[FieldTrip] Testing ITC differences using diff_itc in a first and second level analysis

[Nicolas Farrugia]

Dear all, 

I m trying to analyse differences in Inter-Trial Coherence between conditions in a group of subjects. I figured out with this paper "Nonparametric statistical testing of coherence differences" by Maris, Schoffelen & Fries 2007, that this can be done reliably using non-parametric tests with Montecarlo permutations and it s implemented in Fieldtrip under the statfun diff_itc in the montecarlo method.
I m now using the cluster based  tests in Fieldtrip on my complex TF data using the following parameters (I extracted only the relevant ones for the discussion) : 

cfg.method           = 'montecarlo';
cfg.correctm         = 'cluster';
cfg.clusteralpha     = 0.05;
cfg.clusterstatistic = 'maxsum';
cfg.minnbchan        = 2;
cfg.tail             = 0;
cfg.clustertail      = 0;
cfg.alpha            = 0.025;
cfg.numrandomization = 500;

cfg.statistic = 'diff_itc'; 
cfg.complex = 'absdiff'; 
cfg.parameter = 'fourierspctrm';
cfg.avgoverfreq = 'yes';

This also need a clustercritval : so my first question will be : 

-> How to choose the clustercritval in the case of this test of ITC differences ? 

I ve been trying different things but I m not sure. 

Then, this constitutes my first level analysis, so for each subject I have cluster statistics, their time/spatial course and their significance.
>From here how can I go towards for a second level analysis ( similarly as in SPM) ?  Is there already building blocks for that in Fieldtrip ? Should one try to find a cluster center / time window and use the cluster statistics, and use the resulting values from all subjects in a non-parametric test ? 

Thanks for your help,

Nicolas

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Dr. Nicolas Farrugia
Post-doc 

Research Group "Subcortical contributions to comprehension" 
Department of Neuropsychology
Max Planck Institute for Human Cognitive and Brain Sciences 
Stephanstraße 1A, 04103 Leipzig, Germany 
Phone : +49 (0) 176 848 90 393

http://nicolasfarrugia.fr