Acoustic observables of sound source-tract coupling

EZEQUIEL M. ARNEODO; YONATAN SANZ PERL; GABRIEL B. MINDLIN

Huerta Grande, Córdoba.

Congreso; SAN 2011 (Reunión anual de la Sociedad Argentina de Neurociencias); 2011

Sociedad Argentina de Neurociencias

Birdsong has become a favorite animal model to study complex, learned motor behavior. The observed behavior, the complex set of vocalizations, results of the interaction between a pattern generator in the central nervous system and a nonlinear biomechanical device: the vocal organ. We focus on complexity of the behavior introduced by the dynamics of the vocal organ, which is capable of producing a variety of complex vocalizations even when driven by simple motor gestures. In the vocal organ, a sound source is attached to a vocal tract. If the tract does not act as a mere filter, but is acoustically coupled to the source, nonlinear phenomena are introduced, which can leave a signature in the acoustical features of vocalizations. Inspired by the sound production mechanisms of songbirds, we study a mathematical model of a vocal organ, in which a simple sound source interacts with a tract. We explore the system numerically, and by taking it to the weakly nonlinear limit, we examine its periodic solutions analytically. Nonlinear features of the solutions are proposed as the underlying mechanisms of observed phenomena in birdsong, such as ``frequency jumps'', enhancement of resonances, and the shift of the fundamental frequency observed in heliox experiments.