Dissociating prosodic from syntactic delta activity during natural speech comprehension

Area of Science:

• Neuroscience
• Cognitive Science
• Linguistics

Background:

• Human speech perception involves segmenting acoustic signals into linguistic units for understanding.
• Prosodic cues like pauses aid speech segmentation, but their interaction with higher-level linguistic processing remains unclear.

Purpose of the Study:

• To investigate the neural mechanisms underlying speech segmentation by dissociating the processing of prosodic pauses from multi-word chunk segmentation.
• To determine the role of low-frequency brain activity in integrating acoustic and linguistic information during speech perception.

Main Methods:

• Magnetoencephalography (MEG) was used to record brain activity.
• Neural tracking of prosodic pauses and multi-word chunks was analyzed.
• Speech-brain coherence at different frequency bands was examined in response to manipulated pause regularity.

Main Results:

• Disrupting pause regularity affected slow (below 2 Hz) speech-brain tracking in auditory areas and increased higher-frequency (25-45 Hz) activity at speech onsets.
• Multi-word chunks were processed via low-frequency (below 2 Hz) rhythmic fluctuations, independent of prosodic cues.
• Low-frequency alignment at chunk onsets improved encoding model accuracy in auditory and frontal areas.

Conclusions:

• Low-frequency delta activity independently supports the processing of acoustic prosody and abstract linguistic units (multi-word chunks).
• This finding offers new insights into the neural basis of speech perception and compositional meaning.
• Speech-brain synchronization in the delta frequency range is critical for both segmentation and understanding complex linguistic structures.