Dear SPM experts,

After searching the archive I still have 3 questions about SPM's default 
masking threshold.  I apologize if these are naive questions, but I hope 
someone can answer them.

1)  Why is the default masking threshold value set at 0.8 (i.e 
defaults.mask.thresh = 0.8)?  Is there a significance to the value 0.8?

2)  Is there a  down-side to lowering this threshold (other than including 
voxels with low/noisy signal and voxels that are not part of the brain)?

3)  Is there a minimum threshold value that would still yield principled 

Any information would be greatly appreciated.

Stanford Ly
Staff Research Associate I
Department of Psychiatry and Behavioral Sciences
MIND Institute
U.C. Davis Medical Center
2825 50th Street
Sacramento, CA 95817
(916) 703-0298

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