Lombard noted in 1911 that a speaker changes his voice level similarly when the ambient noise level increases, on the one hand, and when the level at which he hears his own voice (his sidetone) decreases, on the other. We can now state the form of these two functions, show that they are related to each other and to the equal-sensation function for imitating speech or noise loudness, and account for their form in terms of the underlying sensory scales and the hypothesis that the speaker tries to maintain a speech-to-noise ratio favorable for communication. Perturbations in the timing and spectrum of sidetone also lead the speaker to compensate for the apparent deterioration in his intelligibility. Such compensations reflect direct and indirect audience control of speech, rather than its autoregulation by sidetone. When not harassed by prying experimenters or an unfavorable acoustic environment, the speaker need no more listen to himself while speaking than he need speak to himself while listening.
Lane et al. (Wed,) studied this question.
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