Doctor of Philosophy
Communication Sciences & Disorders
David Kimbrough Oller
Speech rhythms play important roles in facilitating effective communication. This dissertation aimed to examine the neuro-behavioral synchrony related to hierarchical speech rhythms. Study #1 investigated relations between entrainment in the perceptual and production domains by measuring individuals’ brain oscillatory tracking to speech (EEG) and their simultaneous and non-simultaneous vocal productions synchronized to syllable rates between 2.5 and 8.5 Hz. We show that neural oscillations flexibly phase lock to speech in a rate-dependent manner, but is boosted near ∼4.5 Hz, the dominant syllable rate. Cued speech productions (recruiting sensorimotor interaction) were optimal between 2.5 and 4.5 Hz, suggesting a low-frequency constraint on sensorimotor integration. Contrarily, “pure” motor productions (without concurrent sound cues) were most precisely generated at rates of 4.5–5.5 Hz, paralleling the neuroacoustic tracking. Notably, individuals demonstrating stronger auditory-perceptual entrainment exhibited better synchronization with speech rhythms motorically, supporting an intimate link between exogenous and endogenous rhythmic processing that is optimized at 4–5 Hz in both auditory and motor systems. Study #2 extended Study #1 to examine how neural oscillations code the hierarchical nature of stress rhythms depending on language experience. By measuring multilevel EEG-acoustic synchrony and intra-brain cross-frequency phase coupling, we show encoding of stress involves different EEG signatures (delta rhythms = stress rate; theta rhythms = syllable rate), is stronger for amplitude vs. duration stress cues, and induces nested delta-theta coherence that reflects the stress-syllable hierarchy in speech. English speakers exhibited enhanced synchronization at the central stress (2 Hz) and syllable (4 Hz) rates intrinsic to natural English suggesting plasticity in stress processing. Significant group differences across English and Mandarin speakers emphasize that the brain-speech enhancement is not purely a “bottom-up” response but is improved by “top-down” processing rooted in listeners’ language-specific knowledge. Critically, English individuals with superior cortical-acoustic stress tracking capabilities also displayed pronounced neural hierarchical coherence, highlighting a nuanced interplay between internal neural coherence and external entrainment. Collectively, our studies reveal intricate relationships between synchronization in the auditory and motor systems (i.e., neural oscillations) and multilevel speech rhythms and highlight the critical role of brain oscillations in tracking and encoding speech rhythms hierarchically and language-dependently.
Dissertation or thesis originally submitted to ProQuest.
He, Deling, "Acoustic-driven and cross-language effects on neuro-behavioral synchronization to speech rhythms" (2023). Electronic Theses and Dissertations. 3294.