In what sounds like a twisted birthday party gone horribly wrong, Japanese researchers have shown that helium-huffing gibbons utilize the same vocal techniques as professional soprano singers. The study reveals that gibbons, whose vocalizations are unique among non-human primates, share a physiological similarity to humans.
The unique project was led by Takeshi Nishimura from the Primate Research Institute at Kyoto University, Japan. The study, which was published in the American Journal of Physical Anthropology, analyzed the singing of white-handed gibbons at Fukuchiyama City Zoo, in northern Kyoto.
Gibbons have a very distinctive call as far as primates go — a song that features a loud melody that can be heard for miles. The apes use these vocalizations to communicate with neighboring pairs, strangers, and potential mates through what is often dense jungle where visibility is poor.
The human vocal tract is similarly distinctive and complex. It's this unique physiology that allows us to make variable, soft sounds through the rapid movement of our vocal tracts. Consequently, scientists have suspected that human speech is special, that it evolved through different evolutionary channels, and via specific modifications in our vocal anatomy.
Nishimura's study, however, shows that this theory may not be correct — and that humans share certain vocal qualities with gibbons. But how was Nishimura and his team able to show this by having gibbons breathe helium?
Well, as every six-year old knows, helium gas make human voices sound higher pitched. It does this by shifting the resonance frequencies of the vocal tract upwards. Helium is useful in studying animal vocal mechanisms, therefore, because it increases sound velocity and resonance frequencies.
During the experiment, the researchers recorded 20 gibbon calls in normal air atmosphere. Then they recorded nearly 40 calls in a helium-enriched environment. Analysis of the recordings showed that gibbons were consciously manipulating their vocal cords and tract when singing. Recordings of the helium-breathing gibbons can be found here.
Speaking through a release, Nishimura noted that:
The lowest frequency of harmonics is amplified in a gibbon's song when performed in normal air. However, in a helium-enriched atmosphere the tuning of the vocal cord vibration and the resonance of the vocal tract are altered as the gas causes an upward shift of the resonance frequencies.
Consequently, the study reveals that, like humans, gibbons share an independence between the origin of the sound and the vocal tools used to manipulate it. In other words, gibbons use the same process for producing speech like humans — where sound starts at the larynx and is controlled by a filter (namely, the shape of the supralaryngeal vocal tract). Scientists call this the "source-filter" process of speech production.
And interestingly, the discovery shows that gibbon vocalizations are always in soprano mode. This is difficult for humans, and is only mastered by professional opera singers. But what this also shows is that the human voice is tremendously versatile — and that we share the same biological fundamentals of vocalization with other primates. The entire study can be found here.