Hi All,
Can anyone tell me how SPM implements multiple masks? I've tried two
methods which I'm told should produce equivalent results:
The first method is to select the main contrast, then select three
other contrasts as masks in the spm GUI (by ctrl+clicking), and
exclusively masking them at p=0.05
The second method has been to use imcalc to create one big exclusive
mask using the formula:
i1.*((i2<threshold)&(i3<threshold)&(i4<threshold))
with the two-tailed t-threshold of 2.04 (df=31, so p=0.05)
Then to use this big mask to exclusively mask the main contrast
These two methods actually give slightly different answers - slightly
different cluster locations (some identical, some similar), cluster
sizes approx 20% bigger for method 1.
Which method would you go with?
Best wishes,
Matthew
--
Dr Matthew Whalley
Research Fellow
Department of Psychology
University College London
WC1E 6BT
Tel: 020 7679 5365
Email: [log in to unmask]
|