The entrainment of EEG delta oscillations in speech listening

Abstract

Research on the sensory entrainment of neural oscillations provides a novel way of understanding how the brain processes spoken language without postulates of interim linguistic units. Several reports have shown that oscillations in the theta range (3-10 Hz) are entrained by syllable-size modulations in the energy envelope of speech. This entrainment has recently been shown to provide sensory frames in processing feature-related cues. A similar perspective has been applied to delta waves (< 3 Hz). Thus, it is suggested that delta entrains to long (“sentence”-size) energy contours, and this would provide processing frames involved in utterance comprehension. The present paper adopts a different viewpoint based on our previous work showing that delta-size perceptual chunks in speech relate to an online sensory memory of sequential information. We used electro-encephalography (EEG) to monitor listeners (n=18) on-line responses to utterance stimuli with controlled patterns of energy, pitch, and temporal marks. Measures of inter-trial phase coherence in neural oscillations show that delta specifically entrains to temporal chunks in the stimuli. This supports a view that delta is not entrained by sentence-size patterns but by perceptual chunks which provide sensory frames in processing incoming sequential information in heard speech.