Internal and external speech timing mechanisms in persistent developmental stuttering

• Main Author: Frankford, Saul Alexander
• Other Authors: Guenther, Frank H.
• Language: en_US
• Published: 2021
• Subjects: Neurosciences
• Online Access: https://hdl.handle.net/2144/42559

Stuttering is a developmental speech disorder characterized by interruptions of fluency. A large body of research suggests that stuttering occurs due to a reduced ability to generate timing signals in order to sequence speech sounds. One piece of supporting evidence for this is that when speaking along with an external timing source like a metronome, disfluencies suddenly and significantly decrease. The aim of this dissertation was to characterize the effects of using auditory cues to time speech on neural activation and auditory feedback processing, and how these effects may contribute to fluency in adults who stutter (AWS). Two studies were carried out to examine these effects. In the first study, functional magnetic resonance imaging was used to measure brain activity while AWS and adults who do not stutter (ANS) read sentences aloud either using natural speech timing or aligning each syllable to the beat of a metronome. Consistent with previous literature, AWS produced fewer disfluent trials in the externally paced condition than in the normal condition. Collapsing across the AWS and ANS groups, participants had greater activation in the metronome-timed condition in regions associated with speech sequencing, sensory feedback control, and timing perception. AWS also demonstrated increased functional connectivity among cerebellar regions during externally paced speech. In the second study, responses to online spectral and timing perturbations of auditory feedback were measured while AWS and ANS read sentences with and without metronome pacing. Results indicated that AWS showed no responses to spectral perturbations during the non-paced condition and significant compensatory responses during the paced condition along with fewer disfluencies, while responses in ANS showed the opposite effect. For the timing perturbation, no significant differences were found between groups in either condition. Together, these studies indicate that the deficit in stuttering is related to spectral processing rather than purely temporal processing, and that externally paced speech recruits compensatory neural regions that may help resolve this deficit.