[Eeglablist] re-reference with EGI data

[Joshua Hartshorne]

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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