21) speech was used with this internet-based LSA computer program for analysis of semantic content. AD patients completed neuropsychological testing which included a visual naming task (Boston Naming Test) and a number of domains thought to be unrelated to semantic memory functioning. Both AD and NC participants also completed phonemic fluency (FAS) and four semantic fluency tasks of varying category breadth (e.g., animals, breeds of dogs). In the AD patient group, the LSA measure was significantly associated with overall dementia severity as measured by the MMSE, but was not related to estimated rate of cognitive decline. However, contrary to the primary hypothesis of this investigation, the LSA measure was not correlated significantly with any other semantic measure. The AD patients obtained significantly lower LSA scores than the NC participants, but this group difference was relatively small. The other semantic measures were all significantly correlated with each other. Consistent with previous findings, the AD group showed particular difficulty with semantic fluency relative to phonemic fluency. A cut-off score of ⊲ 5 on animal fluency correctly classified 95.4% of the participants. Suggestions were made for possible improvements in methodology using LSA to study the degradation of semantic memory.