Speech considered as modulated voice

In addition to linguistically coded information, speech conveys necessarily also some paralinguistic information of expressive (affective and adaptive), organic and perspectival kind, but all respective features lack invariant absolute acoustic correlates. According to the Modulation Theory, a speaker’s voice functions as a carrier that is modulated by speech gestures. Listeners have to demodulate the signal. Speakers freely vary their voice but compensate for impediments to modulation. Listeners “tune in” to a speech signal based on intrinsic and extrinsic cues and evaluate the deviations of its properties from those they expect of a linguistically neutral vocalization with the same paralinguistic quality. It is shown how this is reflected in the results of various investigations. Most organic and some expressive information is conveyed in the properties of the carrier. Expressive factors affect also amplitude and rate of linguistic modulations. Acquisition and use of speech require a neural linkage between perceptual demodulation and speech motor control (echo neurons). The imitation of body postures and gestures requires analogous structures evidenced in mirror neurons. Relations with gestural theories of speech perception and models of production as well as implications for distinctive feature theory and for the representation of speech in memory are discussed.