We've been analyzing some block design data using FEAT, and have encounted a strange negative
bias in the Z and T images generated for our groups by FLAME. We do see a set of positive foci in
plausible locations, but these appear against a background of a consistently negative Z score of
around -5. This would suggest there's either something wrong with our data (but these look ok
from what we can tell) or, more likely, that we are setting up the analysis incorrectly.
I am wondering if this symptom calls to mind any kind of obvious misconfiguration, or if anyone
has advice on how to debug this sort of thing. We did look at the cope images, and these also
appear to have the negative bias in much of the brain.
The design contains three stimulus types (EV's) in non-overlapping blocks, and the problem is
appearing in the general contrast testing for presence of response to all three stim types. The F
images show a global background of abnormally high value, and you can see the zero crossing
separating most of the brain (negative) from the isolated positive foci.
Any advice on how to resolve this would be much appreciated - I can provide all or part of the .fsf
file or output images if needed.
Rick
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