Modeling the role of nonhuman vocal membranes in phonation

Although the mammalian larynx exhibits little structural variation compared to sound-producing organs in other taxa (birds-or insects), there are some morphological features which could lead to significant differences in acou stic functioning, such as air sacs and Vocal membranes. The vocal membrane (or "vocal lip'') is a thin upward extension of the vocal fold that is pres ent in many bat and primate species. The vocal membrane was modeled as an a dditional geometrical element in a two-mass model of the larynx. It was fou nd that vocal membranes of an optimal angle and length can substantially lo wer the subglottal pressure at which phonation is supported, thus increasin g vocal efficiency, and that this effect is most pronounced at high frequen cies. The implications of this finding are discussed for animals such as ba ts and primates which are able to produce loud, high-pitched calls. Modelin g efforts such as this provide guidance for future empirical investigations of vocal membrane structure and function, can provide insight into the mec hanisms of animal communication, and could potentially lead to better under standing of human clinical disorders such as sulcus vocalis. (C) 1999 Acous tical Society of America. [S0001-4966(99)03602-4].