Altered Auditory Feedback Improves Speech Intelligibility in Individuals Diagnosed with Parkinson's Disease: A Pilot Study

Introduction: The purpose of the current study was to evaluate speech intelligibility and speech rate in individuals with Parkinson's disease using altered auditory feedback (AAF) in comparison to age-matched healthy controls. Based on prior research, it is hypothesized that the use of AAF will improve participants' speech intelligibility. Methods: Five individuals with Parkinson's disease (clinical group) and five age-matched healthy controls aged 50 years and above participated in this pre-/post-group experiment. All participants completed reading and monologue tasks with and without AAF. The AAF delayed the participants' auditory feedback by 150 ms and altered it by 1/20 octave. Thirty-two naive listeners listened to the recorded participants' speech samples (with and without AAF) randomly and rated the participants' speech intelligibility. Results: Results of the mixed model ANOVA revealed that participants in the control group had significantly higher speech intelligibility scores than the participants in the clinical group. Post hoc tests indicated that only participants in the clinical group were more intelligible with AAF than without AAF. Participants in the clinical group had better speech intelligibility when reading the passage than speaking the monologue. With regards to speech rate, participants spoke more slowly with AAF than without. Finally, there was a negative correlation between speech rate and speech intelligibility. Discussion: The current findings support our hypothesis that AAF improves speech intelligibility in people with Parkinson's disease, though not in healthy controls. Future research should evaluate the long-term effect of AAF use on speech intelligibility in people with Parkinson's disease.