Dipole modeling & averaged CTF data

Kambiz Tavabi kambiz.tavabi at UNI-MUENSTER.DE
Wed Aug 2 12:03:26 CEST 2006


Dear FieldTrippers,
I am relatively ignorant with MATLAB and even more so with FIELDTRIP.
With that said I would like to implement ECD modeling with preprocessed
averaged CTF MEG data for the evoked gamma auditory response using
MNI-aligned grids in individual head-space for the dipole scans.
For starting I am beginning with the following example scripts from the
FT-Docs; Fit a dipole to the tactile ERF after mechanical stimulation &
Create MNI-aligned grids in individual head-space. So far I am facing
these issues:
(i) Since I am working with averaged data I would like to skip the
TIMELOCKANALYSIS, however when I do so I cannot get the butterfly plot
of the ERF because I am unable to pass 'time' & 'avg' to
plot(1000*avg.time, avg.avg) directly from data.trial:{[274x150 double]}
or data.time:{[1x150 double]}, since function 'mtimes' is not defined
for values of class 'cell'.
(ii) I proceed to use TIMELOCKANALYSIS and obtain the avg structure using...
cfg.channel = 'MEG';
cfg.latancy = ['prestim' 'poststim'];
cfg.covariance = 'no';
cfg.blcovariance = 'no';
cfg.keeptrials = 'yes';
cfg.normalizevar = 'N';
cfg.removemean = 'no';
cfg.vartrllength = 2;
cfg.vartrllength = 2;
avg = timelockanalysis(cfg, data);
getting the warning Warning: Divide by zero.
In timelockanalysis at 536 since I only have one trial.
The butterfly plot now looks reasonable. To fit dipoles I use...
cfg = [];
cfg.latency = [0.045 0.120];
cfg.numdipoles = 2;
cfg.symmetry = [];
cfg.model='regional';
cfg.hdmfile = 'A0109.hdm';
cfg.feedback = 'textbar';
cfg.resolution = 2;
dipeGBR = dipolefitting(cfg, avg);
and I get...
??? Error using ==> dipolefitting
dipole scanning is only possible for a single dipole or a symmetric
dipole pair.
 From what I understand I am using symmetric dipoles, which is fine to
begin with but ultimately I would like to used two regional sources free
of the symmetry constraint.
What are my options?
Thanks for your time.
Kambiz
--
============================================
Kambiz Tavabi, Dipl. Psych., MS.

Institute for Biomagnetism and Biosignalanalysis
Muenster University Hospital

Malmedyweg 15
D-48149 Muenster
Germany

phone:   +49-(0)251-83-56884
fax:     +49-(0)251-83-56874
e-Mail: Kambiz.Tavabi at uni-muenster.de

============================================
-------------- next part --------------
A non-text attachment was scrubbed...
Name: kambiz.tavabi.vcf
Type: text/x-vcard
Size: 429 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20060802/070d25ad/attachment.vcf>


More information about the fieldtrip mailing list