The effect of Parkinson disease on voice onset time: Temporal differences in voicing contrast

Parkinson disease (PD) affects the basal ganglia, which is involved with the selection, sequencing, and implementation of movement. Investigations suggest an extension of deficits to the speech motor and linguistic systems. Previous studies examining voice onset time (VOT) suggest that VOTs are neither systematically delayed nor systematically advanced in PD as compared to controls. The VOTs for voiced and voiceless stops are expected to differ for both individuals with PD and controls. However, inefficiencies in the sequencing and implementation of the voicing gesture may result in a smaller difference between VOT values of voiced and voiceless cognates. The current study examined VOT in individuals with PD and controls. Participants produced a corpus of stimuli to evaluate VOT using the carrier phrase “CVp again.” The four corner vowels and all stop consonants were used. Speech was recorded and VOT values were manually measured for every utterance. Overall VOTs were significantly shorter for voiceless stops across all speakers. However, the average difference between the voice and voiceless cognates produced by the PD group was significantly smaller than the control group. These data suggest that the PD group exhibited less temporal distinction between voiced and voiceless stops.