Phase-locked responses to speech in human auditory cortex are enhanced during comprehension

Area of Science:

• Neuroscience
• Auditory Perception
• Speech Processing

Background:

• Auditory cortex oscillations phase-lock to acoustic rhythms, enhancing environmental cue detection.
• The role of linguistic content in modulating neural entrainment to speech is not fully understood.

Purpose of the Study:

• To investigate whether linguistic information enhances neural phase-locking to intelligible speech.
• To determine the neural correlates and lateralization of this enhanced entrainment.

Main Methods:

• Magnetoencephalography (MEG) recorded neural activity in 16 adults listening to sentences.
• Speech intelligibility was manipulated using noise-vocoding while preserving acoustic envelopes.
• Neural activity phase-locking to speech envelopes was analyzed in the 4-7 Hz frequency band.

Main Results:

• Neural phase-locking to speech acoustic envelopes occurred bilaterally, strongest in the 4-7 Hz range.
• Phase-locking was significantly enhanced for intelligible speech compared to unintelligible speech.
• This enhancement was left-lateralized and localized to the left temporal cortex.

Conclusions:

• Speech entrainment is influenced by both acoustic properties and the listener's ability to extract linguistic meaning.
• Linguistic information enhances neural processing of speech rhythm, suggesting a predictive coding framework for speech comprehension.
• Left temporal cortex plays a crucial role in integrating acoustic and linguistic cues for speech understanding.