This may reflect my abysmal ignorance of statistics, but I am stuck and
confused.
When I run a group analysis on a certain dataset with no prethreshold
masking, and cluster correction at p<0.05, I observe widespread
clusters of positive Z's, including in the amygdalae. If I use a
prethreshold mask on several cortical areas and the amydalae (and I
have confirmed the the amygdalar portion of the mask includes the +Z
clusters in the unmasked results), the amygdalar clusters do not
appear. If, however, I use a mask which ONLY includes the amygdalar
portions of the previous mask, the clusters do appear.
I thought that using a mask would make the cluster correction less
stringent, and so I am confused as to why the amygdalar clusters would
show up in the unmasked image, not in the large masked image, but would
show up in the amydalar masked image. Have I completely misunderstood
cluster correction?
I have checked, and all other aspects of the analysis were identical.
The mask images are 0 outside the mask and 255 within the mask.
Thanks in advance.
Richard Albistegui-DuBois, Ph.D.
UCLA Brain Mapping/Neuropsychiatric Institute
phone: (310) 825-3814
email: [log in to unmask]
AIM: dubistegui
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