[FieldTrip] problems with ft_dipolesimulation

[Rojas, Don]

Dear Fieldtrippers,

I'm having difficulties trying to construct a simulated dataset using ft_dipolesimulation. I am simulating using a 4D MEG sensor array, read in from an existing dataset (this dataset poses no particular problems when used in other FT routines, but I'm only using the headshape and the gradiometer location/orientation info for the headmodel and simulation anyway). The problem is that I am getting values of zero in all channels at all time points in the simulated set. No errors are generated, but there is a message about the RMS value of simulated data is 0 when ft_dipolesimulation is run - no surprise there. Here is my code:

% read 4D file
file = 'c,rfhp0.1Hz';
hdr  = ft_read_header(file);
hs   = ft_read_headshape('hs_file');



% create a single sphere conductor model from 4D dataset
cfg                 = [];
cfg.grad            = hdr.grad;
cfg.headshape       = hs.pnt;
cfg.singlesphere    = 'yes';
ft_sphere           = ft_prepare_localspheres(cfg);



% simulate a dipole
cfg_sim.vol            = ft_sphere;
cfg_sim.grad           = hdr.grad;
cfg_sim.fsample        = hdr.Fs;
cfg_sim.relnoise       = .1;
cfg_sim.dip.frequency  = 20;
cfg_sim.dip.phase      = pi/2; % 90 degree phase
cfg_sim.triallength    = 1;
cfg_sim.ntrials        = 50;
cfg_sim.dip.pos        = [0 -.05 .05]; % position in meters
cfg_sim.dip.mom        = [0 0 -1]';
sim                     = ft_dipolesimulation(cfg_sim);

Also, I have run the script from the following example:

http://fieldtrip.fcdonders.nl/example/compute_forward_simulated_data_and_apply_a_dipole_fit

The simulated data in that example also has no data other than zeros in all channels. So, I don't think this is due to my code per se, which was adapted from that example. My MATLAB version is 2009b (maci64) and I've tried this in several FT versions, including the 20110328 version, all of which produce the same results.

Any ideas?

Don

-----------------------
Don Rojas, Ph.D.
Associate Professor of Psychiatry
U. of Colorado Denver Anschutz Medical Campus
Director, UCD Magnetoencephalography Lab
13001 E. 17th Pl F546
Aurora, CO 80045
USA
303-724-4994

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20110329/4ce7f115/attachment-0001.html>