issues with clusterrandanalysis

Eric Maris maris at NICI.RU.NL
Mon Apr 9 12:11:07 CEST 2007

Dear Andre,

> I am beginning to use the clusterrandanalysis function, but have not been
> finding any significant clusters in my EEG data. I changed alpha and
> alphathresh to be 0.5, but this still didn't produce any results
> (posclusters and negclusters are both empty). To test whether the config
> settings were actually working, I generated some random time frequency
> using the following commands:
> s = size(TFR.powspctrm (s is 17 trials by 64 channels by 40 freqs by 99
> steps)
> rpow = rand(s); (produces pseudorandom nums between 0 and 1)
> TFR.powspctrm = rpow;
> I reran clusterrandanalysis with this new TFR, but still got no clusters.
> This puzzles me, because a random series of numbers should be
> different from physiologically produced spectral data.

My first guess is that there is something wrong with your neighborhood
structure. Can you send me a copy of the screen output (only the part before
the counting of the randomizations)?

When using MEG-data coming from a  CTF system, this neighborhood structure
is calculated automatically. However, I guess you are using a different
sensor configuration. In that case, you have to supply this information to
clusterrandanalysis. You can find more information about this in the online
help of clusterrandanalysis.

Kind regards,


> I used the basic config settings found in the tutorial, which were:
>   cfg.statistic = 'indepsamplesT';
>   cfg.alphathresh = 0.5;
>   cfg.makeclusters = 'yes';
>   cfg.minnbchan = 2;
>   cfg.clusterteststat = 'maxsum';
>   cfg.onetwo = 'twosided';
>   cfg.alpha = 0.5;
>   cfg.nranddraws = 100;
> = 'all';
>   [clusrand] = clusterrandanalysis(cfg, TFR1, TFR2);
> Any ideas what I am doing wrong?

More information about the fieldtrip mailing list