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Dear Pavel, The cluster-level threshold must take into account not only the total number of voxels in the search volume, but also the cluster-forming threshold and the smoothness of your data. Given the same total number of voxels in the volume, the higher is the cluster forming threshold and the greater is the smoothing the more conservative is your extent threshold. I attached an example of statistical table with different cluster-forming (height) thresholds: Pay attention to height threshold (0.001 and 0.005) and FWEc (24 and 63). Perhaps, the following script can be useful for better understanding of the calculations: http://www-personal.umich.edu/~nichols/JohnsGems5.html#Gem6 Sincerely yours, Vladimir Volodymyr B. Bogdanov, PhD Nutrition and Integrative Neurobiology (NutriNeuro) UMR INRA 1286 - Université Bordeaux 2 UFR Pharmacie 2e Tranche 2e étage Case courrier 34 146 rue Léo Saignat 33076 BORDEAUX Cedex FRANCE >________________________________ > From: Pavel Sokolov <[log in to unmask]> >To: [log in to unmask] >Sent: Monday, October 28, 2013 4:34 AM >Subject: [SPM] Cluster threshold > > > >Hello, experts! > > >Please, help, how can I consider minimum number of voxels in cluster if I need to get overall sum of activated voxels in brain with error. If I right when I don't set extent threshold I can use error = (whole sum of voxels in brain)*p(uncor). > > >Thanks in advance, >Pavel. > >