Speech is a highly skilled motor activity that shares a core problem with other motor skills: how to reduce the massive degrees of freedom (DOF) to the extent that the central nervous control and learning of complex motor movements become possible. It is hypothesized in this paper that a key solution to the DOF problem is to eliminate most of the temporal degrees of freedom by synchronizing concurrent movements, and that this is done in speech through the syllable—a mechanism that synchronizes consonantal, vocalic and laryngeal gestures. Under this hypothesis, gestures are articulatory movements toward underlying targets; the onsets and offsets of the gestures are synchronized at the syllable edges, although more so at syllable onset than at the offset; and the realization of the synchronization is facilitated by sensorimotor feedback, especially tactile feedback, during consonant closures. This synchronization theory of the syllable also offers a comprehensive account of coarticulation, as it explicates how various coarticulation-related phenomena, including coarticulation resistance, locus, locus equation, diphone etc., are byproducts of syllable formation. It also provides a theoretical basis for understanding how suprasegmental events such as tone, intonation, phonation, etc. are aligned to segmental events in speech. It may also have implications for understanding vocal learning, speech disorders and motor control in general.
The acoustic counterpart to coarticulation resistance and aggressiveness in locus equation metrics and vowel dispersion