The effect of increased vocal intensity on interarticulator timing in speakers with Parkinson’s disease: a preliminary analysis

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.

Figures

Figure 1

Mean SPL with standard error bars shown for ten speakers with Parkinson’s disease. The asterisk (*) indicates significant comparisons at an alpha of 0.05. SPL data is indicated for pre-treatment (PreAvg), the onset of post-treatment (PTWK1), and 4-weeks post-treatment (PTWK4). The treatment effect = PTWK1-PreAvg. The detraining effect= PTWK4-PTWK1.

Figure 2

Figures 2a–c. Mean voice onset time (VOT) data shown by place of articulation for the six individual speakers who demonstrated improvement in VOT with treatment. Data is shown for pre-treatment average (PreAvg), immediate post-treatment (PTWK1) and 4-weeks post-treatment (PTWK4). The treatment effect = PTWK1- PreAvg. The detraining effect= PTWK4- PTWK1. Horizontal line = mean VOT data reported for nine healthy older adult speakers by Fischer and Goberman (2010) for word-initial [p] [t] [k]. Voicing boundary at 25 msec for production of word-initial English stop consonants (Lisker & Abramson, 1964).

Figure 3

Figures 3a–c. Mean voice onset time (VOT) data shown for the four individual speakers who did not demonstrate improvement in VOT with treatment. Data is shown for pre-treatment average (PreAvg), immediate post-treatment (PTWK1) and 4-weeks post-treatment (PTWK4). The treatment effect = PTWK1- PreAvg. The detraining effect= PTWK4- PTWK1. Horizontal line = mean VOT data reported for nine healthy older adult speakers by Fischer and Goberman (2010) for word-initial [p] [t] [k]. Voicing boundary at 25 msec for production of word-initial English stop consonants (Lisker & Abramson, 1964).

Figure 4

Figures 4a–c. Illustration of laryngeal and supralaryngeal adjustments associated with post-treatment increases in vocal intensity during production of vocalic to voiceless stop sequences. Data is shown for the six individual speakers from Figure 2and are pooled across place of articulation. Percent voicing is indicated for each session: pre-treatment average (PreAvg), immediate post-treatment (PTWK1), and 4-weeks post-treatment (PTWK4). The treatment effect = PTWK1-PreAvg. The detraining effect= PTWK4-PTWK1.

Figure 5

Illustration of laryngeal and supralaryngeal adjustments associated with post-treatment increases in vocal intensity during production of vocalic to voiceless stop sequences. Data are shown for the four individual speakers from Figure 3 and are pooled across place of articulation. The percent voicing is indicated for each session: pre-treatment average (PreAvg), immediate post-treatment (PTWK1), and 4-weeks post-treatment (PTWK4). The treatment effect = PTWK1-PreAvg. The detraining effect= PTWK4-PTWK1.

Figure 6

Mean speech intelligibility scores shown by speaker group: “Improved”, “Unimproved”, and all speakers combined (Improved + Unimproved). “Improved” speakers demonstrated a favorable change in interarticulator timing in response to voice treatment. “Unimproved” speakers demonstrated an unfavorable or unremarkable change in interarticulator timing in response to voice treatment. Data is shown for pre-treatment (Pre) and immediate post-treatment (PTWK1). The treatment effect = PTWK1-PreAvg. The detraining effect= PTWK4-PTWK1.