[FieldTrip] between-groups cluster stats

Nuria DoƱamayor Alonso nuria.donamayor at neuro.uni-luebeck.de
Wed May 16 13:49:15 CEST 2012

Dear fieldtrip users,
I am currently analyzing data from a between-groups study and I am having some trouble programming the stats... Data are from a neuromag 306 system and I am using grand averages (keepindividual = yes) of the combined planar gradiometer data. I have followed the fieldtrip tutorial on cluster-based permutation tests on ERFs, so my script currently looks like this:

cfg = [];
cfg.latency = [0 .5];
cfg.method = 'montecarlo';
cfg.statistic = 'indepsamplesT';
cfg.correctm = 'cluster';
cfg.clusteralpha = 0.05;        
cfg.clusterstatistic = 'maxsum';    
cfg.minnbchan = 3;                 
cfg.neighbours = neighbours;
cfg.tail = 0;                   
cfg.clustertail = 0;
cfg.numrandomization = 500;

design = zeros(1,(size(g1.individual,1)+size(g2.individual,1)));
design(1,1:size(g1.individual,1)) = 1;
design(1,(size(g1.individual,1)+1):(size(g1.individual,1)+size(g2.individual,1))) = 2;

cfg.design = design;
cfg.ivar  = 1;

[stat] = ft_timelockstatistics(cfg, g1, g2);

Still, though the script works, creates one or two clusters and produces no error, the output makes no sense. For example, there is a pretty huge difference in the ERFs between around 50-150 ms, but the output only shows a couple of sensors forming a cluster at 32 ms. Up to now, I had just performed within-subjects stats, so I guess there is probably something wrong in my design... I would be very thankful to any help!

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