[FieldTrip] Group analysis at source level

[Tyler Grummett]

Hey laura,


Im not 100% sure of what I am about to tell you, as I am not an expert, but I think ft_sourceinterpolate is used in tutorials

to display results on an mri model basically. One such tutorial is:

http://fieldtrip.fcdonders.nl/tutorial/beamformingextended


If you want to be consistent over subjects, I would use a sourcemodel when calculating your source variable, like in:

http://fieldtrip.fcdonders.nl/faq/how_can_i_map_source_locations_between_two_different_representations?s[]=atlas

and: http://fieldtrip.fcdonders.nl/example/create_single-subject_grids_in_individual_head_space_that_are_all_aligned_in_mni_space?s[]=subject&s[]=grid&s[]=mni?


I really hope this helps, it helped me :)


Tyler


*************************

Tyler Grummett ( BBSc, BSc(Hons I))
PhD Candidate
Brain Signals Laboratory
Flinders University
Rm 5A301
Ext 66124
________________________________
From: fieldtrip-bounces at science.ru.nl <fieldtrip-bounces at science.ru.nl> on behalf of Laura Rueda Delgado <Laura.Rueda at faber.kuleuven.be>
Sent: Friday, 25 July 2014 1:06 AM
To: fieldtrip at science.ru.nl
Subject: [FieldTrip] Group analysis at source level

Dear fieldtrip users,

I'm working with source estimations of EEG data. At the moment, I have estimated the sources at the individual level with individual MRIs. I've used ft_sourceinterpolate and ft_volumenormalise to transform the resulting estimation maps into a template for comparison, and I do this for every subject:

 cfg             = [];
    cfg.parameter   = 'avg.pow';
    source  = ft_sourceinterpolate(cfg, source, mri);

    cfg = [];
    cfg.template = '\spm8\templates\T1.nii';
    cfg.parameter = 'all';
    cfg.nonlinear = 'yes';
    cfg.coordsys = 'spm';
    source = ft_volumenormalise(cfg, source);

Once I have the estimated sources for all the subjects, I use ft_sourcestatistics:

cfg             = [];
cfg.dim         = sourcePre_con{1}.dim;
cfg.method      = 'montecarlo';
cfg.statistic   = 'depsamplesT';
cfg.parameter   = 'avg.pow';
cfg.correctm    = 'cluster';
cfg.numrandomization = 'all';
cfg.alpha       = 0.05;
cfg.tail        = 0;
cfg.design(1,:) = [1:num 1:num];
cfg.design(2,:) = [ones(1,num) ones(1,num)*2];
cfg.uvar        = 1;
cfg.ivar        = 2;
stat = ft_sourcestatistics(cfg,sourcePost_con{:},  sourcePre_con{:});

And I get this error:

Reference to non-existent field 'pos'.

Error in statistics_wrapper>get_source_avg (line 643)
  fprintf('only selecting voxels inside the brain for statistics (%.1f%%)\n', 100*length(varargin{1}.inside)/size(varargin{1}.pos,1));

Error in statistics_wrapper (line 206)
    [dat, cfg] = get_source_avg(cfg, varargin{:});

Error in ft_sourcestatistics (line 107)
    [stat, cfg] = statistics_wrapper(cfg, varargin{:});

I check the data structure and the structure of the sources at the individual level, before interpolating and normalising has the pos field, but after these steps, it's gone. How can I work around this error? Do I have to keep the pos field and transform it according to the template?

Thank you in advance for your help.

Best regards,

Laura Rueda
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