Advancing Our Understanding of Speech Motor Control Through an Investigation of Intermuscular Coherence in Typical Speakers

Abstract

There is a need to characterize intermuscular coherence (IMC) in selected muscles of the speech mechanism in order to establish its utility as a tool to study speech motor control. IMC is a correlation in the frequency domain that provides information about whether two signals (i.e., electromyographic (EMG)) are firing at the same frequency. Two muscles firing across the same frequency spectrum are thought to be receiving the same neural signaling or common neural drive. IMC measurements remain a largely unused method for studying speech motor control. However, initial studies using IMC to describe muscle activity in muscles of the speech mechanism suggest that this measurement may be sensitive to certain non-speech and speech requirements. Questions remain about IMC sensitivity to various speaking demands across the lifespan. In the first two studies, I compared the effects of lung volume, laryngeal demands, articulatory complexity, and cognitive linguistic demands on IMC in the respiratory (Study 1) and articulatory (Study 2) subsystems. Studies involved secondary analysis of surface electromyography (EMG) recordings from the intercostals, obliques, and orbicularis oris in healthy younger and older adults to determine the presence of task- or age-related differences in IMC. These data also included acoustic and respiratory kinematic recordings to provide context for IMC findings. In Study 3, intercostal and oblique IMC measurements on four tasks were compared across children, adolescents, younger adults, and older adults to investigate whether established developmental patterns of respiratory kinematics would be accompanied by age-related differences in IMC. This work adds to a growing body of literature supporting the utility of IMC in the study of speech motor control. In all three studies, the results revealed several differences in IMC values across the lifespan as well as key task-related differences within the respiratory and articulatory subsystems. The dissertation concludes with a summary of these findings, as well as a discussion of the limitations and future research directions.