[FieldTrip] Error in DICS Source Localization (Beamformer)

Helen L. Wieffering hwieffer at bowdoin.edu
Mon Jul 20 21:52:39 CEST 2015

Dear Fieldtrip Users,

In attempting to use Beamformer source localization, I get an error when computing ft_sourceanalysis with the code below:

cfg = [];
cfg.method = 'dics';
cfg.frequency = 6;
cfg.elecfile = 'GSN_HydroCel_129_short.sfp';
cfg.vol = vol;
cfg.dics.projectnoise = 'yes';
cfg.dics.lambda = '5%';
cfg.dics.keepfilter = 'yes';
cfg.dics.realfilter = 'yes';
sourceAll = ft_sourceanalysis(cfg, freqAll);

the call to "ft_selectdata" took 0 seconds and required the additional allocation of an estimated 0 MB
using headmodel specified in the configuration
reading electrodes from file 'GSN_HydroCel_129_short.sfp'
converting units from 'cm' to 'mm'
determining source compartment (1)
projecting electrodes on skin surface
combining electrode transfer and system matrix
creating dipole grid based on inward-shifted brain surface from volume conductor model
using headmodel specified in the configuration
using gradiometers specified in the configuration
642 dipoles inside, 0 dipoles outside brain
the call to "ft_prepare_sourcemodel" took 0 seconds and required the additional allocation of an estimated 42 MB
selection crsspctrm along dimension 3

Attempted to access noise(0); index must be a positive integer or logical.

Error in beamformer_dics (line 211)
    noise = noise(end);

Error in ft_sourceanalysis (line 662)
          dip(i) = beamformer_dics(grid, sens, vol, [],  squeeze(Cf(i,:,:)), optarg{:});

I note that it runs without errors when I change cfg.dics.projectnoise to 'no' - but what implications does that bring? I find with that change I can make it through the rest of the Beamformer tutorial (the section on contrasting conditions) without explicit errors, but I nevertheless receive the following messages, following which my plotted figure is simply blank! Something is going wrong, I think.

sourceDiffInt = ft_sourceinterpolate(cfg, sourceDiff, mri);
Warning: use cfg.parameter='pow' instead of cfg.parameter='avg.pow'
> In ft_checkconfig (line 139)
  In ft_sourceinterpolate (line 119)

ft_sourceplot(cfg, sourceDiffInt);
Warning: use cfg.funparameter='pow' instead of cfg.funparameter='avg.pow'
> In ft_checkconfig (line 139)
  In ft_sourceplot (line 210)
Warning: use cfg.maskparameter='pow' instead of cfg.maskparameter='avg.pow'
> In ft_checkconfig (line 139)
  In ft_sourceplot (line 213)
the input is segmented volume data with dimensions [128 128 128]
not plotting anatomy
Warning: could not determine dimord of "pow" in the following data
> In getdimord (line 516)
  In ft_sourceplot (line 390)

Anyone know what might be the problem? Thanks very much!

Helen Wieffering
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