[Eeglablist] online reference

Andreas Widmann widmann at uni-leipzig.de
Sat Apr 25 09:17:35 PDT 2015


> To clarify, I have 31 channels + ref (Cz) + ground. So 33 in total.
Good!

> I added Cz to my channel locations and selected "add current reference channel back to data" without re-referencing to anything else.
Sorry, could you please clarify how you use the "add current reference channel back to data“-option *without* actually re-referencing? To my understanding this should be impossible. Either the „Compute average reference“ or the „Re-reference data to channel(s)“-option is always selected in the pop_reref GUI. In case „Compute average reference“ was selected, the data were re-referenced to the mean of all channels.

> I can now see Cz, but it isn't a flat line. Am I incorrect in thinking that it should be totally flat?
Without re-referencing the implicit reference should indeed be a flat line/zero. 

Hope this helps!
Andreas

> Thanks,
> Brittany
> 
> On Thu, Apr 23, 2015 at 5:29 AM, Andreas Widmann <widmann at uni-leipzig.de> wrote:
> Hi Brittany,
> 
> this sounds like two different problems:
> If you record from 32 channels + Ref + Ground the imported file should have 32 channels (but not your Cz Ref channel). Please reconfirm that your Pycorder setup really records from 32 data channels (34 electrodes). In case there is really a channel missing, please, submit a bug report to the bugtracker including a short sample file.
> 
> If you want to keep the implicit online reference (Cz) as a new channel after re-referencing the data to another channel you have to use the „Add current reference channel back to the data“-option (GUI; 'refloc‘ on command line). To use this option you have to first append a (Cz-) channel in the GUI channel editor (appearing in EEG.chaninfo.nodatchans) which you can subsequently select during re-referencing. The „new“ Cz-channel is the inverse of the channel the data were re-referenced to (now missing in the data or being flat if "Retain old reference channels in data“ was selected).
> 
> Please note that the „Add current reference channel back to the data“-option should not be used for systems where common mode rejection is applied offline (e.g. Biosemi).
> 
> Hope this helps,
> Andreas
> 
> > Am 22.04.2015 um 21:59 schrieb Brittany Alperin <balperin07 at gmail.com>:
> >
> > Hello
> >
> > I'm using a 32 channel brain vision system and am recording with PyCorder. When I import my data using the brain vision recorder plugin, only 31 channels are present. I'm recording with Cz as an online reference and Cz is the channel that is missing. I can re-reference, but Cz is still absent.
> >
> > Has anyone had an issue with recording with an online reference and not having that data import into EEGlab? Or does anyone have a different way to import brain vision data?
> >
> > Thanks,
> > Brittany
> >
> >
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