Tracking larynx movement in real-time MRI data

Ejective and implosive consonants involve rapid raising or lowering, respectively, of the larynx coordinated with an oral constriction formation and release. Techniques such as contour tracking and region-of-interest (ROI) direct image analysis are becoming established for examining supralaryngeal constriction formation in real-time MRI data, but quantification of larynx movement from dynamic vocal-tract magnetic resonance imaging has not been tackled. We will evaluate methods of indexing the movement of the larynx in fast real-time MRI data collected in the midsagittal plane. We analyze data from USC’s real-time MRI IPA database produced by several phoneticians and data from speakers of the Hausa language producing both ejectives and implosives. Kinematic profiles of the laryngeal movements are obtained by outlining the arytenoid structure and applying principal component analysis on the vocal-tract outlines. In addition, vertical movement of the larynx is indexed by calculating the time-varying pixel intensity centroid (i.e., intensity-weighted average spatial position) in a rectangular ROI defined for larynx movement. Once direct measurement of the larynx actions is validated for this type of imaging data, further work will focus on the temporal coordination of the laryngeal raising/lowering gestures and the supralaryngeal constriction gestures that occur in glottalic airstream consonants. [Work supported by NIH.]