[Eeglablist] imported BrainVision data: finding the reference electrode
Maren Grigutsch
grigu at cbs.mpg.de
Wed Sep 26 03:31:43 PDT 2012
Hi Ricardo,
I think you can do the re-referencing in EEGLAB. The trick is to tell
EEGLAB what your recording reference was. I guess the corresponding
command is something like this:
EEG = pop_editset(EEG, 'ref', 'M1');
Without that information, "add current reference channel to the data"
won't work because it's unclear which channel the reference was.
Best,
Maren
Ricardo Moura wrote:
> Hi Steve,
>
> I have just done what you said, and when I plot the data, the signal
> in the right mastoid electrode is turned to a flat line. It seems that
> all of the data was re-referenced only to this channel. If I try "add
> current reference channel to the data", I get the error message again
> (there are no reference channels)...
>
> Do you know if there is a way to export the data already re-referenced
> from the BrainVision analyzer? Now I am trying the analysis using the
> raw data.
>
> Thank you very much once again.
>
> Best,
> Ricardo
>
> On 24 September 2012 23:59, Stephen Politzer-Ahles
> <politzerahless at gmail.com <mailto:politzerahless at gmail.com>> wrote:
>
> Hi Ricardo,
>
> If I'm understanding correctly, you should be able to get the
> average mastoid by choosing right mastoid as your reference and
> selecting "retain old reference channels". This should average
> together the right mastoid with the current reference (the left
> mastoid) and compute a new reference based on that average.
>
> Best,
> Steve
>
>
> On Mon, Sep 24, 2012 at 9:39 PM, Ricardo Moura
> <ricardoojm at gmail.com <mailto:ricardoojm at gmail.com>> wrote:
>
> Hi,
> Thanks for your answer.
> The reference channels were recorded at the left (recording
> reference) and right (recorded as a normal eeg channel)
> mastoids. The right reference is available when I open the
> data in EEG lab, but not the recording reference. The
> reference channel always appear as "unknown" at the main
> eeglab window, and when I go to the "channel locations", it
> only shows me 64 electrodes (the 65th electrode, which would
> be the recording reference, is missing). This is a problem
> because I need this channel in order to re-reference the data
> to linked-ears (don't I?). But I don't need to use it as an
> active electrode.
>
> So when I try the "Add current reference channel back into
> the data" , I allways have the following message: "there are
> no reference channel defined, add it using the channel locations".
>
>
> Any idea about how to recover this channel (in case I really
> need it to perform the linked-ears reference)?
>
> Best,
> Ricardo
>
>
> On 24 September 2012 14:50, Stephen Politzer-Ahles
> <politzerahless at gmail.com <mailto:politzerahless at gmail.com>>
> wrote:
>
> Hi Ricardo,
>
> May I ask what your reference was? In my experience using
> Brain Vision data, the recording reference (in my case it
> was on the nose) was just not included in the data that I
> imported to EEGLAB. This wasn't a problem for me because I
> wasn't interested in analyzing that electrode anyway after
> I re-referenced; but it might matter for you if your
> reference is something that you care about as an active
> electrode, like Cz. You may be able to get that channel
> back by using the "Add current reference channel back into
> the data" command and specifying its location (but I
> haven't tried that myself with BV).
>
> Best,
> Steve
>
> On Mon, Sep 24, 2012 at 8:55 AM, Ricardo Moura
> <ricardoojm at gmail.com <mailto:ricardoojm at gmail.com>> wrote:
>
> Dear all,
>
> I am new to the EEGLab. Now I am trying to analyze
> data that were recorded using the BrainVision
> recorder, but I never find the reference electrode.
> Going to "Channel Locations" only shows me the EEG
> electrodes. It is a problem for me because I want to
> re-reference the eeg signal to the linked-ears. The
> second reference electrode is always there (once it
> was recorded as a regular eeg electrode), but not the
> actual reference.
>
> I would appreciate any help,
> Best,
> Ricardo Moura
>
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>
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/ <http://people.ku.edu/%7Esjpa/>
>
>
>
>
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/ <http://people.ku.edu/%7Esjpa/>
>
>
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--
Max Planck Institute for Human Cognitive and Brain Sciences
Dipl.-Phys. Maren Grigutsch mailto:grigu at cbs.mpg.de
Stephanstr.1a http://www.cbs.mpg.de
04103 Leipzig, Germany phone/fax: +49 341 9940-136/-2260
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