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Does cortical entrainment exist? What we can learn from studying perception of naturalistic speech
The popular theoretical framework of cortical entrainment postulates that speech comprehension crucially depends on the continuous alignment of low-frequency cortical oscillatory activity with the amplitude envelope of perceived acoustic speech signals. This alignment has been suggested to represent a neural sampling mechanism that packages the incoming speech into discrete chunks, which are then transmitted to higher-order cortical regions for subsequent processing and extraction of meaning from an utterance.
Empirical evidence for cortical entrainment mostly stems from tightly controlled experimental paradigms focusing on repeated perception of isolated sentences or of read-aloud texts. However, these kinds of stimuli do not reflect natural speech as we encounter it in real life: spontaneously produced, real-life speech demonstrates variable speaking rate, and is characterised by significant disfluencies in the forms of interruptions, repetitions, filler words and revisions.
In my talk, I advance the view that naturalistic experimental paradigms, utilising spontaneously produced speech as stimuli and suitable frequency-domain methodological tools, should be used to address an important question that remains open: whether cortical entrainment is observed during speech perception and comprehension in real-life communicative situations, as opposed to tightly controlled experimental settings.
I also present evidence that the phenomenon currently labelled as cortical entrainment might be confounded by a regular repetition of evoked responses, based on the analysis of the acoustic structure of isolated sentences, read-aloud texts and spontaneously produced speech.
Finally, I propose different alternative viewpoints of what spontaneously produced, real-life speech could teach us about cortical entrainment and language comprehension, in general.