[Eeglablist] Combining Experiments with different Electrode numbers

[Marc Rosenkranz]

Hello John,

thank you, this seems like the answer to my problem. Sorry for the unclear phrasing of my question.

Best,
Marc

Von: RICHARDS, JOHN<mailto:RICHARDS at mailbox.sc.edu>
Gesendet: Donnerstag, 4. Juni 2020 18:21
An: Andreas Widmann<mailto:widmann at uni-leipzig.de>; Marc Rosenkranz<mailto:marc.rosenkranz at hotmail.de>
Cc: eeglablist at sccn.ucsd.edu<mailto:eeglablist at sccn.ucsd.edu>
Betreff: RE: [Eeglablist] Combining Experiments with different Electrode numbers

Andreas, Marc.

I think the purpose of the pop_interp is when you have missing channels and you want to interpolate the missing channels.

e.g.  you have a 90 channel recording, 17 channels are missing, you set these to missing, and use the other 66 channels to estimate the 17 missing channels.

I'm not sure that is what you are trying to do.  It sounds like you have a 96 channel setup, and a 64 channel setup, and want to change your 96 channel setup into the 64 channel setup.  The 96 and 64 have different chan locations.  In this case you want a function like spherical spline interpolation

[64-channel-EEG data]= Spline_interpolatation (64channel locations, 94channellocations, 94-channel data)

I have attached an example program for this.  The input are the EEG electrodes for two electrode sets and the data for one electrode set; the output is the data in the space of the second electrode set.  We use this routinely to go from 128-channel-EGI to the 10-10 system; also to interpolate 128 channels to a 30,000+ scalp mesh to plot ERP components on the scalp.  This program was adapted from programs in EEGLab (e.g., pop_interp) and ERP lab.

John



***********************************************
John E. Richards
Carolina Distinguished Professor
Department of Psychology
University of South Carolina
Columbia, SC  29208
Dept Phone: 803 777 2079
Fax: 803 777 9558
Email: richards-john at sc.edu
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-----Original Message-----
From: eeglablist [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Andreas Widmann
Sent: Thursday, June 4, 2020 8:04 AM
To: Marc Rosenkranz <marc.rosenkranz at hotmail.de>
Cc: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] Combining Experiments with different Electrode numbers

Hi Marc,

> thank you for the answer. So you would remove the channels from the 96 cap, to fit the 64 cap.
Hm, no, not necessarily. This was what you asked for: "I want to reduce the number of electrodes from the sets with 96 electrodes to 64. What do you think is the best way to do so? Is there are an eeglab function which can do this?"

> I hoped there would be a way or function, to fit the two cap sizes without loosing too much of the 96 caps‘ data.
You may interpolate the missing channels in the 64 channel datasets. There is also an EEGLAB function to do this:

EEG = pop_interp( EEG, chanlocs, 'spherical' ); where chanlocs is the EEG.chanlocs (sub-) structure of one of the 96 channel datasets. The channels present in chanlocs but missing in EEG are interpolated. Chanlocs must contain channel coordinates.

Personally, I do channel interpolation after data cleaning at the end of pre-processing.

Best,
Andreas

>  Best,
> Marc
>
> Von: Andreas Widmann
> Gesendet: Donnerstag, 4. Juni 2020 12:16
> An: Marc Rosenkranz
> Cc: eeglablist at sccn.ucsd.edu
> Betreff: Re: [Eeglablist] Combining Experiments with different
> Electrode numbers
>
> Hi Marc,
>
> > I would like to combine datasets of two experiments that used caps with different numbers of electrodes (96 and 64). I want to reduce the number of electrodes from the sets with 96 electrodes to 64. What do you think is the best way to do so? Is there are an eeglab function which can do this?
> EEG = pop_select( EEG, 'channel', channel list ) where channel list is
> a vector of channel indices or a cell array of channel names to retain in the new dataset.
>
> or
>
> EEG = pop_select( EEG, 'nochannel', channel list ) where channel list
> is a vector of channel indices or a  cell array of channel names to exclude from the new dataset.
>
> or
>
> „Select data“ in the GUI.
>
> Best,
> Andreas
>
> >
> > Thanks,
> > Marc
> >
> > _______________________________________________
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