Dear SPM Experts,
Here is a simple yet interesting question.
When we do SPM result, we usually set p = 0. 001 (uncorrected) or p = 0.05 (FWE correct), then we get the statistical activation mapping and how many voxels activated. My questions is, can we set a specific number of activated voxels (e.g., 1000 voxel totally) and then get the activation map?
The reason to do this is that I have two groups of subjects, young and old, although the final activation map is different between young and old. However, after setting a lower threshold for young subjects, I found the activation maps between the two groups are rather similar. This makes me wonder whether I can actually set a total voxel number and see how much similar the maps of the two group will be. My feeling is that the so-called HAROLD model(Hemispheric asymmetry reduction in older adults) might not be an absolute distinction, but a matter of levels of activations.
It seems SPMS can only set p-level before you can get total activated voxels. Anyone here know about the other way? Thank you very much!
Best wishes,
Gao
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