[Eeglablist] ICA of concatenated subjects?

[Louis Renoult]

Hi Ana,
 The single subject approach and the group approach have their respective supporters. To sum up:

• Single Subject Approach:
- First, individual ICA decomposition (e.g., 128 ICs by subjects for a 128 channel recording)
- Then, group analysis: clustering of similar ICs based on various criteria: similarity of scalp maps, ERPs, dipole locations, etc.
- Potential difficulties: Processing time (data-overload?), choice of the number of clusters and method of clustering.
 References: all the main EEGLAB papers and tutorials: http://sccn.ucsd.edu/eeglab/eeglabtut.html

• Group Approach:
- First, concatenation of all subjects for each condition
- Then single ICA
- Main Problem: dealing with inter-individual differences in brain anatomy/physiology ("my Cz is not your Cz")
People often run PCA first and retain the largest factors before ICA… which may result in the same difficulty for choosing the number of factors
References:
Dien et al., (2007 in Human Brain Mapping)
Eichele et al., (2008, 2009 in International Journal of Psychophysiology): parallel EEG-fMRI ICA,  see also their “Group ICA of EEG Toolbox” (EEGIFT):
http://icatb.sourceforge.net/groupica.htm

Best,
Louis Renoult

________________________________
From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu] on behalf of Ana Navarro Cebrian [anavarrocebrian at gmail.com]
Sent: Wednesday, April 10, 2013 7:35 PM
To: eeglablist at sccn.ucsd.edu
Subject: [Eeglablist] ICA of concatenated subjects?

Hi,
I was wondering if there is any problem with trying ICA for the entire group of subjects (as it's usually done in fMRI) instead of running ICA for each individual subject and then finding the common components with a cluster analysis. I thought it could be as simple as concatenating all the subject's data, but I tried it and the ICA components that I got from it are looking quite bad. They look as if the data were really noisy. I understand that there is more variability, but this data is very clean and I expected something better. Am I missing something? I appreciate any help.
Many thanks,
Ana


Avis de confidentialité: L'information contenue dans ce courriel peut être confidentielle et/ou privilégiée. Si vous n’êtes pas le destinataire de ce message, veuillez le détruire et en informer l’expéditeur. Il est interdit de copier ou de modifier ce courriel sans autorisation de l’auteur. Le Douglas n’assume aucune responsabilité du contenu des messages personnels.

Notice of confidentiality: The information contained in this email may be confidential and/or privileged. If you are not the intended recipient of this message, please destroy it and advise the sender. It is forbidden to copy or modify this email without the author's consent. The Douglas is not responsible for the content of personal messages.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20130411/3d25c6df/attachment.html>