Ongoing slow oscillatory phase modulates speech intelligibility in cooperation with motor cortical activity

Area of Science:

• Neuroscience
• Cognitive Science
• Speech Processing

Background:

• Neural oscillations, particularly slow ones like delta and theta waves, are increasingly recognized for their role in speech recognition.
• Speech intelligibility is known to improve with the synchronization of speech rhythms and neural oscillations, observable via scalp electroencephalography (EEG).
• Beyond neural oscillations, speech recognition may also benefit from the processing of motor signals involved in speech production.

Purpose of the Study:

• To investigate the relationship between neural oscillations and motor cortical activity during speech recognition.
• To quantitatively assess the impact of EEG phase on behavioral performance in a speech recognition task.

Main Methods:

• Simultaneous scalp electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) were employed.
• Participants performed a speech recognition task involving spoken words presented amidst noise.
• A novel index was developed to quantify the influence of EEG phase on behavioral outcomes.

Main Results:

• The phase of delta and theta EEG oscillations preceding speech input significantly modulated response times during the speech recognition task.
• Simultaneous EEG-fMRI data revealed a correlation between slow EEG activity and activity within the motor cortex.
• A quantitative index effectively evaluated the EEG phase effect on performance.

Conclusions:

• The findings suggest that the phase of slow neural oscillations is linked to motor cortex engagement during speech recognition.
• This study provides evidence for the interplay between auditory processing (neural oscillations) and motor system activity in understanding speech.
• The results highlight the potential of using EEG and fMRI to understand the neural mechanisms underlying speech perception.