Abstract
PURPOSE: The purpose of the current study was to investigate the effect of increased vocal intensity on interarticulator timing in individuals with Parkinson's disease (PD). METHODS: Ten individuals with mild to moderate hypophonia, secondary to PD, were selected for study. Over an 8-week treatment period, multi-talker babble noise was presented monaurally to the individuals with PD during everyday communication contexts to elicit increased vocal intensity (Lombard effect). Outcome measures included sound pressure level (SPL), voice onset time (VOT), VOT ratio, percent voicing, and speech intelligibility. RESULTS: Group and individual participant responses to the treatment are reported and discussed. Speakers with PD were shown to significantly increase SPL in response to treatment. Six of the 10 speakers showed improved temporal coordination between the laryngeal and supralaryngeal mechanisms (interarticulator timing) in response to treatment. Four of the 10 speakers, however, showed reduced laryngeal–supralaryngeal timing at the end of treatment. Group speech intelligibility scores were significantly higher post-treatment as compared to pre-treatment. CONCLUSIONS: Voice treatment during everyday communication resulted in improved temporal coordination across the laryngeal and supralaryngeal mechanisms for the majority of speakers with PD and made them easier to understand. Further investigations are planned to explore individual differences in response to treatment. The identification of speaker-specific voicing and devoicing strategies is consistent with the heterogeneous nature of PD. LEARNING OUTCOMES: Readers will be able to: 1. Describe the speech and voice characteristics of individuals with Parkinson's disease. 2. Define the Lombard effect. 3. Describe acoustic measures of voice onset time and percent voicing. 4. Describe the effect of voice treatment on voice onset time and percent voicing in individuals with Parkinson's disease.