Evaluating Neural Tracking of Rhythmic Information in Speech: Some Caveats and Challenges

The temporal structure of speech provides crucial information to listeners for comprehension: In particular, the slow modulations in the amplitude envelope constitute important landmarks to discretize the continuous signal into linguistic units. Contemporary models of speech perception attribute a major functional role to brain rhythmic activity in this process: By aligning their phase to the quasi-periodic patterns in speech, neural oscillations would facilitate speech decoding. We here review evidence from EEG/MEG studies showing neural theta-range (~4–8 Hz) tracking of syllabic rhythm, with a special interest in speech rate variations. We also discuss to what extent neural oscillatory coupling contributes to, and is in turn modulated by, speech intelligibility, namely whether it is only acoustically or also linguistically guided. We finally review some findings showing that in addition to auditory cortex, motor regions play an active role in the oscillatory dynamic underlying speech processing.