Effect of a Conversation Training Therapy–Based Clear Speech Intervention Program (CSIP) on Speech Intelligibility in Parkinson’s Disease

Objectives: To evaluate the effects and maintenance of a Clear Speech Intervention Program (CSIP) on speech-intelligibility and related measures in Parkinson’s disease (PD); and to compare PD outcomes with control group. Methods: Eleven participants with PD (weekly 2 sessions×4 weeks; total 8 sessions) completed Pre, Post, and Follow-up assessments. Acoustic/aerodynamic measures during reading of 10 sentences (Phonatory Aerodynamic System) [PAS 6600] included habitual pitch, pitch range, dB SPL, mean airflow rate (MFR), number of breaths, and speaking rate; perceived fatigue was rated with a 10-cm visual analog scale (VAS). Repeated-measures ANOVAs tested time effects within the PD group. At each time point, the PD group was compared with the control group (N=18) using MANOVA and follow-up univariate tests with Welch adjustments as needed. Results: In the PD group, habitual pitch and pitch range increased significantly from Pre to Post and were maintained at Follow-up; speaking rate decreased at Post and partially rebounded at Follow-up; breaths increased at Post and declined thereafter. Changes in dB SPL and MFR were nonsignificant. Multivariate group differences (PD vs. controls) were significant at all time points, with effect sizes decreasing from Pre to Follow-up, indicating partial gap reduction; pitch metrics normalized to control group levels after intervention, whereas the intensity gap persisted and the PD group remained slower at Post and Follow-up. Fatigue decreased at Post and partially returned at Follow-up; all pairwise comparisons were nonsignificant. Conclusion: A 4-week CSIP produced meaningful improvements in prosody (habitual pitch, pitch range) and adaptive changes in speaking rate and breathing without increasing fatigue. Findings support CSIP as a practical, conversation-based option for enhancing speech intelligibility–related profiles in PD.