Structural and sequential regularities modulate phrase-rate neural tracking.

Area of Science:

• Neuroscience
• Psycholinguistics
• Cognitive Science

Background:

• Neural tracking synchronizes brain activity with speech rhythm, particularly grammatical phrases.
• Debate exists whether this tracking relies on syntactic structure or syntax-external factors like word sequences.
• Previous studies confounded syntactic and sequential information, limiting understanding.

Purpose of the Study:

• To investigate if the brain is sensitive to both syntactic properties and sequential word information during phrase-rate neural tracking.
• To differentiate the neural processing of grammatical structure versus sequential word repetitions in speech.

Main Methods:

• Used electroencephalography (EEG) to measure brain activity in 20 native Mandarin Chinese speakers.
• Participants listened to isochronous word streams containing grammatical phrases or non-grammatical word combinations.
• Varied syntactic factors (head position, attachment type) in grammatical sequences and part-of-speech repetition in non-grammatical sequences.
• Quantified neural tracking using evoked power and inter-trial phase coherence.

Main Results:

• Stronger neural tracking at the phrase rate was observed for grammatical sequences compared to non-grammatical ones.
• Phrase-rate tracking was modulated by attachment type and head position, indicating sensitivity to syntactic structure.
• The brain also tracked the repetition of parts of speech in non-grammatical sequences.

Conclusions:

• Neural tracking of speech rhythm is sensitive to syntactic structure, confirming its role in phrase processing.
• The brain also exhibits sensitivity to sequential regularities, such as repeated parts of speech, in non-grammatical contexts.
• These findings suggest an integrative view where the brain uses multi-level linguistic information for rhythmic processing in speech.