Stimulated production of vowel-like LX-waveforms and spectral damping in the absence of phonation

Electrical impedance ‘LX’ waveforms measured across the neck at the thyroid level during phonation are known to be correlated with vocal fold movement. Changes in vocal fold contact are thought to be the cause of this phenomenon though emerging applications in radiotherapy indicate that changes in the configuration of both fold and neck tissues are correlated with LX waveform shape. In this paper it is shown that a two-stage tissue damping model with controlled bandpass and passive low pass components is consistent with evidence from gradually degraded, controlled phonation. In particular it is shown that an externally applied stimulus to the vertebral processes of the neck can produce similar impedance waveforms in the absence of phonation and hence no controlled fold contact. It is postulated that this is initial evidence suggesting that both pressure waves and vocal fold contact components contribute to the production of the classical ‘LX’ waveform.