The effects of intensive speech treatment on intelligibility in Parkinson’s disease: A randomised controlled trial

Levy, E. S., Moya-Galé, G., Chang, Y. M., Freeman, K., Forrest, K., Brin, M. F., & Ramig, L. A. (2020). The effects of intensive speech treatment on intelligibility in Parkinson’s disease: a randomised controlled trial. The Lancet’s EClinicalMedicine, 24, 100429.

What is it about?

This article reports on a randomized controlled trial (RCT) examining the effects of intensive speech treatment on speech intelligibility in 57 patients with Parkinson’s disease (PD). One group of patients with PD received treatment targeting voice (LSVT LOUD®), a second received treatment targeting articulation (LSVT ARTIC™), and a third group received no treatment (NO TX). Before and after treatment, the patients were audio-recorded describing a time when they felt extremely happy, to control for emotional content in speech. We played the recordings to 117 listeners, who transcribed (typed) what the patients were saying. Intelligibility was measured by examining the percentage of words the listeners transcribed correctly. Results showed that only the treatment targeting voice improved speech intelligibility significantly (by 31.5%), suggesting that LSVT LOUD helps patients with PD communicate more successfully.

Why is it important?

Randomized controlled trials (RCTs) are the gold standard of evidence for treatment efficacy. Previous studies had shown that treatment targeting voice results in short-term and long-term improvements across many aspects of PD, including vocal loudness, swallowing disorders, and articulation. However, while intelligibility is essential for speech communication, the question of whether speech becomes more intelligible after treatment had not been investigated in an RCT. Furthermore, reduced vocal loudness is one of the first and most common problems in PD, reducing audibility, and often intelligibility. Therefore, it is critical to include vocal loudness in measures of intelligibility pre- and post-treatment. This is the first RCT that has included the dimension of vocal loudness in measuring speech intelligibility in PD pre- and post-treatment. Our results strongly support the implementation of treatment targeting voice for increasing intelligibility. And this was narrative speech, in all its complexity, more closely mimicking patients’ daily speech than does the read or repeated speech often examined in speech treatment studies. Additionally, we hope that our methodological advances, such as examining narrative speech, measuring transcription accuracy (the gold standard measure of intelligibility), controlling emotional content in speech, including two treatment comparators (two active and one inactive control), and including the dimension of patients’ vocal loudness in intelligibility measurement, will help inspire further rigorous treatment research in the field.


For additional perspectives on this treatment study and line of treatment research, we asked lead researchers and co-authors on this study Drs. Erika Levy and Lorraine Ramig a few questions. Their insights are provided below.

Why did you want to study speech intelligibility following a voice treatment?

When we speak to someone, our goal is to be understood. One of the most devastating aspects of Parkinson’s disease is that it affects speech production, often reducing intelligibility and resulting in poor communication and social isolation. Although many positive effects of LSVT LOUD are known, it was crucial to find out and document, using rigorous methodology, whether patients become more intelligible following this treatment.

How might this impact SLPs who are working with people with Parkinson’s disease?

Combined with improvements in aspects of speech production such as vocal loudness, swallowing disorders, intonation, articulation and communicative efficiency reported in previous studies, our findings suggest that SLPs’ patients with PD will experience improvements in speech communication and quality of life if treatment targeting voice is included in the patients’ care plan.

“The continued focus on high-quality LSVT LOUD research is a testament to the pursuit of science and understanding of “if”, “how”, and “why” speech treatment for people with Parkinson’s disease works. This knowledge allows us to further advance treatments with the goal of making them even more effective. The work of Dr. Levy, Dr. Ramig and the other authors of this study has once again advanced LSVT LOUD research in innovative ways to provide the first RCT examining speech intelligibility in people with PD.”

– Cynthia M. Fox, PhD, CCC-SLP, CEO LSVT Global, Inc.

Were there any surprises or key things you learned?

It was somewhat surprising to find that, even though we typically associate greater intelligibility with greater articulation, the treatment targeting articulation didn’t improve speech intelligibility significantly, whereas treatment targeting voice did. This suggests that when patients with PD increase their vocal loudness, their intelligibility increases both because of their vocal loudness increase and because this increase spreads across speech subsystems, improving speech production in intelligibility-enhancing ways overall.

What is happening next in terms of your research on LSVT LOUD?

We are examining the longer-term effects of LSVT LOUD on intelligibility in patients with PD. We are also investigating the associations between post-treatment changes in loudness and in intelligibility. Additionally, we are exploring short- and long-term effects of LSVT LOUD on intelligibility across languages, with studies on Mandarin and Spanish in progress. Future research includes the examination of effects of LSVT LOUD on intelligibility in a variety of populations, such as individuals with Down syndrome, cerebral palsy, ataxia, or multiple sclerosis.

Download the full article abstract and citation HERE.


  1. Watch our on-demand webinar Cross-linguistic exploration of LSVT LOUD for Parkinson’s disease: Is a universal speech treatment approach plausible?: What you need to know HERE
  2. View LSVT LOUD References HERE
  3. Read our blog on Improving speech in individuals with Parkinson’s disease HERE

About the Authors

Erika S. Levy, Ph.D., CCC-SLP

is Associate Professor of Communication Sciences and Disorders and Director of the Speech Production and Perception Lab at Teachers College, Columbia University. Professor Levy publishes in the areas of treatment efficacy for the motor speech disorder of dysarthria across languages in children with cerebral palsy and adults with Parkinson’s Disease, with a focus on intelligibility. She has received funding from the National Institutes of Health and ASHFoundation, among other sources.


Lorraine Ramig, Ph.D., CCC-SLP

pioneered the Lee Silverman Voice Treatment (LSVT) for persons with Parkinson’s disease, and spearheaded over 25 years of research funded by the National Institutes of Health (NIH) and other organizations to support its development, efficacy studies, and implementation. As Chief Scientific Officer (CSO) at LSVT Global, Inc., she continues to direct research in LSVT LOUD and is faculty for LSVT LOUD training and certification courses. She received her doctorate from Purdue University and has been a Professor in the Department of Speech, Language, and Hearing Science at the University of Colorado-Boulder, Senior Scientist at the National Center for Voice and Speech in Denver, and Adjunct Professor at Columbia University. Dr. Ramig holds Honors and is a Fellow of the American Association of Speech-Language Pathologists and Audiologists (ASHA), in addition to many other awards and honors. She was born and raised in northern Wisconsin and currently resides in New York City.