Ataxic dysarthria is a disorder affecting the naturalness of speech due to damage to the cerebellum, a neural structure critical for the timing, scaling, and sequencing of speech movements (Ackermann, Vogel, Petersen, & Poremba, 1992; Diener & Dichgans, 1992; Duffy, 2013; Rampello, Rampello, Patti, & Zappia, 2016). In healthy individuals, the cerebellum facilitates speech naturalness by integrating sensory feedback (auditory and somatosensory) with cortical motor plans for speech (Ackermann et al., 2007; Duffy, 2013; Spencer & Rogers, 2005). This sensorimotor integration allows the cerebellum to adjust the temporal and prosodic properties of the motor plans according to the current muscular and phonetic environment of the speech production system. These adjustments result in smooth, coordinated speech movements. When cerebellar functioning is diminished in ataxic dysarthria, prosody is impaired because the production of pitch, loudness, and articulation are imprecise, poorly timed, and uncoordinated (Darley, Aronson, & Brown, 1969). Although the cerebellar dysfunction for sequencing sounds and words in ataxic dysarthria is known (Spencer & Rogers, 2005), at the present, little is known for how impaired sensorimotor integration in the cerebellum impacts naturalness for prosodic production. The goal of this dissertation is to characterize the deficits in sensorimotor integration in ataxic dysarthria to better understand the underlying mechanisms for prosodic impairment in speech production. We hypothesize that the reduced naturalness in ataxia is due to prosodic impairment resulting from disrupted feedback control by neural circuits involving the cerebellum. More specifically, we theorized that ataxia results in a diminished ability to integrate sensory feedback with (i) prior motor plans for speech, affecting reflexive corrective mechanisms for intonation, as well as (ii) future motor plans for speech, affecting predictive scaling mechanisms for adjusting downstream intonational targets. Inherent in this hypothesis is that sensorimotor integration is vital for both reflexive and predictive response mechanisms for intonation. Healthy speakers make reflexive, rapid vocal responses to pitch auditory feedback perturbations in order to maintain a steady F0 (Burnett, Freedland, Larson, & Hain, 1998), and they enhance the acoustic properties of a phrase-final prominent word (i.e. pitch accent) after a perturbation earlier in the phrase (Hilger, Cole, Kim, Lester-Smith, & Larson, in press). Reflexive responses during steady vocalization demonstrate a corrective mechanism for sensory integration with prior motor plans. Adjustments to downstream pitch accents in phrase production demonstrate a predictive mechanism to adjust upcoming intonation targets based on feedback of the current prosodic environment of the phrase. In this dissertation, we demonstrate that auditory feedback control is impaired in ataxia because of over-corrected reflexive responses and impaired sensory prediction to scale phrasal stress. Overall, the goal for this research is that understanding the sensorimotor integration impairment in ataxic dysarthria will allow us to develop more effective therapy techniques for enhancing speech naturalness and intelligibility.

Creator

• Hilger, Allison Ilice

DOI

• https://doi.org/10.21985/n2-thj4-vq36

Subject

• Speech therapy
• Linguistics
• Acoustics

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:15086
• etdadmin_upload_742085

Keyword

• Ataxia
• Auditory Feedback
• Pitch-shift
• Dysarthria
• Prosody
• Pitch

Date created

• 2020-01-01

Resource type

• Dissertation

Rights statement

• In Copyright