Dynamic Relations between Speaking and Hearing
Harlan L. Lane, Bernard Trane · The Journal of the Acoustical Society of America · 1969
People speak more loudly in a noisy room or when momentarily deafened and more softly in a quiet room or when sidetone is artificially increased. The effort to compensate for these changes in the signal-to-noise ratio, or to match directly changes in the intensity of a model, typically falls about half-way short (in decibel units). This is probably because a speaker considers that he has doubled his vocal level in half as many decibels as it takes for a listener to agree. More concisely, the Lombard-reflex, sidetone-penalty, and equal-sensation functions have slopes with absolute value ∼0.5 because the exponent of the autophonic scale of voice level is twice that of the loudness scale. This amounts to saying that the speaker acts so as to keep the signal-to-noise ratio, and hence his intelligibility, nearly constant; but he is misled by the differing sensory dynamics of speaking and listening. This disparity is important; none of the five functions supports the view that loudness is judged in terms of vocal level (Ladefoged), or the view that vocal level is judged in terms of loudness (Warren).