Many people suffering from Parkinson’s disease will at some point notice or experience increasing difficulty with speech production.  Hypophonia (softness of speech) is a common condition occurring in those with Parkinson’s disease (Clark et al., 2014, 1).  Recent studies have suggested that a cause of this condition may have to do with a sensory deficit relating to loudness perception – that is, an impairment in the ability to accurately assess vocal intensity and volume (Clark et al., 2014, 9).
When compared to a control group (individuals selected who do not present with Parkinson’s disease), those with Parkinson’s were found to perceive sound at different volume intensities than those in the control group.  During a magnitude estimation test, participants were asked to listen to a playback of their own voice and rate how loud they thought they were speaking. Those with Parkinson’s disease consistently overestimated the volume of their own voice.  Ho et al. (2000) suggests this discrepancy is a result of “sensorimotor integration disorder”– which involves abnormal perception of one’s own loudness and speech intensity (Clark et al., 2014, 8).

Possibilities for treatment exercises and vocal training:

This study suggests that the ability to increase voice intensity may not be the issue behind hypophonia, but the ability to judge one’s vocal intensity.  Thus, certain forms of training and vocal exercise are in some cases very beneficial to those with hypophonia secondary to Parkinson’s disease.

Behavioural treatment involves simply providing cues to prompt one with hypophonia to speak louder- this increased vocal effort usually improves voice quality, articulation and speech intelligibility (Richardson et al., 2014, 45).

Additionally, Richardson et al. (2014) has found that the Lombard effect is a useful technique in prompting increased vocal intensity, and training the muscles for a longer-term improvement.  This treatment involves introducing noise, which automatically and unconsciously prompts individuals to speak louder, increasing vocal intensity with the intention of training the muscles to perform at this intensity and volume more consistently.

Written by: Kimberly Thomson, Head of Research at Simone Friedman Speech-Language Services.


Clark, Jenna P., et al.  (2014).  Loudness perception and speech intensity control in Parkinson’s disease.  Journal of Communication Disorders, 51, 1-12.

Richardson, Kelly, Joan E. Sussman, Elaine T. Stathopoulos, Jessica E. Huber.  (2014).  The effect of  increase vocal intensity on interarticulator timing in speakers with Parkinson’s disease: a preliminary analysis.  Journal of Communication Disorders, 52, 44-64.