Nouns and Verbs Identify Different Subtypes of MCI

Abstract

It is well-documented that patients with semantic dementia and Alzheimer’s disease present with difficulty in lexical retrieval and reversal of the concreteness effect in nouns and verbs. Little is known about the lexical phenomena before the onset of symptoms. We anticipate that there are linguistic signs in the speech of people who suffer from mild cognitive impairment (MCI), the prodromal stage of dementia. Here, we report the results of a novel corpus-linguistic approach to the early detection of cognitive impairment. We recorded 40 hours of natural, unconstrained speech of 188 English-speaking Singaporeans; 90 are diagnosed with MCI (51 amnestic, 39 nonamnestic), and 98 are cognitively healthy. The recordings yield 327,470 words, which are tagged for parts of speech. We calculate the per-minute speech rates and concreteness scores of nouns and verbs, and of all tagged words, in our dataset. Our analysis shows that the two measures of nouns and verbs identify different subtypes of MCI. Compared with healthy controls, subjects with amnestic MCI produce fewer but more abstract nouns, whereas subjects with nonamnestic MCI produce fewer but more concrete verbs. Cognitive impairment is manifested in ordinary language before the presentation of clinical symptoms, and can be detected through non-invasive corpus-based analysis of natural speech.