Sekihara K, Hild K E, Dalal S S, Nagarajan S S
Department of Systems Design and Engineering, TokyoMetropolitan University, Asahigaoka 6-6, Hino, Tokyo 191-0065, Japan.
IEEE Trans Biomed Eng. 2008 Mar;55(3):1112-21. doi: 10.1109/TBME.2008.915726.
This paper presents an analysis on the performance of the prewhitening beamformer when applied to magnetoencephalography (MEG) experiments involving dual (task and control) conditions. We first analyze the method's robustness to two types of violations of the prerequisites for the prewhitening method that may arise in real-life two-condition experiments. In one type of violation, some sources exist only in the control condition but not in the task condition. In the other type of violation, some signal sources exist both in the control and the task conditions, and that they change intensity between the two conditions. Our analysis shows that the prewhitening method is very robust to these nonideal conditions. In this paper, we also present a theoretical analysis showing that the prewhitening method is considerably insensitive to overestimation of the signal-subspace dimensionality. Therefore, the prewhitening beamformer does not require accurate estimation of the signal subspace dimension. Results of our theoretical analyses are validated in numerical experiments and in experiments using a real MEG data set obtained during self-paced hand movements.
本文对预白化波束形成器应用于涉及双重（任务和对照）条件的脑磁图（MEG）实验时的性能进行了分析。我们首先分析了该方法对于在实际双条件实验中可能出现的两类违反预白化方法前提条件情况的稳健性。在一类违反情况中，一些源仅存在于对照条件下，而不存在于任务条件下。在另一类违反情况中，一些信号源同时存在于对照和任务条件下，并且它们在两种条件之间强度发生变化。我们的分析表明，预白化方法对这些非理想条件非常稳健。在本文中，我们还进行了理论分析，表明预白化方法对信号子空间维度的高估相当不敏感。因此，预白化波束形成器不需要精确估计信号子空间维度。我们理论分析的结果在数值实验以及使用在自主节奏手部运动期间获得的真实MEG数据集的实验中得到了验证。
