abstract: The activation of the primary motor cortex (M1) is common in speech perception tasks that involve difficult listening conditions. Although the challenge of recognizing and discriminating non-native speech sounds appears to be an instantiation of listening under difficult circumstances, it is still unknown if M1 recruitment is facilitatory of second language speech perception. The purpose of this study was to investigate the role of M1 associated with speech motor centers in processing acoustic inputs in the native (L1) and second language (L2), using repetitive Transcranial Magnetic Stimulation (rTMS) to selectively alter neural activity in M1. Thirty-six healthy English/Spanish bilingual subjects participated in the experiment. The performance on a listening word-to-picture matching task was measured before and after real- and sham-rTMS to the orbicularis oris (lip muscle) associated M1. Vowel Space Area (VSA) obtained from recordings of participants reading a passage in L2 before and after real-rTMS, was calculated to determine its utility as an rTMS aftereffect measure. There was high variability in the aftereffect of the rTMS protocol to the lip muscle among the participants. Approximately 50% of participants showed an inhibitory effect of rTMS, evidenced by smaller motor evoked potentials (MEPs) area, whereas the other 50% had a facilitatory effect, with larger MEPs. This suggests that rTMS has a complex influence on M1 excitability, and relying on grand-average results can obscure important individual differences in rTMS physiological and functional outcomes. Evidence of motor support to word recognition in the L2 was found. Participants showing an inhibitory aftereffect of rTMS on M1 produced slower and less accurate responses in the L2 task, whereas those showing a facilitatory aftereffect of rTMS on M1 produced more accurate responses in L2. In contrast, no effect of rTMS was found on the L1, where accuracy and speed were very similar after sham- and real-rTMS. The L2 VSA measure was indicative of the aftereffect of rTMS to M1 associated with speech production, supporting its utility as an rTMS aftereffect measure. This result revealed an interesting and novel relation between cerebral motor cortex activation and speech measures. / Dissertation/Thesis / Doctoral Dissertation Speech and Hearing Science 2018

The purpose of this study was to compare changes in acoustic and kinematic measures of articulation across soft, comfortable, and loud speech conditions. There were 19 participants, 9 male and 10 female, with age ranging from 20 to 34 with a median age of 25. Each participant had electromagnetic sensors glued to their tongue, jaw, and lips. It was anticipated that the acoustic measures would accurately reflect the kinematic measures of speech as articulation changed across the intensity levels. Vowel space area (VSA) and vowel articulation index (VAI) were computed from the three corner vowels, /α, i, u/. Articulatory-acoustic vowel space (AAVS), a sentence-level acoustic measure, was computed from the continuous formant histories for all voiced segments in a sentence. Kinematic-vowel space area (KVSA), kinematic-vowel articulation index (KVAI), and articulatory-kinematic vowel space (AKVS) were the kinematic equivalents of the acoustic measures, and were newly developed for the present study. Stroke metrics based on the speed history of the lingual movements were also used to reveal average kinematic features of the articulatory gestures in each participant's speech. The data revealed that the isolated acoustic and kinematic measures that used corner vowels (VSA, VAI. KVSA, KVAI) did not change significantly with intensity. The sentence-level continuous measures of articulatory working space (AAVS and AKVS) increased as speech intensity increased. The other sentence-level kinematic metrics also changed significantly with speech intensity, including increases in hull volume, onset speed, peak speed, mean speed, and distance. Stroke duration decreased as speech intensity increased. These findings suggest that measures based on isolated corner vowels are not as reflective as continuous measures of changes in articulatory movement in speech.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has received more attention in recent years as a treatment option for regulating the symptoms of Parkinson's disease. Previous studies of DBS documented consistent improvements in motor function but more variability in speech outcomes. In the present study, six participants diagnosed with idiopathic Parkinson's disease who reported worsened speech with stimulation were recorded performing speech acoustic tasks with the stimulators on, and again with the stimulators off. Improvements were noted for most participants in measurements of formant slopes, long term average spectrum (LTAS) of a sustained vowel, and spirantization with stimulation on. Stimulation negatively affected most participants' vowel space area, verbal fluency, sequential motion rate, and LTAS while reading and describing a picture. Measures of stop gap duration, alternating motion rate, and voice onset time were within normal limits for most participants across both stimulation conditions.