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Speech and Nonspeech Production in the Absence of the Vocal Tract

  • Author(s): Thompson, Megan
  • Advisor(s): Nagarajan, Srikantan
  • et al.

Sensory feedback plays a crucial role in speech production in both healthy individuals and in individuals with production-limited speech. However, the vast majority of research on the sensory consequences of speech production has focused on auditory feedback while relatively little is known about the role of vocal tract somatosensory feedback. The body of this dissertation investigates speech and nonspeech production in the absence of vocal tract somatosensory feedback by training subjects to use a touchscreen-based speech production platform. Contact with the touchscreen results in instant playback of a vowel or complex tone dependent on the location selected. Because the axes of the touchscreen are associated with continuous F2 and F1 frequencies, every possible vowel within a wide formant range can be produced. Participants with no initial knowledge of the mapping of screen areas to playback sounds were asked to reproduce auditory vowel or complex tonal targets. Their responses were evaluated for accuracy and consistency, and in some cases participants underwent functional neuroimaging via MEG during training. Following training, participants were capable of using the touchscreen to produce speech and nonspeech sounds in the absence of the vocal tract. Their increased accuracy and consistency as they learned to produce speech and nonspeech sounds indicates the development of new audiomotor maps, as does significant changes in their task-based functional neuroimaging over the course of training. While participants demonstrated learning in both speech and nonspeech production, the neural and behavioral differences indicated different learning processes. We hypothesize that these differences can at least partially be attributed to the presence of an existing audiomotor network for producing speech sounds. This would account for more rapid learning rates in the speech variants of the task, the presence of generalization in touchscreen-based speech production, and the neural similarities to vocal speech production in the touchscreen-produced speech sounds that presented differently in touchscreen-produced nonspeech sounds.

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