[Eeglablist] re-referencing to the average of both mastoids

[Sarnthein Johannes]

Hi Steve,

this is how we do the re-referencing to the average of both mastoids:

% re-reference 61 cephalic channels to (M1+M2)/2: chans 40 and 60, 
% exclude from re-referencing HEOG, VEOG, EMG: chans 62, 63 and 64
% discard mastoid recordings: 'keepref', 'off'
EEG.data = reref(EEG.data, [40 60], 'method', 'withref', 'refloc',{
'CPz',180,0.1},...
'exclude', [62:64],'keepref', 'off');

% load special location file
EEG.chanlocs=pop_chanedit(EEG.chanlocs, 'load',{ 'CPzatend.loc',
'filetype',''});

This method works, but with one drawback: 
The physical reference during recording (in our case electrode CPz)
is listed only as the last channel EEG.data(end,:).
Unfortunately I could not manage to list CPz between CP1 and CP2.
So EEG.data(end,:) has to be labeled accordingly in CPzatend.loc.
This need a little book-keeping in the later analysis,
but otherwise works fine.

Best,
Johannes



________________________________

Von: eeglablist-bounces at sccn.ucsd.edu
[mailto:eeglablist-bounces at sccn.ucsd.edu] Im Auftrag von Steve Fleming
Gesendet: Freitag, 19. Januar 2007 19:28
An: eeglablist at sccn.ucsd.edu
Betreff: [Eeglablist] rereferencing problems



Hello all,

 

I too have a rereferencing question. I would like to re-rereference to
linked mastoids, but at the moment my data has the left mastoid as a
common reference. Is there a way of instructing the pop_reref or reref
functions to compute an average of both the common and another channel?

 

At the moment the only way I can think of doing it is to re-reference
twice, first to an arbitrary channel (while keeping the original mastoid
common in the data) and then to both mastoid channels.

Any advice would be greatly appreciated!

 

Cheers

Steve