Acoustically driven cortical delta oscillations underpin perceptual chunking

Oscillation-based models of speech perception postulate a cortical computational principle by which decoding is performed within a window structure derived by a segmentation process. In the syllable level segmentation is realized by a theta oscillator. We provide evidence for an analogous role of a delta oscillator at the phrasal level. We recorded MEG while participants performed a target identification task. Random-digit strings, with phrasal chunks of two digits, were presented at chunk rates inside or outside of the delta range. Strong periodicities were elicited by acoustic-driven chunk rates inside of delta, in superior and middle temporal areas and speech-motor integration areas. Periodicities were diminished or absent for chunk rates outside of the delta range, closely in line with behavioral performance. No periodicities were observed for top-down driven chunking conditions. Our findings show that phrasal chunking is correlated with acoustic-driven delta oscillations, expressing anatomically specific patterns of neuronal periodicities.