Syllable Repetition Rates and Intersyllabic Transition Times across Production Phases of Diadochokinetic Tasks in Parkinson’s Disease

Objectives: This study investigated changes in speech characteristics across production phases during diadochokinetic (DDK) tasks to characterize speech motor features in Parkinson’s disease (PD). Unlike previous research that focused primarily on overall speech rate, this study examines articulatory transition ability by measuring intersyllabic transition times across segmented task phases.Methods: Twenty PD patients and twenty age- and gender-matched healthy elderly (HE) adults performed DDK tasks. In addition to the syllable repetition rate, intersyllabic transition times were quantified and compared across the early, middle, and late phases of the task.Results: First, in the alternating motion rate (AMR) tasks, there were no significant differences in the syllable repetition rates between the two groups; however, both groups showed significantly higher repetition rates for /pɑ/ compared to /kɑ/. Second, the PD group exhibited significantly lower syllable repetition rates than the HE group in the sequential motion rate (SMR) task. Third, in the AMR task, there were no significant differences in intersyllabic transition times across phases between the two groups. Fourth, in the SMR task, the PD group exhibited significantly longer intersyllabic transition times than the HE group; furthermore, both groups showed longer transition times in the middle phase compared to the early and late phases.Conclusion: Although the two groups showed comparable performance in single-syllable repetition tasks, the PD group exhibited specific deficits in tasks requiring transitions between different syllables. These findings suggest that measuring intersyllabic transition times in diadochokinetic tasks constitutes an important indicator of speech motor features in patients with Parkinson’s disease.