[Eeglablist] Channels for ICA

[Tarik S Bel-Bahar]

​Hi Fabio, some notes below!

-you can take/use all 128 channels if you wish, some researchers cut off
the lowest channels across the head to reduce noise from face and neck.
Would bring you closer to 90 channels, and would remove the fuller coverage
of the head that the 128 channels provide.
-one usually puts into ICA whatever channels are not marked as
bad/dirty/noisy.
-for good ica, one does not want large patches of the montage to be missing
electrodes because of a "too-heavy" bad channel procedure, so there are
trade-offs in taking more or less channels.
-interpolation of bad channels before ICA is not recommended, as it adds
"extra info" into the data. Better to interpolate after ICA if you have to.
Remember that once you are working with ICs you have gone beyond channels,
and can focus on the ICs.
-after data has bad ICs removed, one can of course look at channels of
interest
-see makoto's pipeline, eeglab tutorial, and past eeglablist discussion on
this topic
-consider reviewing other approaches for ICA focusing on specific bands or
using different techniques including wavelets.







​

On Wed, Jul 18, 2018 at 2:18 PM, Giatsidis, Fabio <fabio_giatsidis at brown.edu
> wrote:

> Hello EEGLAB list,
>
> I have a (probably naive) question regarding ICA.
> I have been using an EGI 128-channel system to record resting states. I
> have been reading a bit about ICA, but it is still not clear to me:
> - whether I should or not choose the whole 128 channel set for running
> ICA, and
> - consequently, how I should *a priori* decide which channels to consider
> for ICA and which not.
>
> The recordings are ~2 minutes long and the sampling rate is 1000 Hz. I
> would like to keep as many channels as possible during pre-processing, and
> afterwards discard the ones I realize are not useful to my analysis - if
> this approach seems reasonable.
>
> Also:
> - if as a very first step I delete some clearly bad channels and then
> interpolate them to repopulate the original channel set, is it legit to
> include such interpolated channels during ICA?
>
> Thank you very much!
> Best,
> -Fabio
>
> --------------------------------
> *Fabio Giatsidis, M.D.*
> Resident in Neurology - University of Rome "Tor Vergata" - Rome, Italy
> Post-doctoral research fellow - Brown University - Providence, RI, USA
>
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