issues with clusterrandanalysis

[Andre Bastos]

Dear Fieldtrippers,

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.

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?

Thanks,

Andre