Dear Glad
Masking is just that: It just doesn't show those voxels that are not in your mask images (exclusive mask) / just shows voxels within your mask image (inclusive mask) [look at spm_getSPM at about line 600]. The statistics, more precisely the correction for multiple comparisons), however, still runs with respect to the initial analysis space.
Smal volume correction, in contrast, only corrects for the smaller search volume and provides correcte p-values for this new analysis space. It doesn't however, update the image you see in the glass-brain.
So it is actually a good idea to combine both, mask out voxels outside the mask (for dispay) and then re-compute your corrected statistics using SVC for the same mask.
Best
Simon
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Von: SPM (Statistical Parametric Mapping) [[log in to unmask]]" im Auftrag von "Glad Mihai [[log in to unmask]]
Gesendet: Montag, 14. Mai 2012 10:46
An: [log in to unmask]
Betreff: [SPM] Difference between mask with image and small volume
Hi,
can someone explain to me the difference in calculation between masking
(apply masking) a contrast with an image (let's say an anatomical ROI),
and a small volume correction?
Regards,
Glad
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