Fundamental frequency as a perceptual cue for vowel identification in speakers with Parkinson's disease

This study investigates the importance of fundamental frequency (F0) as a perceptual cue for identification of vowel targets produced by speakers with Parkinson's disease (PD). It has been suggested in the literature that F0 is a redundant cue for vowel identification in highly intelligible speech. For speakers with dysarthria who are having difficulty with segmental and suprasegmental aspects of production which result in ambiguous or conflicting cues in the acoustic signal, F0 may have increased perceptual importance for accurate identification of vowel targets. In the present study, F0 contours for single-word targets produced in sentence level material by 20 speakers with PD and 20 control speakers were synthetically modified in several different ways (i.e., flattened and enhanced). Listener identification of vowel targets across the F0 conditions was recorded. The accuracy of vowel identification for the control group was not affected by the flattening of the F0 contour. For the speakers with PD, however, modification of the F0 contour (flattening or enhancing) affected the accuracy with which listeners identified certain vowels. Differences in vowel identification were found primarily for the front vowels /I, epsilon, ae/ along a high-low continuum.