Objective: This investigation used a single-subject, non-concurrent baseline design to examine the effect of dual-task training (DTT) on vocal intensity levels in three participants with hypophonia secondary to Parkinson’s disease. Method: Vocal intensity levels, measured in decibels (dB), were collected for each participant during a 15-sentence reading and concurrent motor-task. Sound pressure levels in three to seven baseline and 12 intervention sessions were graphed for visual analysis of the data. Three additional speech tasks were assessed in single-task (ST) and dual-task (DT) conditions pre- and post-intervention to measure the interference of a motor-task on vocal intensity (cost-effect). All sessions and data collection were completed via telerehabilitation. Results: All three participants exhibited stability in baseline (averages ranged from 65.3-68.7 dB), followed by an immediate therapeutic increase in volume upon introducing the intervention. Pre-intervention vocal intensity levels were below average but increased to within normal limits post-treatment for all participants. Cost-effect improved with averages in ST increasing between 2.9-18.0 dB and averages in DT increasing between 5.8-18.9 dB for all participants. Conclusion: Visual and data analysis suggested a correlation between DTT and increased vocal intensity. Post-treatment, all participants showed an increase in intensity levels across tasks and ST and DT environments. These results warrant further investigation of DTT for individuals with PD who frequently demonstrate reduced volume while participating in motor tasks.
