[Eeglablist] channel cross-coherence

[Brian Roach]

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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