issues with clusterrandanalysis

[Eric Maris]

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
data
> using the following commands:
>
> s = size(TFR.powspctrm (s is 17 trials by 64 channels by 40 freqs by 99
time
> 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
statistically
> 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,

Eric



>
> 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;
>   cfg.channel = 'all';
>   [clusrand] = clusterrandanalysis(cfg, TFR1, TFR2);
>
> Any ideas what I am doing wrong?