[Eeglablist] Two ICA decompositions from one dataset- based on stage of working memory

Kathleen Van Benthem kathy_vanbenthem at carleton.ca
Thu Jun 26 15:53:25 PDT 2014

Hello All,
Has anyone tried to compare cluster locations between different conditions
within the same experimental session?
We are interested in locating dipoles associated specifically with
encoding versus maintenance during a working memory task, and are using
EEGLAB to conduct ICA and then PCA to examine dipoles.

Our first method did not give us much success--originally, we tried running
ICA on the entire dataset (including both encoding and maintenance
conditions), and epoched after ICA was run, so that we ended up with
separate files for the two conditions, each with the same ICA weights.
 When we ran STUDIES for each condition separately, we found the resulting
clusters were the same between encoding and maintenance conditions,
even though we expected differences to exist.

Because we didn't experience success with this method, we are wondering
whether it would be advisable to create two separate files for each
participant (from the same session) BEFORE running ICA-- One file would
contain EEG data epoched from the first condition (encoding--two seconds
per trial), and  the second EEG data epoched from the second
condition (maintenance--2 seconds per trial).   We would then run ICA
*separately* for each file and look to see if there were dipoles from the
encoding condition ICA that* consistently *were not in the
maintenance condition ICA results (and vice versa).   We have a priori
hypotheses of where maintenance activity would be taking place source-wise
as compared to where encoding would be taking place.   We are wondering if
it is advisable to compare dipoles that result from different ICA weights-
even when they are collected from the same session and just seconds apart.
 If there were unique sources of brain activity (dipoles) would it be
possible, from this design, to conclude that the unique dipoles were  in
fact associated with the different stages of the working memory task (all
other factors being held constant)?

Thanks for your thoughts on this.  We are aware that we need to make sure
we have large enough files in order to conduct ICA in the first place.

Kathleen (Kathy) Van Benthem M.H.S., B.Sc.O.T
Carleton University, Institute of Cognitive Science,  Ph.D. Candidate, ​

Sarah Cebulski
PhD candidate
Cognitive Science, Carleton University
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