[Eeglablist] ICA of concatenated subjects?

[Stephen Politzer-Ahles]

Hi Ana,

I'm not sure if this answers the 'why' of your question, but in my
experience it is not common to run ICA on multiple subjects--it's always
been recommended to me that a separate ICA decompostion should be done for
each subject, as you are describing. In fact, even if the same subject came
in for multiple sessions, common practice (as far as I have been told) is
to do a separate ICA composition for each time the subject came in. (One
reason for this is because if the subject takes the cap off and then comes
back later and puts it on again, the cap might be in a slightly different
place--in fact, in the past when I've tried concatenating multiple sessions
of a single subject and doing a single ICA decomposition for fun, I
generally get two of every component, e.g. one component for blinks in
session 1 and another component for blinks in session 2, etc.)

I haven't ever done ICA on fMRI data, so I'm not sure what techniques fMRI
researchers do to be able to do ICA on group data; maybe someone else on
the list can give you more information about that.

Best,
Steve



On Wed, Apr 10, 2013 at 6:35 PM, Ana Navarro Cebrian <
anavarrocebrian at gmail.com> wrote:

> 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
>
>
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-- 
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/
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