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--></style><title>Re: [Eeglablist] channel
cross-coherence</title></head><body>
<div>Dear EEGLAB gurus,</div>
<div><br></div>
<div>There were a couple of recent posts (see below) regarding
cross-channel coherence analyses. It is unclear what the
distinction is between phase coherence and linear coherence, and it
seems that neither of them calculates pure phase synchrony (as is done
with the Lachaux et al method). Can someone comment on how these
cross-channel coherences are calculated and whether there is a plan to
add a pure cross-channel phase synchrony measure to EEGLAB?</div>
<div><br></div>
<div>Thanks,</div>
<div><br>
Dan Mathalon</div>
<div><br></div>
<blockquote type="cite" cite>I am also wondering about this.<br>
This publication
(http://www.sccn.ucsd.edu/eeglab/download/eeglab_jnm03.pdf)
states:<br>
<br>
<font face="Arial"><i>ERCOH.</i> EEGLAB function<i> crossf</i>()
computes eventrelated<br>
coherence (ERCOH) between two channel or<br>
component activities in sets of trials to determine the<br>
degree of synchronization between the two activity<br>
measures. As for ITC, both phase coherence<br>
(ERPCOH) and linear coherence (ERLCOH) measures<br>
are supported. Other phase coherence measures have<br>
not (yet) been included in EEGLAB (e.g., Lachaux et<br>
al., 1999).<br>
<br>
Is the difference between the crossf measure and the Lachaux measure
that crossf takes amplitude/power into account and Lachaux's method
would only look at synchrony, not amplitude? Is the Lachaux
method going to be supported in this upcoming version of eeglab?<br>
<br>
Also, my math background is such that I am not entirely sure I
understand the difference between linear and phase options in crossf.
Is the critical difference that phase coherence is relative and linear
coherence is not. Maybe this would make more sense if I knew
where or why you would select one option over the other.<br>
<br>
thanks,<br>
Brian<br>
<br>
</font>At 08:03 PM 5/12/2006, Kline, Keith A wrote:<br>
<blockquote type="cite" cite>Regarding the channel cross-coherence
function:<br>
Does "coherence" represent synchronous changes in signal
*amplitude* between two channels, or something else? Since any
two signals containing X Hz activity would necessarily show phase
coherenece, albeit with an phase offset (as plotted in the lower
graph), I am assume the function's output represents coherently
modulated amplitude. Is this correct?<br>
Thanks,<br>
Keith<br>
<br>
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</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><br>
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<div><br></div>
<div><br></div>
<x-sigsep><pre>--
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<div>Daniel H. Mathalon, Ph.D., M.D.<br>
Associate Professor of Psychiatry<br>
Yale University School of Medicine<br>
<br>
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