[Eeglablist] online reference

[Brittany Alperin]

Hi Andreas

You're right. I forgot that compute average reference is automatically
checked, so I was looking at the data with the average reference instead of
a Cz reference.

I think I have this all cleared up now. Thanks for the help!

Brittany

On Sat, Apr 25, 2015 at 9:17 AM, Andreas Widmann <widmann at uni-leipzig.de>
wrote:

> > 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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