Internal and external speech timing mechanisms in persistent developmental stuttering

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

Impaired responses to time-shifting perturbations in adults who stutter during rhythmic and non-rhythmic speech

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Reliability of single-subject neural activation patterns in speech production tasks

Traditional group fMRI (functional magnetic resonance imaging) analyses are not designed to detect individual differences that may be crucial to better understanding speech disorders. Single-subject research could therefore provide a richer characterization of the neural substrates of speech production in development and disease. Before this line of research can be tackled, however, it is necessary to evaluate whether healthy individuals exhibit reproducible brain activation across multiple sessions during speech production tasks. In the present study, we evaluated the reliability and discriminability of cortical functional magnetic resonance imaging data from twenty neurotypical subjects who participated in two experiments involving reading aloud mono- or bisyllabic speech stimuli. Using traditional methods like the Dice and intraclass correlation coefficients, we found that most individuals displayed moderate to high reliability, with exceptions likely due to increased head motion in the scanner. Further, this level of reliability for speech production was not directly correlated with reliable patterns in the underlying average blood oxygenation level dependent signal across the brain. Finally, we found that a novel machine-learning subject classifier could identify these individuals by their speech activation patterns with 97% accuracy from among a dataset of seventy-five subjects. These results suggest that single-subject speech research would yield valid results and that investigations into the reliability of speech activation in people with speech disorders are warranted.Accepted manuscrip

Reliability of single-subject neural activation patterns in speech production tasks

Speech neuroimaging research targeting individual speakers could help elucidate differences that may be crucial to understanding speech disorders. However, this research necessitates reliable brain activation across multiple speech production sessions. In the present study, we evaluated the reliability of speech-related brain activity measured by functional magnetic resonance imaging data from twenty neuro-typical subjects who participated in two experiments involving reading aloud simple speech stimuli. Using traditional methods like the Dice and intraclass correlation coefficients, we found that most individuals displayed moderate to high reliability. We also found that a novel machine-learning subject classifier could identify these individuals by their speech activation patterns with 97% accuracy from among a dataset of seventy-five subjects. These results suggest that single-subject speech research would yield valid results and that investigations into the reliability of speech activation in people with speech disorders are warranted.R01 DC002852 - NIDCD NIH HHS; R01 DC007683 - NIDCD NIH HHS; T32 DC013017 - NIDCD NIH HHSAccepted manuscrip