Abstract:

The evolutionary process of the source-filter theory has been challenged by little knowledge of voice physiology in non-human primates. Varied call repertoire of many species of non-human primates has been described based on acoustic evidence. The physiological mechanisms of animal vocalization are often examined by the acoustics of ‘helium voices’. Our acoustic analyses of helium voices indicated that voices in non-human primates are usually produced by source–filter independence as seen in human speech. While little is known about the underlying laryngeal function, vocal fold vibration can be assessed with electroglottography (EGG) where a low intensity and high-frequency current is passed between two electrodes placed on each side of the larynx. This approach provides preliminary evidence supporting for that distinct laryngeal mechanisms (comparable to “registers” in human singing) might underlie different calls, e.g., coos and the grunts, in macaques. The evolutionary antiquity and universality of human speech physiology are emphasized in primates.