[Eeglablist] channel cross-coherence

[Daniel Mathalon]

Dear EEGLAB gurus,

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?

Thanks,

Dan Mathalon

>I am also wondering about this.
>This publication 
>(http://www.sccn.ucsd.edu/eeglab/download/eeglab_jnm03.pdf) states:
>
>ERCOH. EEGLAB function crossf() computes eventrelated
>coherence (ERCOH) between two channel or
>component activities in sets of trials to determine the
>degree of synchronization between the two activity
>measures. As for ITC, both phase coherence
>(ERPCOH) and linear coherence (ERLCOH) measures
>are supported. Other phase coherence measures have
>not (yet) been included in EEGLAB (e.g., Lachaux et
>al., 1999).
>
>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?
>
>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.
>
>thanks,
>Brian
>
>At 08:03 PM 5/12/2006, Kline, Keith A wrote:
>
>>Regarding the channel cross-coherence function:
>>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?
>>Thanks,
>>Keith
>>
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>
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-- 
Daniel H. Mathalon, Ph.D., M.D.
Associate Professor of Psychiatry
Yale University School of Medicine

Mailing Address:	Psychiatry Service 116a		Office Phone: 
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