[FieldTrip] Align EEG electrode positions to BEM headmodel Question

Juan Pablo Neira jpnv2006 at gmail.com
Thu Feb 16 17:35:28 CET 2012


I am trying to align EEG electrodes to an individual MRI and a BEM
model.  I am using the example:

"Align EEG electrode positions to BEM headmodel"

But I am having the next problem in "% align using fiducials" part:

* Template structure (label, chanpos and elecpos) - sens_t structure
(label, chanpos and elecpos)

elec_mni.label = {'Nz', 'LPA', 'RPA'};
elec_mni.chanpos = [
elec_mni.elecpos = [
elec_mni.unit = 'mm';

% align using fiducials

cfg = [];
cfg.method = 'fiducial';
cfg.template= elec_mni;
cfg.elec     = sens_t;
cfg.casesensitive  = 'no';%'yes' or 'no'
sens_aligned = ft_electroderealign(cfg);

%Error message:
??? Subscripted assignment between dissimilar structures.

Error in ==> ft_electroderealign at 183
    tmp(i) = ft_datatype_sens(template(i)); % ensure up-to-date sensor
    descriptions (Oct 2011)

I have some questions that maybe can help to find the error:
-  According to the example in the webpage, there are 2 functions from
the private directory used:  electrodenormalize.m & warp_apply.m, but
electrodenormalize.m never was used.  Also in "% align using
fiducials" the method used was  'realignfiducial', but that method is
not available in electroderealign function.  Is it possible the
example is using the wrong function?

-  How should be the structure of the fiducials in the main sensor
structure (sens_t).  As 3 more electrodes (label+fid, chanpos+fid and
elecpos+fid) or in a different place, for example sens_t.fid.pnt and

By the way I am using Matlab 2011 and fieldtrip version 20120208

Best regards and thanks for the help.

Jua Pablo Neira Vesga
Christian Albrechts Universität
Clinic Kiel, Germany

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