[Eeglablist] group level analysis
smakeig at ucsd.edu
Wed Mar 10 13:07:41 PST 2004
Some comments below. -Scott Makeig
Dénes Szucs wrote:
> Thank you for your earlier reply.
> Another question:
> To assess group level data is the process outlined below the right
> - perform ICA on individual data
> - identify relevant components (ICs) - ? according to their relation to
> stimulus onset and response time and similar power spectra?
Actually, different combinations of measures could be used - ERSPs,
dipole locations, ERPs or ERP images, etc.
> - identify identical relevant components across subjects -- ? Is it
> usually possible to identify components across subjects? Is there an
> objective method for this or the researcher has to "subjectively"
> judge the similarity of ICs?
See Makeig et al Science 2002 for an example of clustering components
across subjects. Many components do fall into clusters - of course, the
number of clusters may depend on how many subjects and components you
are clustering, as well as the 'dipolarity' of the clustered components,
the measures used, etc.
> - average identical component loadings across subjects
> --> is it possible this way to describe "group level" components?
Yes. See the Science paper at http://sccn.ucsd.edu/science2002.html
> - What if some components are missing in some persons? Sould
> one accept this as an indication of individual variability and simply
> use only components accepted as identical from other subjects? Or
> is it due to data quality not good enough?
I think your thinking here is correct - at least, to present knowledge.
There may be several reasons why a component type would not show up in
every subjects - insufficient number of channels, data quality, number
of time points, relative strength of the component activity, or absence
of a similar EEG-producing synchronization in some some subjects...
> It it possible to tell the
> quality of the data from the point of view of the ICA algorithm? (apart
> from the No of data points needed)
We are working a measure of ICA decomposition quality based on dipole
fitting - and hope to produce a manuscript soon.
> thank you, denes
> Denes Szucs
> Lecturer in Neuroscience and Education
> University of Cambridge, UK
> Shaftesbury Road, Cambridge, CB2 2BX, UK
> Tel: +44-(0)1223 369631
> Fax: +44-(0)1223 324421
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