Non-invasive documentation of primate voice production using electroglottography

Electroglottography (EGG) is a low-cost, non-invasive method for documenting laryngeal sound production during vocalization. The EGG signal represents relative vocal-fold contact area and thus delivers physiological evidence of vocal-fold vibration. While the method has received much attention in human voice research over the last five decades, it has seen very little application in other mammals. Here, we give a concise overview of mammalian vocal production principles. We explain how mammalian voice production physiology and the dynamics of vocal-fold vibration can be documented qualitatively and quantitatively with EGG, and we summarize and discuss key issues from research with humans. Finally, we review the limited number of studies applying EGG to non-human mammals, both in vivo and in vitro. The potential of EGG for non-invasive assessment of non-human primate vocalization is demonstrated with novel in vivo data of Cebus albifrons and Ateles chamek vocalization. These examples illustrate the great potential of EGG as a new minimally invasive tool in primate research, which can provide important insight into the ‘black box’ that is vocal production. A better understanding of vocal-fold vibration across a range of taxa can provide us with a deeper understanding of several important elements of speech evolution, such as the universality of vocal production mechanisms, the independence of source and filter, the evolution of vocal control, and the relevance of non-linear phenomena.