[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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