These features together shape vowel sounds in humans. Here, we combine human phonetic and animal acoustic approaches including lip, tongue and jaw articulation movements and formant assessment, where formants are the broad spectral peaks that result from acoustic resonances in the vocal tract. Recent studies suggest that using human phonetic concepts that characterize vowel sounds, including formant analyses, can also be informative in describing vocal modulation in non-human primates. Hampering comparative research is the continued lack of a common methodology for assessing human and non-human vocal production. Given that speech and language do not fossilize, comparative research with other species can provide fruitful insights, and of particular relevance, pinpointing areas of consistency and divergence across the vocal repertoires of our closest living relatives, the non-human primates. Here, we address the emergence of vowel sounds universal to human speech production. The origins of human speech are obscure, and the order of emergence of components required for speech to evolve is much debated. This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part II)’.
Studies on more primate species will be required to substantiate this. Unlike recent studies suggesting monkeys achieve human vowel space, we conclude from our results that supra-laryngeal articulatory capacities show moderate evolutionary change, with vowel space expansion continuing through hominoid evolution. Comparing our results with published primate data, humans show less F1–F2 correlation and further expansion of the vowel space, particularly for sounds. Formant maps distinguished call types with different vowel-like sounds. Chimpanzee lip and jaw articulation variables also offered similar discrimination of call types. Discriminating acoustic features include voice quality and formant structure, mirroring phonetic features in human speech. Both discriminant and principal component classification procedures revealed classification of call types.
Data were collected from wild adult chimpanzees, Taï National Park, Ivory Coast. We examined visible supra-laryngeal articulators of four major chimpanzee vocalizations (hoos, grunts, barks, screams) and their associated acoustic structures, using techniques from human phonetic and animal communication analysis. We asked what chimpanzee and human vocal production acoustics have in common.
The origins of human speech are obscure it is still unclear what aspects are unique to our species or shared with our evolutionary cousins, in part due to a lack of a common framework for comparison.
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