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Séminaire du département Parole et Cognition du 11/06/2015 à 13h30

 

Elephant on the bench - ex-vivo investigation of mammalian sound production

Intervenant : Christian Herbst, Voice Research Lab, Palacký University Olomouc / Laboratory of Bioacustis, University of Vienna

Lieu : B314

 

Résumé :

Excised larynx preparations allow studying the biophysics of mammalian sound production under controlled laboratory conditions. Research done in the past decades focused mainly on humans, but recently the approach has been extended to investigating nonhuman mammals. In this presentation, this author will present a partial overview of his own work with excised larynges, with relevance for the fields of bioacoustics and basic voice science. In particular, it will be shown that:

 

Elephants’ voice production mechanism for infrasound vocalizations below 20 Hz conforms to the myo-elastic aerodynamic theory of voice production (MEAD). This physical principle thus extends across a remarkably large range of fundamental frequencies and body sizes in mammals, spanning more than four orders of magnitude [1]. A method for visually and quantitatively assessing the regularity of vibrations of systems on the way to chaos is being presented [2]. This method is applied to categorizing vibratory states of two excised red deer larynges on the bench, suggesting that irregular vibration increases glottal efficiency by about 3 dB, possibly giving the animals an energetic advantage during acoustic signalling [3].

 

The remainder of the talk is concerned with a critical evaluation of electroglottography (EGG), a low-cost non-invasive impedance measurement method for monitoring some oscillatory aspects of vocal fold vibration. The EGG waveform’s purported correspondence to the time-varying vocal fold contact area was investigated in an excised hemi-larynx experiment involving two high-speed video HSV cameras operating at 6000 fps, synchronized with EGG, and the results suggest a tolerable but not perfect agreement [4]. Furthermore, an investigation of the coincidence of positive peaks in the derivative of the EGG waveform (dEGG) with incidents of glottal closure and opening, utilizing an excised larynx setup with synchronized ultra-HSV at 27000 fps was performed. Results show that dEGG peaks do not necessarily coincide with incidents of glottal closure and opening [5]. Findings from these last two studies suggest that EGG should be interpreted and analyzed with care, and that further research is necessary to establish expected error margins.

 

[1]        C. T. Herbst, A. S. Stoeger, R. Frey, J. Lohscheller, I. R. Titze, M. Gumpenberger, and W. T. Fitch, "How Low Can You Go? Physical Production Mechanism of Elephant Infrasonic Vocalizations," Science, vol. 337, pp. 595-599 2012.

[2]        C. T. Herbst, H. Herzel, J. G. Svec, M. T. Wyman, and W. T. Fitch, "Visualization of system dynamics using phasegrams," J R Soc Interface, vol. 10, pp. 1-14, 2013.

[3]        C. T. Herbst, "Glottal efficiency of periodic and irregular in vitro red deer voice production " Acta Acoustica united with Acoustica, vol. 100, pp. 724-733, 2014.

[4]        V. Hampala, M. Garcia, J. G. Svec, R. C. Scherer, and C. T. Herbst, "Relationship between the Electroglottographic Signal and Vocal Fold Contact Area," Journal of Voice, vol. submitted, 2015.

[5]        C. T. Herbst, J. Lohscheller, J. G. Svec, N. Henrich, G. Weissengruber, and W. T. Fitch, "Glottal opening and closing events investigated by electroglottography and super-high-speed video recordings," J Exp Biol, vol. 217, pp. 955-63, 2014.

 


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