Jian Wenjuan, Chen Minyou, McFarland Dennis J
State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing, China.
State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing, China.
Brain Res Bull. 2017 Apr;130:156-164. doi: 10.1016/j.brainresbull.2017.01.023. Epub 2017 Feb 1.
Phase-locking value (PLV) is a well-known feature in sensorimotor rhythm (SMR) based BCI. Zero-phase PLV has not been explored because it is generally regarded as the result of volume conduction. Because spatial filters are often used to enhance the amplitude (square root of band power (BP)) feature and attenuate volume conduction, they are frequently applied as pre-processing methods when computing PLV. However, the effects of spatial filtering on PLV are ambiguous. Therefore, this article aims to explore whether zero-phase PLV is meaningful and how this is influenced by spatial filtering. Based on archival EEG data of left and right hand movement tasks for 32 subjects, we compared BP and PLV feature using data with and without pre-processing by a large Laplacian. Results showed that using ear-referenced data, zero-phase PLV provided unique information independent of BP for task prediction which was not explained by volume conduction and was significantly decreased when a large Laplacian was applied. In other words, the large Laplacian eliminated the useful information in zero-phase PLV for task prediction suggesting that it contains effects of both amplitude and phase. Therefore, zero-phase PLV may have functional significance beyond volume conduction. The interpretation of spatial filtering may be complicated by effects of phase.
锁相值（PLV）是基于感觉运动节律（SMR）的脑机接口中一个广为人知的特征。零相位PLV尚未得到研究，因为它通常被视为容积传导的结果。由于空间滤波器常用于增强幅度（带功率（BP）的平方根）特征并减弱容积传导，所以在计算PLV时，它们经常被用作预处理方法。然而，空间滤波对PLV的影响尚不明确。因此，本文旨在探讨零相位PLV是否有意义以及它如何受到空间滤波的影响。基于32名受试者左右手部运动任务的存档脑电图数据，我们比较了使用大拉普拉斯算子进行预处理和未进行预处理的数据的BP和PLV特征。结果表明，使用耳部参考数据时，零相位PLV为任务预测提供了独立于BP的独特信息，这无法用容积传导来解释，并且在应用大拉普拉斯算子时显著降低。换句话说，大拉普拉斯算子消除了零相位PLV中用于任务预测的有用信息，这表明它包含幅度和相位的影响。因此，零相位PLV可能具有超出容积传导的功能意义。空间滤波的解释可能会因相位的影响而变得复杂。
