clusterrand electrode neighbours

Eric Maris maris at NICI.RU.NL
Thu May 25 21:09:11 CEST 2006

Hi Stephan,

> After applying clusterrandanalysis I get several significant clusters in
> the
> same time-frequency range in neighbouring electrodes, i.e. one cluster for
> each electrode in that range. I assumed that they should be collected to
> one
> one cluster if the effect is in the same range and region?

Two (channel,time,frequency)-triplets with the same time and frequency
values and neighbouring electrodes must belong to the same cluster (if their
T-statistics exceed cfg.alphathresh, of course).

> Here is what I tried:
> elec = read_fcdc_elec('27mtg.sfp');       % the exported BESA coordinates
> cfg=[];
> cfg.statistic  = 'depsamplesT';
> cfg.alphathresh = 0.05;
> cfg.makeclusters = 'yes';
> cfg.clusterteststat = 'maxsum';
> cfg.onetwo = 'twosided';
> cfg.alpha = 0.05;
> cfg.nranddraws = 1000;
> = 'all';
> cfg.neighbourdist = 0.04;           % I also tried 0.05 with the same
> result
> cfg.latency = 'all';
> cfg.elec   = elec;
> [stat] = clusterrandanalysis(cfg,fileB,fileA);
> I also tried the analysis with manually defined neighbours, but received
> the
> same result.
> I attached the elec variable with the coordinates.

I did not find the elec variable in the attachment. What is the dimension of
the BESA coordinates? Is it centimeters? In that case,
cfg.neighbourdist=0.04 is so small that no electrode will be selected as a
neighbour. You could calculate the inter-electrode distances on the basis of
their coordinates and use that information to determine cfg.neighbourdist.
If that doesn´t help, you can send your cfg and data to maris at I
will have a look at it.


Eric Maris

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