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201305 https://hdl.handle.net/2286/R.2.N.201305 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2025 2027-05-01T17:46:28 93 pages Doctoral Dissertation Academic theses en Ambadi, Pranav Satheesh Daliri, Ayoub Berisha, Visar Liss, Julie Arizona State University Partial requirement for: Ph.D., Arizona State University, 2025 Field of study: Speech and Hearing Science Cortical excitability suppression and beta-band event related desynchronization are hallmarks of healthy motor planning and display atypical patterns in movement and speech disorders as well. In speech planning, however, the roles of these neural measures are largely unknown. This dissertation addresses this knowledge gap using electroencephalography (EEG) and transcranial magnetic stimulation (TMS). The first two studies aimed to determine the time course of speech planning. TMS and EEG were used independently with delayed response tasks, where participants were randomly presented with condition and word stimulus cues, indicating whether they should speak or silently read a word at the upcoming go signal. These studies showed that cortical excitability increased significantly after the go signal in the speaking condition. Continuous beta trajectories indicated similar patterns for both speaking and silent reading conditions after the fixation and stimulus cues, suggesting that the alternating condition structure within blocks may have led participants to prepare similar motor speech plans for both conditions. The third and fourth studies aimed to manipulate feedforward processing in the speech planning phase and examine the effects on the two neural measures and early speech variability. Two condition types, syllable length of speech output and Delayed Auditory Feedback (DAF), were used in a delayed response paradigm, ensuring that all trials within a block pertained to only one condition combination. Syllable length, but not DAF, significantly modulated participants’ cortical excitability, beta desynchronization, and speech variability. A strong positive correlation was found between beta desynchronization and speech variability when planning multisyllabic words under normal auditory feedback. These findings suggest that beta desynchronization and cortical excitability are linked to feedforward processing in motor speech planning. Neurosciences cortical activity EEG Speech Planning Speech Production speech variability TMS Functional Significance of Pre-Speech Motor Cortical Activity