Electronic Thesis and Dissertation Repository

Thesis Format



Doctor of Philosophy


Health and Rehabilitation Sciences


Adams, Scott G.


Hypophonia (low speech intensity) has been found to be the most common speech symptom experienced by individuals with Parkinson’s disease (PD). Previous research suggests that, in the PD population, there may be abnormal integration of sensory information for motor production of speech intensity. In the current study, auditory feedback was systematically manipulated during sensorimotor conditions that are known to modulate speech intensity in everyday contexts. Twenty-six individuals with PD and twenty-four neurologically healthy controls were asked to complete the following tasks: converse with the experimenter with varying distances between the participant and listener (near and far distances), vowel prolongation, read sentences at a comfortable loudness, complete a magnitude production task (reading 2 times louder, 4 times louder, maximum loudness), and complete an imitation task (50dB, 60dB, 70dB, 80dB), while hearing their own speech intensity randomly altered. Altered intensity feedback conditions included 5, 10 and 15dB reductions and increases in the feedback intensity. Participants were also asked to read sentences with and without an instruction to attempt to ignore the auditory feedback. Speech tasks were completed in no noise, background noise, and a complete masking noise condition. Outcome measures included speech intensity (dB) and loudness perception ratings obtained using a visual analogue scale. Overall results indicate that individuals with PD display a reduced response to the altered intensity feedback in all speech tasks, suggestive of abnormal of processing of auditory feedback for speech intensity regulation. Specific deficits related to the perception of self-loudness are suggested based on the current findings. Clinical implications are discussed as they relate to understanding specific deficits of auditory processing for speech impairments in PD.

Summary for Lay Audience

Approximately 80% of individuals with Parkinson’s disease (PD) experience low speech intensity. Previous researchers have shown this speech problem has a negative impact on overall quality of life. The cause of this speech problem is unclear and this prevents appropriate therapy development. Producing speech intensity that is appropriate when communicating with others is a complex process, which involves regulating self-produced speech intensity, monitoring ambient or background noise in the surroundings, and maintaining speech loudness throughout a conversation. It is possible that the low speech intensity produced by individuals with PD is caused by a problem related to how they perceive the loudness of their own speech. To examine this potential cause, the current study systematically manipulated how individuals hear their own speech by altering auditory feedback. Testing involved making an individual’s speech sound louder than was actually being produced and sometimes quieter than was actually being produced. Previous research suggests that healthy speakers compensate for this type of manipulation by producing speech in the opposite direction. For example, when an individual’s speech is manipulated to sound louder than is actually being produced, the speaker typically adjusts their speech to be quieter. This testing was conducted while individuals were being asked to complete a variety of speech tasks typically encountered in daily life, such as in conversation and while speaking in background noise. Results from twenty-six individuals with PD and twenty-four neurologically healthy participants found that individuals with PD made significantly smaller adjustments in their speech intensity during altered auditory feedback conditions compared to the non-neurologically impaired participants. These findings suggest that in PD, there may be abnormal perception of the sound of their own speech and this abnormality may be related to the cause of their low speech intensity. Findings from this study are anticipated to impact how clinicians treat the speech problems in PD and may lead to the development of new therapeutic techniques.