Mammal Vocalisations and the Mechanisms Behind them

Before we enter the word of mammal sound and rhythm we need to understand the workings of how they make the sound and the rhythm. All of mammal vocalizations can be understood with the framework of nonlinear dynamics (Wilden, 1998). This nonlinear process is laryngeal sound production (Wilden, 1998).The driving force of a mammal’s vocalization is airflow which generally comes from the lungs and which is then relayed to the larynx via the bronchi and trachea (Wilden, 1998). When the vocal folds are set into vibrations by the combined effect of subglottal pressure this is known as a phonation (Wilden, 1998). In having a great variety of sounds there can also be complex interactions of aerodynamic and biomechanical forces can be induced (Wilden, 1998). Basically, the fold tissues and the vocal fold collisions create the essential nonlinear characteristics of the sound generating system (Wilden, 1998). To understand the complexities in nonlinear process, a brief look into the linear systems will help with the understanding.

In a linear process only damped oscillations are possible (Wilden, 1998). There is already a manifestation of nonlinear behaviour which is sustained by self-sustained vibrations of vocal folds (Wilden, 1998). The nonlinear system can generate complex outputs without any random external input into the vocal apparatus (Wilden, 1998). In contrast, a linear system, any irregularity must be assigned to random components (Wilden, 1998).

Now back to nonlinear systems and its dynamics. Within the dynamics of the nonlinear system there are two major components; Attractors and bifurcations. The attractor can be defined as the sound generation at constant parameters (Wilden, 1998).So the vibrations of the vocal folds are very fast with periods in order of milliseconds (Wilden, 1998).  The variation in the muscle tensions and lung pressures are much slower, therefore the parameters can be seen as constant during a steady sound generation (Wilden, 1998). The attractors are the corresponding geometric object in phase space (Wilden, 1998).  There are three attractor types; steady state, limit cycle and Torus (Wilden, 1998). The other component is Bifurcations.

The bifurcations are essentially the transitions due to varying parameters (Wilden, 1998). The bifurcations are also defined as the abrupt changes of attractors for varying parameters (Wilden, 1998). There are a couple of bifurcations which are most relevant to mammal vocalizations; Hopf bifurcation, Subharmonic Bifurcation and secondary Hopf Bifurcation (Wilden, 1998). These nonlinear dynamics are the basis that can be used to understand and interpret the phenomena in mammal vocalization (Wilden, 1998). With the basic understanding of the mechanics behind mammal vocalization we can now explore the world of sound in the mammal world.

Works Cited

Wilden, I., 1998. Subharmonics Biphonation, and Deterministics Chaos in Mammal Vocalisation. Bioacoustics: the international journal of Animal sound and its recording , 9(3), pp. 171-196.