Variation of maximal Lyapunov exponent with voice disorders of pilots

Abstract

The maximal Lyapunov exponent λ is a signature of chaos in the field of nonlinear dynamics. Analysis of vowels uttered by a troubled speaker can show irregularities and instabilities due to nonlinearities of the phonatory system. Therefore λ can be studied for the research of voice acoustic features able to present variations due to psychophysiological disturbances. These ones belong to the aeronautical context. Two pilots' voices have been recorded at stopovers during short-haul rotations on a day. A day of driving was used as an experimental material to study a similar workload. After being woken up in a laboratory sleep inertia experiment, another pilot is recorded. Finally, the Cockpit Voice Recorder of a crashed airplane provided a real-case corpus for the study. Vowels are extracted in all recordings and their maximal Lyapunov exponent is estimated. Regardless of whether or not the chaotic behavior of the voice, results show a large dispersion, little variations with different directions from the normal state of the speaker to the end of the recordings. On the basis of these experiments, the number of speakers involved, the choice of the calculation parameters, the phonetic material used, λ has a low sensitivity to the aeronautical psychophysiological disturbances. © 2013 Acoustical Society of America.