source analysis attempt using DICS method

[Jan Mathijs Schoffelen]

Dear Brian,



Allow me to point you to a quite related problem which has been posted by
Nathan about a month ago. I think it was the beginning of March. You can
browse through the discussion list's history when you go to the
fieldtrip-website and click around a bit at the appropriate links. Even
though the question here was related to LCMV-beamformer, the problems might
have the same cause.

Following Nathan's thread, a very likely cause is the incorrect
specification of cfg.mriunits, and cfg.sourceunits prior to calling
sourceinterpolate (I did not find back in the code you sent in your mail
that you actually called it, but I assume you did). If not specified,
fieldtrip puts cfg.mriunits to 'mm', and cfg.sourceunits to 'cm'. There
might be a discrepancy in your data there. Perhaps you even explicitly have
to check, whether your headmodel (in hdmfile) is defined in cm. At least the
dipole-grid on which sourceanalysis performs the beamformer-scanning is
defined in cm, and I guess the units should be identical here as well.



Good luck,



Jan-Mathijs



  _____

From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Brian Roach
Sent: Thursday, March 29, 2007 1:08 AM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] source analysis attempt using DICS method



Attached is the output from a call to sourceinterp on source analysis output
data.  I am trying to use the DICS method, but my output looks nothing like
the tutorial pictures.  I am including what I believe to be the relevant
code, and advice on the source of my mistake(s) would be appreciated:

[EEG com] = pop_loadbv('/home/bjr39/FTsource', 'B22001hal.vhdr')
EEG1 = pop_select(EEG)
help eeglab2fieldtrip
data = eeglab2fieldtrip(EEG1, 'preprocessing')

%%%
there is some code which I have not included that string matches my
electrodes and uses coordinate that put the sites in MNI space according to
the coordinates listed
here:http://oase.uci.ru.nl/~roberto/electrode/realistic_1005.txt
%%%

cfg.output     = 'powandcsd';
cfg.method     = 'mtmfft';
cfg.foilim     = [5 100];
cfg.tapsmofrq  = 2;
cfg.foilim     = [35 45];
freq = freqanalysis(cfg, data)

cfg = [];
cfg.method = 'dics';
cfg.frequency = 40;
cfg.hdmfile = '/home/bjr39/FTsource/vol.mat';
cfg.resolution = 2
pack;source = sourceanalysis(cfg, freq)

sourcePost = sourcedescriptives([], source)

cfg =[];
cfg.downsample = 2;
cfg.funparameter = 'nai';
cfg.colmin = 'auto';
cfg.colmax = 'auto';
sourcePostF = source2full(sourcePost);
sliceinterp(cfg,sourceInterp);


I can share more info if it will help, related to the size of different data
structures, or whatever anyone would need to know.  I followed the guide for
head model creation and plotted it at various points (one plot previously
posted to the list).  Could a poor head model create this problem?

thanks,
Brian

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