孤立有效相干（iCoh）：排除间接路径的因果信息流
Isolated effective coherence (iCoh): causal information flow excluding indirect paths
摘要：
在真实世界系统中，多个时间序列测量是可用的，一个非常感兴趣的问题是系统内因果关系的估计。例如，电皮层信号用于研究大脑区域之间的功能连接，它们的方向性，连接的直接或间接性质以及频谱特性（例如优先传输哪些振荡）。最早的因果关系的频谱测量是Akaike（1968）关于噪声贡献率的开创性工作，反映了直接和间接的联系。后来，一个重大的突破是Baccala和Sameshima（2001）的直接联系的部分定向一致性。本研究的简单目的包括两个部分：（1）揭示部分定向相干性的主要问题，其中示出了它受到不相关连接的影响，以至于它可以错误地表示频率响应，从而违背了开发该措施的主要目的，以及（2）提供该问题的解决方案，即“孤立有效相干性”，其包括在多变量自回归模型下估计部分相干性，随后将所有无关关联设置为零，而不是感兴趣的特定方向关联。简单、现实的例子说明了部分定向连贯问题的严重性，以及孤立有效连贯的解决方案。为了进行可重复的研究，实现这里讨论的方法的软件代码（使用lazarus free-pascal“www.lazarus.freepascal.org“），包括作为文本文件的测试数据，可以在以下网站免费获得：https://sites.google.com/site/pascualmarqui/home/icoh-isolated-effective-coherence
英文摘要：
A problem of great interest in real world systems, where multiple time series measurements are available, is the estimation of the intra-system causal relations. For instance, electric cortical signals are used for studying functional connectivity between brain areas, their directionality, the direct or indirect nature of the connections, and the spectral characteristics (e.g. which oscillations are preferentially transmitted). The earliest spectral measure of causality was Akaike's (1968) seminal work on the noise contribution ratio, reflecting direct and indirect connections. Later, a major breakthrough was the partial directed coherence of Baccala and Sameshima (2001) for direct connections. The simple aim of this study consists of two parts: (1) To expose a major problem with the partial directed coherence, where it is shown that it is affected by irrelevant connections to such an extent that it can misrepresent the frequency response, thus defeating the main purpose for which the measure was developed, and (2) To provide a solution to this problem, namely the "isolated effective coherence", which consists of estimating the partial coherence under a multivariate auto-regressive model, followed by setting all irrelevant associations to zero, other than the particular directional association of interest. Simple, realistic, toy examples illustrate the severity of the problem with the partial directed coherence, and the solution achieved by the isolated effective coherence. For the sake of reproducible research, the software code implementing the methods discussed here (using lazarus free-pascal "www.lazarus.freepascal.org"), including the test data as text files, are freely available at: https://sites.google.com/site/pascualmarqui/home/icoh-isolated-effective-coherence
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
