Applying nonlinear dynamics to the voice: a historical perspective

The recognition that nonlinear phenomena, including subharmonics, bifurcations and deterministic chaos, are present in human and animal vocalizations is a relatively recent one. I give a brief history of this revolution in our understanding of the voice, based on interviews with some of the key players and personal experience. Most of the key concepts and mathematical principles of nonlinear dynamics were already well worked out in the early 1980s. In the early 1990s, physicist Hanspeter Herzel and colleagues in Berlin recognized that these principles are applicable to the human voice, initially to baby cries. The physics and physiology underlying many of these nonlinear phenomena had remained mysterious up until then. This insight was later generalized to animal vocalizations. Nonlinear phenomena play a relatively peripheral role in most human vocal communication but are a common feature of many animal vocalizations. The broad recognition of the existence of nonlinear vocalizations, and the quantitative study of their production and perception, has now fuelled important and exciting advances in our understanding of animal communication. I concentrate on how the core concepts came into focus, and on their initial application to an ever-wider circle of call types and species, and end with a brief prospectus for the future.This article is part of the theme issue 'Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions'.