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Dear SPMers, I'm a bit confused with how SPM defines brain voxels. I've done a segmentation prior to the statistical analysis, I then perform 16 different amounts of smoothing (0 - 15 mm FWHM) and calculate t-test values for each case. If I calculate the number of t-test values that not are zero, this should in my opinion be constant, i.e. not depend on the amount of smoothing, but it can for example vary from 40 000 for no smoothing to 46 000 for 15 mm smoothing...why is this? /Anders