Vowel contrasts relative to schwa across tasks: Preliminary findings for Parkinson’s disease

Abstract

The purpose of this study is to quantify acoustic contrasts of vowels in relation to the mid-central unrounded vowel schwa produced by speakers with Parkinson’s disease (PD) in different speaking tasks. The study is motivated by a hypothesis that schwa may serve as a speaker-specific reference for vowel contrasts given its associated anatomical properties of a neutral vocal tract. For the present study, a speaker-specific reference schwa is identified from averaged first and second formant (F1 and F2) frequencies of unstressed article “a” productions in citation form. Two questions are addressed. First, can speaking-task related changes in vowel contrasts be expressed by vowel-schwa distances in the acoustic space consistently across speakers? Second, do characteristics of schwa-referenced vowel contrasts differ for speakers with PD and healthy speakers? F1 and F2 frequencies of schwa and vowels /i/, /a/, and /u/ in three tasks including clear-speech, sentence reading, and passage reading are examined. The Euclidean distance between each vowel and schwa is evaluated for a given speaker across tasks. It is hypothesized that the within-speaker distances between vowels and schwa are task-sensitive in the direction of clear-speech to passage reading. Preliminary findings will be discussed within the framework of the acoustic theory and the Hyper- and Hypo-speech theory.