Reduction of vowel space in Alzheimer's disease.

Reduced vowel space area (VSA) is a known effect of neurodegenerative diseases such as Parkinson's disease (PD). Using large publicly available corpuses, two experiments were conducted comparing the vowel space of speakers with and without Alzheimer's disease (AD) during spontaneous and read speech. First, a comparison of vowel distance found reduced distance in AD for English spontaneous speech, but not Spanish read speech. Findings were then verified using an unsupervised learning approach to quantify VSA through cluster center detection. These results corroborate observations for PD that VSA reduction is task-dependent, but further experiments are necessary to quantify the effect of language.