[en] This paper presents some preliminary results of a study that aims to describe the articulatory capacities of Bonobos from acoustic data. Most studies of vocalizations with chimpanzees and Bonobos (e.g. Marler 1969, de Waal 1988, Mitani et al. 1992, Bermejo and Omedes 1999) focused on the interpretation of the vocal behavior of both captive and free-ranging groups to relate sounds produced to their semantic contexts. Spectrographic analyses reveal the acoustic structure of the vocalizations but rarely raise the question of the specific capacities of Bonobos in relation to the acoustics. This point is essential if one wants to understand the articulatory control that Bonobos have on their vocalizations.
Articulatory data come from dissections and 3D scans made on dead specimens. These data allow an accurate description of the size and shape of the Bonobo's vocal tract. Our data come from 1 male, 1 female and 1 juvenile. From an articulatory viewpoint, the question is to establish the role played by the lips, the jaw, the velum, and the tongue during vocalizations. Two other parameters are considered : (i) the role of the larynx and the type of control made by Bonobos on their vocal folds ; (ii) the role of the respiratory system during the production of sounds.
Vocalizations have been obtained in captivity at Planckendael and a simultaneous recording of sound and video was made. Data have been organized to make a repertoire of the vocalizations produced during those recording sessions. The first results show that Bonobos seem to have an active control on their jaw opening and that they modulate sounds very actively with their lips. They also seem to modulate the vocal output on the temporal and spectral levels. From our data it seems that the respiratory system might play a more important role than expected in order to modulate the intensity of the vocalizations. Indeed what seems intriguing is the apparent active control of the intensity's modulations when they are compared to the few variations observed on pitch during vocalizations. For each of these observations acoustic cues are available and clearly identified on spectrographic data. The role played by the tongue during the vocalizations is of course important but the relation between tongue movements and the acoustic cues suggest that it is rather a passive role. The role played by the velum is not easy to understand because the acoustic features, characteristic of nasal sounds, are still difficult to understand from our data. On the one end it seems that the rather flat vocal tract shape (compared to humans) would favor a greater role for the nasal cavities during the production of sounds. But on the other end, the intensities reached during vocalizations do not correspond to anything known in the acoustics of the coupling between oral and nasal cavities. Finally, for each identified acoustic cue during a vocalization, a relation is made with an articulatory parameter and a short video movie displays the sounds in context.
