[Eeglablist] ICA error

[Erika Nyhus]

Hi Tarik and Makoto,

Thanks, this is very helpful.  Based on your recommendations I have solved
my ICA error.  When I appended a channel and re-referenced to the average
reference and add the reference channel back to the data I got the ICA
error, but if I add a channel and re-reference to the average reference and
add the reference channel back to the data it runs fine.

Erika

On Mon, Jan 8, 2018 at 3:19 PM, Tarik S Bel-Bahar <tarikbelbahar at gmail.com>
wrote:

> Hi Erica, this looks like it's a bug but not one that usually comes up. It
> seems that one should be able to select a smaller number of channels to be
> run.
> SInce it is repeatable and you haven't found a solution, please log it
> into the eeglab bugzilla. Some of my thoughts below echo Makoto's.
>
> It may not be an error, but rather eeglab basically requesting that the
> channels you put in be the same as the number of channels in the dataset.
> In the meantime you may want to arrange your data differently to work
> around this until there is a fix or explanation.
> Some other quick thoughts below, not sure if they will help, thanks for
> giving suggestions a try if you have time.
> Cheers!
>
>
> ********Extra thoughts for Erika
>
> If you haven't had a chance, to,  you may want to try    a)delete a
> channel before ICA to reduce rank after re-referencing
>  or b) reduce rank by reducing the dimensionality of the ICA by adding a
> "pca" flag in the function to number of channels minus one.
>
> You may be able to solve the problem by either 1) delete a single channel
> right before the ICA step (and running 1:63)
> or 2) not adding back the reference channel before ICA. Both together may
> work too.
>
> What happens when you just don't add in the reference channel? This might
> be creating the mismatch.
> I would also step through more closely between the channel count and
> labels variables in the EEG structure to see if there was a mismatch in
> eeglab's expectations.
> See also the sub-structures of EEG that update with reference channel
> information.
> Each step should be doable via GUI, and if you are using matlab scripts
> there should be a checked to make sure commands look like those derived
> from eegh history of commands run via the eeglab GUI.
>
> Try triple-checking to make sure you "adding in the reference channel" and
> "doing average reference" correctly (should all work through the gui)
>
> Further, it's  important to know is how results look when you run the 1:64
> ICA.
>
> Please see if following sequence works if you get a chance:
> 1. Take the original raw file with channel locations loaded (load 63
> channels)
> 2. Remove bad/worst channels and bad/worst periods.
> 3. Interpolate/add the single reference channel (possibly do after ICA or
> not at all)
> 3. Run ICA on all the remaining good channels (should be at least 45 and
> well distributed)
> 4. Interpolate bad channels (if computing EEG/ERP metrics at channel level
> rather than ICA-level.
> 5. Stay in ICA space, and compare/analyze similar ICs across your
> experiment's design.
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-- 
Erika Nyhus, Ph.D.
Department of Psychology and Program in Neuroscience
6900 College Station
Bowdoin College
Brunswick, ME 04011
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