[Eeglablist] ICA "adds" noise?

[Tarik S Bel-Bahar]

Greetings Kristina,

First off, thanks for your lucid and informative email. You provide a lot of
useful detail that makes it easier to make some suggestions.
Working with precious pediatric data of course has some unique issues,
and I think you can easily find out about these approaches
by looking at existing work with infant and pediatric eeg (including #
of trial issues).

..I'm not sure if you specified you had a problem with rank in your
data, but as Matt suggested
it is useful to make sure you are operating and interpreting your ICA correctly.

...I would urge to check that this is a pattern across all subjects or
only some.
If across all, then it could a hardware or child development issue.
If not, then it could be a subset of your 2 year olds where doing
something special.

I don't have any other useful direct thoughts, but further below
I suggest some things that came to mind that you might want to try out,
having worked with egi systems a bit.

Best wishes, and let us know what your final solution/interpretation is!

Tarik


********more thoughts here
consider the following:
dropping those bad or noisy channels (you can safely drop down to 90 channels
if you have to, as long as the channels are not all contiguous or take
out Major scalp regions
(such as all the occipital channels). Further, the validity and
cleanness of the ICA decomposition
depends partly on how much data that is free of extreme artifacts
that you have given to ICA  (ideally close to an hour or more).
I would suggest making sure you have really cleaned as well as you
can, using some
combination of functions and visual checking.
However it seems that your focus is on using ICA as a cleaning technique,
and you are not using doing your analyses on ICs themselves.

As an additional quick stringent test,
you can try to remove u to 40 channels, and leaving at least 30 minutes of data.
See if you can get interpretable information under those extreme conditions.

As an additional strategy (in case total data timepoints are too few)
is to reduce your electrode density
to 64 and restart your processing from there. If you recorded at
higher than 250 samples per second, you
might also consider reducing the sampling rate. Both strategies would
make things easier for ICA to
show you what might be going on in the eeg.

Regarding your channels, I've seen that kind of noisiness, very
similar to your first pic,
in infant, adolescent, and adult egi data, but not always. There are
multiple possible sources
for this, including muscle tension and electrode contact, and possibly
impedance as well.

Regarding removing components, yes you might be removing  some eeg
dynamics related to cognition.

Last, have you considered using the ICs themselves as your main
analysis points rather than
the reconstructed EEG data after removal of artifact ICs ? On the
other hand, there are many
studies that have successfully used ICA for cleaning. Cheers!