Building on the progress in the current grant, the proposed research will address outstanding questions regarding glottal aerodynamics, focusing on (1) how inherently aerodynamic aperiodicity contributes to voice jitter and shimmer, (2) how airflow asymmetries arise and how they contribute to asymmetric vocal fold vibration, and (3) how aerodynamic energy losses in the glottal jet set the limits of voice efficiency for both symmetric and asymmetric vocal fold vibration. A combination of in vitro experiments and computer simulation will be used to study the evolution of glottal flow when model vocal folds (1) are moved in a prescribed manner, and (2) vibrate in response to aerodynamic forces. Both symmetrical and asymmetrical vocal fold motion will be studied. In the experimental studies, temporally and spatially resolved measurements of flow velocity and the vocal fold wall position will be performed using Digital Particle Image Velocimetry in a scaled-up model of the vocal folds. The computer simulations will utilize two approaches: first, a vortex-element model of the airflow; and second, a lumped-element model similar to those used in 2- mass models, but modified according to the findings from the experiments and vortex-element computations. For all cases studied, glottal volume flow jitter and shimmer will be characterized in terms of the glottal jet structure (vortex shedding, flow asymmetry). From both computer simulation and experimental data, the transfer of energy from the subglottal air stream to (1) vocal fold motion, (2) aerodynamic dissipation in the jet, and (3) acoustic energy will be estimated. This energy budget will be used to estimate voice efficiency and correlate it to (1) glottal volume flow jitter and shimmer and (2) asymmetry in both glottal flow and vocal fold motion. The experiments and model development will build on previous work of the investigators, combining expertise in experimental and computational fluid mechanics, aeroacoustics, flow-induced vibration, and the application of these to phonation. Participation of clinical voice researchers will also help give the proposed research clinical relevance. [unreadable] [unreadable] [unreadable]