[Eeglablist] re-reference with EGI data

[Tarik S Bel-Bahar]

corrected version below

just some partial answers, hope this helps.
> Please let the list know when you find out more.
>
> FidNz = the fiducial marker near the nose (nasion),
>


> the others are the left and right fiducials markers near the ears
> These are some of the basic markers for co-registration across heads/nets,
>
   basic landmarks that can be very useful.
   In your case it seems you do not have individual electrode positions

> Check this image http://sccn.ucsd.edu/eeglab/dipfittut/coregister3.gif
> and the eeglab wiki for more info.
> These labels are often automatically detected by eeglab, and yes, they
> are the three "hidden channels" at initial import.
>
> Check the eeglab list archives for the link to EGI's multiple
> formats.(search EGI and/or Netstation)
> Make sure you are using the right electrode locations for nets you used
> (hydrocel probably).
> If you export your EGI files with a reference channel, then you should use
> the EGI locations
> file that has the 128 + the reference channel, and so on.
> Note also that the electrode location file that eeglab selects
> may not be exactly the right one, so better to feed it the one you know is
> right.
>
> see below for more info
>
>    - [Eeglablist] .ced file or list of electrode labels for 128-channel
>    egi sensor net <http://sccn.ucsd.edu/pipermail/eeglablist/2012/005041.html>
>      *Tarik S Bel-Bahar*
>
>
>
>
>
>
>
> On Fri, Aug 24, 2012 at 12:09 PM, Joshua Hartshorne <
> jkhartshorne at gmail.com> wrote:
>
>> I have EGI data recorded with a 128 electrode cap (vertex reference). I
>> exported it to EEGLab and included the reference in the export (I used the
>> multiple file format).
>>
>> EEGLab seems to recognize everything fine and includes 128 electrodes in
>> the data, though when I go to "edit channel locations", I see 132 channels.
>> The last one is my reference channel, labeled correctly as Cz. Though it's
>> channel type is listed as "REF", no Reference is listed in the pop-up
>> window (the section below the panel of "channel type") for any channel. I
>> have no idea what channels 129-131 are (they are labeled FidNz, FidT9, and
>> FidT10).
>>
>> So I want to re-reference. If I check "compute average reference", I
>> don't have the option of retaining the old reference channel, which seems
>> odd. If I click on the "..." button after "Add current reference channel
>> back to the data", I get an error (??? Error using ==> waitfor Error while
>> evaluating uicontrol Callback). From the wiki, I understand I should have
>> gotten a list. Manually setting reference to "Cz" or "132" using the "edit
>> channel info" window for channels 1:128 doesn't fix this problem.
>>
>> However, if I leave all that blank, I "successfully" re-reference to
>> average reference. That is, I don't get an error, though I'm not sure how
>> to determine whether it worked correctly or not.
>>
>> What I'd really like to do is re-reference to the average of the mastoids
>> (channels 57 and 101), which would aid comparison with another dataset that
>> was collected on different equipment with fewer electrodes. But the wiki
>> suggests that I have to do this by going through average reference first
>> (really?), so I wanted to make sure I had that much right first.
>>
>> In any case, I assume that if I list two electrodes in the "re-reference
>> data to channel(s):" box that it will automatically compute the average of
>> those two. I tried doing that (both with and without going through average
>> reference), and I notice that channels 57 and 101 are *not* listed as "REF"
>> in "Channel type" after doing this, while Cz is still listed as "REF",
>> though "Reference" is now listed as "E57 E101".
>>
>> I appreciate any help.
>> Josh Hartshorne
>>
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>
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