Hierarchy, Not Lexical Regularity, Modulates Low-Frequency Neural Synchrony During Language Comprehension

Area of Science:

• Neuroscience
• Psycholinguistics
• Computational Linguistics

Background:

• Neural responses synchronize with speech rhythm, particularly in the delta band (0.5-3 Hz).
• Debate exists whether this synchronization reflects hierarchical syntactic structure or simpler lexical/sequential regularities.
• Computational models suggest lexical information alone can explain observed synchronization patterns.

Purpose of the Study:

• To differentiate between hierarchical syntactic and lexical accounts of neural synchronization to speech.
• To investigate if delta-band synchronization specifically tracks syntactic structure.
• To provide empirical evidence for the role of syntax in auditory sentence processing.

Main Methods:

• Utilized electroencephalography (EEG) and a frequency-tagging paradigm with native Mandarin speakers (N=31).
• Developed a novel experimental condition with syntactically well-formed sentences versus sentences with reversed words within phrases.
• Employed computational simulations to model predictions of lexical and hierarchical accounts.

Main Results:

• Robust delta synchronization was observed for syntactically well-formed, isochronous speech.
• No significant delta synchronization pattern was found for speech with reversed words within phrases.
• EEG data supported the hierarchical account over the lexical account.

Conclusions:

• Neural delta synchronization to speech reflects hierarchical syntactic structure, not merely lexical content or word order.
• This finding provides crucial evidence for the brain's ability to track complex linguistic hierarchies during auditory processing.
• The study refines our understanding of the neural basis of sentence comprehension.