Methodological Considerations and Findings of a Vowel Perturbation Study in Typically Developing Children

Background: Auditory feedback enables the speech production system to compensatively correct for articulatory errors and to adaptively calibrate feedforward commands. Less is known about how these feedback control processes develop. Development can be probed by comparing how younger and older children compensate and adapt for experimentally-perturbed vowels in their auditory feedback. Aims: The aims of this work were to evaluate methods for real-time vowel estimation and tracking; to devise appropriate methods for meaningful analysis of data; and to apply those methods in a vowel perturbation study with children aged 4 to 9 years old, towards furthering an understanding of developmental speech motor control. Evaluation of vowel estimation and tracking: Audapter vowel perturbation software was tested on real and synthetic speech samples. The software was evaluated to be appropriate for use in children aged 4 to 9, within error margins of 60 Hz for F1 and 180 Hz for F2. Development of analyses: Circular statistical methods were demonstrated as a means to gain insight from directional vowel changes in F1-F2 space during compensation and adaptation; these methods supplement existing approaches to analyze changes in F1 and F2 separately. Vowel perturbation study: Children compensated and adapted for vowel perturbation, but younger and older children accomplished this in different ways. While older children compensated more directly to oppose the perturbation, younger children altered their vowels less directly, indicating that the role of auditory feedback within the speech system changes during development. Adaptation to perturbation was more variable than compensation in both groups. Contributions: This work contributes performance metrics for Audapter research software in children. The application of descriptive circular statistics to analyze vowel perturbation data was demonstrated. Preliminary evidence indicates that there are developmental differences in the manner in which children respond to vowel perturbation. There may be developmental differences in the manner in which sensory information is integrated (i.e. auditory with somatosensory) that could underlie these findings. Future research, using the circular analytical methods described in this dissertation, is needed to investigate this possibility, and to generate additional evidence towards furthering the understanding of auditory feedback integration in developing speech motor control.Ph.D