[HELP] Clusterplot not highlighting clusters

[Manish Saggar]

All,

Any help is appreciated. Please let me know if I am doing any mistake.

Original email is below.

Regards,
Manish

On Wed, Sep 9, 2009 at 11:56 AM, Manish Saggar <manish.saggar at gmail.com> wrote:
> Dear All,
>
> I am a novice user of FieldTrip and I love the tools provided by you
> guys. Great work.
>
> I have a question, regarding the analysis I recently did. Any help is
> appreciated. I am confused why the cluster is not mapped on the areas
> that visually show clear reduction.
>
> I am comparing two conditions (with-in subjects) using depSamplesT
> statistic. Both of the conditions are 1 min of EEG data and I
> calculate powerspectrum over those 1 min windows using segment of 1
> second windows with 50% overlap. Condition are named as pre and post.
>
> I have attached topoplotER of power spectrum for each condition in
> alpha band (8-12Hz). Clearly in post there is reduced power in left
> (mainly) and right hemispheres at the back of the head as compared to
> pre. However in the clusterplot (raweffect) the cluster is mainly
> situated in midline frontal and parietal areas. Actually it is quite a
> large cluster, covering almost all channels. The thing that worries me
> is that it just didn't cover the the channels which clearly shows
> difference by visual inspection between two conditions.
> Also shouldn't the cluster be located only (or mainly) where the
> difference can be seen in pre and post topoplots.
>
> For convenience I have plotted all plots with same zlim.
>
> Here is the code that I used for running stats:
> -------
>        cfg = [];
>        cfg.channel          = {'all'};
>        cfg.latency          = 'all';
>        cfg.frequency        = foi;
>        cfg.method           = 'montecarlo';
>        cfg.statistic        = depsamplesT;
>        cfg.correctm         = 'cluster';
>        cfg.clusteralpha     = 0.05;
>        cfg.clusterstatistic = 'maxsum';
>        cfg.minnbchan        = 2;   %works best.
>        cfg.tail             = 0;
>        cfg.clustertail      = 0;
>        cfg.alpha            = 0.025;
>        cfg.numrandomization = 1000;
>
>        subj = 28;
>
>        design = zeros(2,2*subj);
>        for i = 1:1:subj
>           design(1,i) = i;
>           design(1,subj+i) = i;
>        end
>        design(2,1:subj) = 1;
>        design(2,subj+1:2*subj) = 2;
>        cfg.design = design;
>        cfg.uvar = 1;
>        cfg.ivar = 2;
>        cfg.layout = 'ng.sfp';
>        cfg.neighbourdist = 0.1; % this gives the neighbor count on
> average to 3.2
>        cfg.avgoverfreq = 'yes';
>        stat{win} = freqstatistics(cfg, post, pre);
> ----------
>
> Regards,
> Manish
>

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