A critical review of models of speech-motor control serves to illustrate the ongoing problem of elaborating an interface between speech and concepts of phonemes or “syllables” as groups of phonemes.The problem extends to neuro- and psycho-linguistic models. In addressing the issue of“the interface that never was,” several lines of evidence are presented that demonstrate syllable-size cycles as basic sequencing units of articulation, muscle activation, and representation in sequence memory. The evidence also suggests that a conceptualization of speech in terms of linguistic-type+/– features that are taken to be timed in letter-like bundles have oriented models, but fundamentally misrepresent both the timing and the graded control of muscles and articulatory motions. Instrumental records of graded control support coherent syllable-size cycles as basic sequencing units and evidence is discussed with a view on how syllable-internal timing can relate to intrinsic properties of relaxing tissues which do not imply a sequential control of closing and opening motions within a motion cycle.

The entrainment of neural oscillations to attributes of signals provides a key principle by which one can evaluate how the brain interfaces with structures of motor speech. For many authors, frequency-specific entrainment of delta (< 3 Hz) and theta (4–10 Hz ) oscillations to groups and syllable-size energy modulations define processing frames. However, there is little agreement on the type of information that is processed in the frames. A review is provided of diverging views on the role of entrainment and controversial claims that oscillations entrain to non-sensory units like words and phrases. A critical experiment is presented showing that, whereas theta oscillations entrain to acoustic attributes even in sequences of tones, delta entrains specifically to signature marks of chunking in speech stimuli regardless of whether the stimuli are meaningful utterances or meaningless series of syllables. By this evidence, delta waves do not entrain primarily to putative syntactic units but more generally to chunks of articulated sounds, which is consistent with a body of evidence demonstrating that chunking is a domain-general principle involved in processing motor sequences.