Modelling vocal anatomy's significant effect on speech

Abstract

This paper investigates the effect of larynx position on the articulatory abilities of a human-like vocal tract. Previous work has investigated models that were built to resemble the anatomy of existing species or fossil ancestors. This has led to conflicting conclusions about the relation between the evolution of anatomy and the evolution of speech. Here a model is proposed to systematically investigate the relation between larynx height and articulatory abilities. It is a simplified model of primate vocal anatomy that nevertheless preserves the essential articulatory constraints due to limitations of muscular control. It is found that there is an optimal larynx height at which the largest range of signals can be produced and that at this height, the vertical and horizontal parts are approximately equally long. This has been a conjecture for a long time by those researchers of the evolution of speech who propose that the human vocal tract has evolved for speech. A short recapitulation of acoustic theory of speech production is presented to explain the reason for why this configuration is optimal. The optimal configuration corresponds closely to human female anatomy, while in the human male the larynx is slightly lower than optimal. These results agree with the hypothesis that modern human vocal anatomy has evolved because of speech, and that male larynx position might have been lowered further for reasons of size exaggeration.