Connectionists: Isolated effective coherence (iCoh): causal information flow excluding indirect paths (pre-print)

[Roberto D. Pascual-Marqui]

Dear Colleagues,
The following pre-print on a method for assessing the "isolated
effective coherence (iCoh)" might be of interest:

http://arxiv.org/abs/1402.4887

RD Pascual-Marqui, RJ Biscay, J Bosch-Bayard, D Lehmann, K Kochi, N
Yamada, T Kinoshita, N Sadato. Isolated effective coherence (iCoh):
causal information flow excluding indirect paths

Abstract: 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 (NCR), reflecting direct and indirect connections. Later, the
partial directed coherence (PDC) of Baccala and Sameshima (2001) was
proposed for direct connections. In this study the partial coherence
is estimated under a multivariate auto-regressive model, followed by
setting all irrelevant associations to zero, other than the particular
directional association of interest. This is the isolated effective
coherence (iCoh). It is shown that the NCR computed under these same
conditions is identical to the iCoh, thus enriching its
interpretability. In comparison with the iCoh, it is shown that the
PDC is affected by irrelevant connections to such an extent that it
can misrepresent the frequency response. Toy examples are included to
demonstrate these properties.

Sincerely,
Roberto
...
Roberto D. Pascual-Marqui, PhD, PD
The KEY Institute for Brain-Mind Research, University Hospital of
Psychiatry Zurich (Switzerland)
Department of Community Psychiatric Medicine, Shiga University of
Medical Science (Japan) (pascualm at belle.shiga-med.ac.jp)
[www.keyinst.uzh.ch/loreta] [www.researcherid.com/rid/A-2012-2008]