Improvement of voicing in patients with Parkinson's disease by speech therapy.

Speech therapy in PD patients, focusing on an increase of phonatory-respiratory effort, has adverse effects because it raises vocal pitch and laryngeal muscle tension. The authors' approach, the Pitch Limiting Voice Treatment (PLVT), increases loudness but at the same time sets vocal pitch at a better level. In this study, the Lee Silverman Voice Treatment ("think loud, think shout") and PLVT ("speak loud and low") are compared. Both treatments produce the same increase in loudness, but PLVT limits an increase in vocal pitch and prevents a strained or pressed voicing.