The effects of Parkinson’s disease on the production of contrastive stress

Abstract

Reduced speech intelligibility has been observed clinically among patients with Parkinson’s disease (PD); one possible contributor to these problems is that motor limitations in PD reduce the ability to mark linguistic contrasts in speech using prosodic cues. This study compared acoustic aspects of the production of contrastive stress (CS) in sentences that were elicited from ten subjects with PD and ten matched control subjects without neurological impairment. Subjects responded to questions that biased them to put emphasis on the first, middle, or last word of target utterances. The mean vowel duration and mean fundamental frequency (F0) of each keyword were then measured, normalized, and analyzed for possible differences in the acoustic cues provided by each group to signal emphatic stress. Both groups demonstrated systematic differences in vowel lengthening between emphasized and unemphasized words across word positions; however, controls were more reliable than PD subjects at modulating the F0 of emphasized words to signal its location in the utterance. Group differences in the F0 measures suggest one possible source of the impoverished intelligibility of Parkinsonian speech and will be investigated in a subsequent study that looks at the direct impact of these changes on emphasis perception by listeners. [Work supported by CIHR.]