The Phonetic Potential of Nonhuman Vocal Tracts: Comparative Cineradiographic Observations of Vocalizing Animals

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Abstract
For more than a century it has been noted that the adult human vocal tract differs from that of other mammals, in that the resting position of the larynx is much lower in humans. While animals habitually breathe with the larynx inserted into the nasal cavity, adult humans are unable to do this. This anatomical difference has been cited as an important factor limiting the vocal potential of nonhuman animals, because the low larynx of humans allows a wider range of vocal tract shapes and thus formant patterns than is available to other species. However, it is not clear that the static anatomy of dead animals provides an accurate guide to the phonetic potential of the living animal's vocal tract. Here I present X-ray video observations of four mammal species (dogs Canis familiaris, goats Capra hircus, pigs Sus scrofa and cotton-top tamarins Sagunius oedipus). In all four species, the larynx was lowered from the nasopharynx, and the velum was closed, during loud calls. In dogs this temporary lowering was particularly pronounced. Although preliminary, these results suggest that the nonhuman vocal tract is more flexible than previously supposed, and that static postmortem anatomy provides an incomplete guide to the phonetic potential of nonhuman animals. The implications of these findings for theories of speech evolution are discussed.