The aims of this study were to: 1) compare voicing contrast in speakers with Parkinson disease (PD) and healthy controls by comparing the separation of voice onset time (VOT) distributions of voiced and voiceless stop consonants and 2) to determine whether the administration of dopaminergic medication affected VOT separation in speakers with PD. Data from a previous study by Fisher and Goberman (2010) were used to compare the VOT measures obtained from a group of speakers with PD with both ON and OFF medication, and a group of healthy controls. Supplementing the previous findings, the current analysis revealed that individuals with PD exhibited significantly less contrast between voiced and voiceless VOT than that observed in healthy speakers. Medication administration did not affect VOT contrast as no differences in VOT separation were observed between the ON and OFF medication states.

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Purpose: The purpose of this study was to examine a potential increased cognitive processing bottleneck within Parkinson disease (PD) by extending a previous overlapping task methodology. Additionally, this study extends previous overlapping task methodology in PD to examine the influence of modality (vocal vs. manual) on response delays in overlapping tasks in PD. Method: This study used the psychological refractory period (PRP) paradigm (overlapping-task paradigm) to study processing limitations as participants complete two tasks that increasingly overlap in time. Three levels of temporal overlap of tasks were utilized to vary cognitive demands on manual and vocal response time tasks. Ten participants with PD (PwPD) and 12 participants without PD were included in this study. Results: Participants with PD demonstrated response time delays across temporal overlap conditions (likely indicating motor deficits) along with a larger increase in response delays in the most overlapped, cognitively taxing condition (likely indicating longer central processing bottleneck). Additionally, modality did not influence response times differently in overlapping task conditions or within participant groups. Conclusion: An extension of previous overlapping task methodologies within a complex task was successful in demonstrating an increased central processing deficit across manual and vocal response delays in PD, regardless of modality of response.

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