[Eeglablist] quick questions about use/interpretation of duplicate/triplicate IC decompositions

[Tarik S Bel-Bahar]

Greetings,

Quick questions below about use and interpretation of ICA decompositions,
from a dense eeg experiment presenting faces on each trial.
If anyone has run across problems of this sort, and/or can envision
 a pragmatic solution path, it would be much appreciated!
**this general topic may have come up on eeglablist before,
but I had some trouble searching through the whole archive easily.
**a sample file,examples, and more information are available upon request,
but the information below should be enough details to attract a solution.

****Description of issue*
In our AMICA decompositions, we are getting several similar ICs
 (e.g., P100 topography), which are associated with
 different parts of the recording session,
with one IC being active only on the first half of trials,
and the second being active in the second set of trials.
In other words, the erpimage of each component shows only
activity in the first half or second half of trials.

It seems that "rewetting" of electrodes in the middle of the session
led to changes in electrode placement, which leads to having these
duplicate ICs,
due to spatial stationarity assumptions in ICA algorithms.

A similar issue comes up when examining ICs from three
different recording sessions of one subject, with triplets of ICs showing
up,
but again, with each IC being active for only one session's trials, but not
the rest of the trials.

*
*
****My basic questions are: *
*What are the fastest and most pragmatic solutions at this point ?*

A. Is there a method to safely (and defendably) merge the double
or triple ICs within each subject session ?

B. If I just use the ICs as they are, and simply cluster them within each
recording session,
how do I best account for the fact that IC activation
(for each double/triple IC) occurs only in a half or a third of trials,
either for within subject or across-subject comparisons ?


All the best,
Tarik
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