MRI & CT Studies of the Developing Vocal Tract

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I. Project Summary/Abstract: The postnatal growth of the oral and pharyngeal structures and their respective cavities - that define the vocal tract (VT) - entails changes in size, shape, and relative proportions. While prenatal and postnatal growth comprise a developmental continuum, current theory strongly associates the postnatal functions of the VT structures to guide its growth, particularly during infancy and early childhood. Acoustic theory affirms a relationship between the anatomy of the developing VT and the spectrum of speech sounds observed during development. However, although the available anatomic information remains inadequate to explain this relationship in detail, our VT Development Lab has made steady progress since 2000 towards its mission to quantitatively characterize sex-specific anatomic changes of the supralaryngeal speech system during development by: i) Establishing a unique imaging database consisting of 1116 MRI and CT studies across the lifespan that is representative of both sexes. ii) Compiling a large set of measurements that capture the concurrent growth of the head, face and VT structures throughout the lifespan; and creating composite 3D models where the spatial relation between select VT structures is maintained and from which measurements on relational growth will be secured. iii) Characterizing systematically the individual and relational growth of VT structures (ex. Vorperian et al. 1999, 2005), and synthesizing findings on the acoustic output of the developing VT, specifically the development of vowel acoustic space (Vorperian & Kent, 2007). This proposed project combines imaging, acoustic analysis of speech, acoustic reflection or acoustic pharyngometry data, and VT modeling in an investigation on the development of the supra-laryngeal speech apparatus throughout the lifespan. The goals of this proposed research are to: (1) Expand the imaging and the measurements databases to include atypically developing cases, supplement measurements that are guided by embryologic origin of structures, and measurements from 3D models that capture additional information on the relational growth of VT structures. Also, to secure speech recordings and acoustic pharyngometry data mostly from individuals who will be imaged. (2) Assess perspectives on anatomic- acoustic relationships and structure/function interaction by statistically characterizing sex specific growth models and growth type of the VT structures in typically and atypically developing individuals; and assess their relative and relational growth while taking into account the structures' tissue type (bony, soft, cartilage and cavity), embryologic origin, plane of growth, and/or functional use. (3) Use complementary imaging and acoustic reflection data to configure developmental VT models and correlate model computed formant values with age specific acoustic data to make inferences regarding VT acoustic characteristics to developmental changes of specific anatomic structures. The findings will provide a coherent and much needed picture on the development of VT structures from embryo to geriatrics. Such information is foundational for both theoretical constructs and clinical application in multiple disciplines that deal with craniofacial structures and functions.