Hello SPMers:
I defined a contrast among two conditions and I got some areas of differential
activation. Then, I did the same contrast but based on an exclusive mask first,
and second, an inclusive mask. The mask was the result of the conjunction (no
global) of the two conditions contrasted afterwards at a p<0.001
(random-effects analysis) for inclusive and exclusive masks (I am talk about
inclusive and exclusive masks as two different masks that come from the same
contrast). The results after masking are mostly the same compared to the direct
contrast without inclusive/exclusive masking but:
1. There is a reduction on the extension of the differences among conditions
when masking. Why?
2. Some areas of differential activation when we did the direct contrast among
conditions did not arise when masking. Specially those closer to the boundaries
among masks. Why?
When I visualized the exclusive and inclusive masks from the conjunction
contrast, the exclusive mask boundary is not exactly limited to those areas out
from the inclusive mask. Therefore, what should I undertand by exclusive mask?
Finally, is there any paper or webpage that explain conjunction at RFX level? It
seems to have a more descriptive value, though at FFX has an inferential value.
Thanking you in advance for any advice.
Alfonso.
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