A three-dimensional model of the larynx and the laryngeal constrictor mechanism




Moisik, Scott

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This thesis documents the creation of a three-dimensional model of the larynx. The focus is on synthesizing the movement and appearance of laryngeal and pharyngeal sounds, with the intention of elucidating the physiological performance required of the larynx to produce these articulations. The model serves three primary purposes: the analysis of laryngeal articulation, an interactive tool for learning about linguistically relevant anatomy, and a foundation for future modeling developments such as acoustic synthesis. There are two methodological topics of discussion concerning the techniques used to generate the three-dimensional model of the larynx. The first concerns the morphological aspect of the laryngeal architecture. Laryngeal structures were segmented from a series of histological images using a process known as vertex tracing to generate wire-frame computer representations, or meshes, of the laryngeal structures featured in the model. The meshes were then carefully placed within the three-dimensional space used to generate a scene of the larynx that could be rendered and presented to the user of the program. Frame hierarchies, an organization scheme for vertices, were imposed on flexible tissue meshes to attach and manipulate various moving structures found in the larynx. Finally, basic mechanical features of laryngeal movement derived from research into the biomechanics of laryngeal physiology were implemented. The second methodological topic pertains to the analysis of laryngoscopic videos to obtain data that describes the movement patterns used to generate the laryngeal and pharyngeal articulations of interest. There are three image analysis techniques applied to the laryngoscopy. The first uses normal speed laryngoscopy to assess end-state articulations, by comparing various geometrical aspects of laryngeal landmarks as they differ between the maximally open setting (used for deep inspiration), and the articulatory target setting. With this technique, various phonation types and segmental articulations are assessed using videos of a phonetician carefully performing the articulations. Some comparison of these articulations to their analogues in the speech of native speakers from various languages is made for the sake of illustration and verification. The second image analysis technique used is applied to high-speed laryngoscopic video of aryepiglottic trilling, which is an important function of the laryngeal constrictor mechanism. The left and right aryepiglottic apertures during trilling are analyzed using binary-conversion and area measurement. The third technique takes the same high-speed laryngoscopic video of aryepiglottic trilling and extracts motion vectors between frame pairs to characterize the directionality and magnitude of motion occurring for each of the folds. Using the image analysis data, model movements are constrained and synchronized to recreate the articulations observed in the laryngoscopic videos. One of the major innovations of this model is a biomechanical simulation of aryepiglottic fold trilling, based primarily upon the data collected from the high-speed laryngoscopic videos. Overall the model represents one of the first attempts to visually recreate laryngeal articulatory function in a way that is dynamic and interactive. Future work will involve dynamic acoustic synthesis for laryngeal states represented by the model.



Articulatory Phonetics, Laryngeal Constriction, Aryepiglottic Folds, 3D Modeling