8 - Relating Neural Oscillations to Syllable Cycles and Chunks

Summary

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.