[FieldTrip] Issues with: Sourcegrandaverage & Spatial Common Filter

Sara Aurtenetxe s.aurtenetxe at bcbl.eu
Sat Oct 10 13:00:08 CEST 2015

Dear all, 

I am working on the localization of oscillatory sources using beamforming 
The data are recorded with Elekta-Neuromag,
the source estimations are based on individual MNI-aligned grids
and the FT version is fieldtrip-20150701.

And I have two main issues, which would be very appreciated if someone could help me with:

1. When SOURCEGRANDAVERAGING, "ERROR: the input sources vary in the field inside". Below this message you can see the code I am using.

  Should I make additional normalization prior to / in the creation of the individual grid? 
  I found this link which is specific to Neuromag data but it says is outdated (?). 

  Or should I interpolate the source estimation to the template, instead of to the individual-mri?
  When doing so (without after normalizing it), everything works fine but my plots looks like attached (grandavg of 7 subjects). 

2. When creating a SPATIAL COMMON FILTER for comparing the Post stimulus sources of two conditions (effects were baseline corrected within condition in sensor space), 
  should the Allappended input data include the Post-stimulus and Pre-stimulus intervals of each condition (e.g. PrestimA + PrestimB + PoststimA + PoststimB)?

Any comment would be very helpful! 

Thank you in advance, 

All the best,



    %% Interpolation, normalization and grandaverage
    load source mri_real template

    source.pos=template_grid.pos; % right(?) 
    cfg              = [];
    cfg.downsample   = 2;
    cfg.parameter    = 'pow';
    sourceInt        = ft_sourceinterpolate(cfg, source, mri_real);  
    cfg = [];
    cfg.spmversion   = 'spm8';
    %cfg.template    = '~/fieldtrip/external/spm8/templates/T1.nii'; 
                               % When enabling this parameter i get this error: "the head coordinate system of the template does not seem to be correspond with the mni/spm convention".
                               % However should be one taken by default and unablinginn it works fine so it is confussing (?)
    sourceIntNorm    = ft_volumenormalise(cfg, sourceInt);
    %% grand average for 7 subjects

    cfg.parameter    = 'pow';
    [grandavg]       = ft_sourcegrandaverage(cfg, sourceIntNorm{:});


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