Use of phase-locking value in sensorimotor rhythm-based brain-computer interface: zero-phase coupling and effects of...

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Phase-locking value (PLV) is a key feature for sensorimotor rhythm-based brain-computer interfaces (BCI).
• Concerns exist regarding spurious zero-phase coupling due to volume conduction and the independence of PLV from spectral amplitude.
• The effect of spatial filtering on reducing volume conduction and its impact on PLV remain unclear.

Purpose of the Study:

• To investigate the meaningfulness of zero-phase PLV in EEG signals.
• To determine how spatial filtering techniques affect PLV.
• To explore the relationship between PLV, spectral amplitude, and volume conduction.

Main Methods:

• Extracted amplitude and PLV features in the 10-15 Hz band from archival EEG data of 18 subjects.
• Utilized classical signal processing methods for feature extraction.
• Analyzed right ear-referenced data and data processed with a large Laplacian spatial filter.

Main Results:

• Identified meaningful long-range zero-phase synchronization in right ear-referenced data, likely involving motor and supplementary motor areas, not attributable to volume conduction.
• Observed that the Laplacian spatial filter enhanced amplitude but diminished phase information.
• Demonstrated that bipolar channels in phase-coupled areas retain both phase and amplitude information.

Conclusions:

• Zero-phase PLV provides meaningful information in BCI applications, independent of volume conduction.
• Spatial filtering techniques like the Laplacian filter can alter phase information, impacting PLV.
• Bipolar channels in phase-coupled regions offer a practical BCI approach, integrating both phase and amplitude features with reduced channel requirements.