Donath, Th., Natke, U., & Kalveram, K.Th. (2002) Effects of frequency-shifted auditory feedback on voice F0 contours in syllables. Journal of the Acoustical Society of America, 111(1), 357-366.

Abstract
Previous studies have shown that, during continuous vocalization, voice fundamental frequency (voice F0) is modified by frequency shifted auditory feedback. In this study, voice F0 contours were determined for the first two syllables of a non-sense word. This way effects of auditory frequency shift and a social stressor (public speaking) on voice F0 were investigated. Results showed that voice F0 is auditorily controlled with a high latency and on supra-segmental level in speech. Public speaking did not have an effect on voice F0 control, which is attributed to its failure to induce stress when speaking a non-sense word repeatedly.