The prosodic governance of surface phonetic variation: Support for an alternative approach III

Effects of prosodic structure on surface phonetics are modeled in AP/TD in two ways: 1) via a set of PI and MuT adjustment mechanisms used to model lengthening effects at boundaries and on prominent syllables, and 2) via a hierarchy of coupled syllable, cross-word foot, and phrase oscillators, used to model poly-subconstituent shortening effects, and to control overall speech rate. These mechanisms are challenged by 1) findings presented in previous chapters that suggest that longer durations associated with boundaries and prominences are due to longer surface duration specifications, 2) findings presented here that show that polysyllabic shortening does not affect all words in an utterance, inconsistent with an oscillator-based mechanism that controls all aspects of any produced utterance, and 3) findings relating to speech rate presented in previous chapters which suggest that speech rate specifications relate to surface durations, rather than to planning oscillator frequencies. Patterns of speech timing presented in this chapter thus suggest that there are reasons to be uncertain whether periodicity is a major factor in speech motor control in typical speaking circumstances, and therefore call into question the use of suprasegmental oscillators.