Fellow SPM`ers, another question,
There are a number of more or less old threads on the list
discussing the use of grey matter masks, e.g.
The conclusion I draw from these is that it is not sound to
individualized explicit grey matter masks in the FFX- analyses as it
will cause problems with regards to GFT at the second level. However I
have been reading a number of high- profile articles in which they did
apply grey matter masks (e.g. http://dept.psych.columbia.edu/~kochsner/pdf/Wager_et_al_Reapp_mediation.pdf)
. From my, admittedly limited, reading it seems that the "gold"
standard is to apply a smoothed and thresholded mask based on on the
MNI avg152T1 template, and apply this on in the RFX- analysis.
I have some questions with regards to this approach, however. Wouldn
īt this procedure mess up the analysis with regards to GFT just as
much as applying a mask on the first level?
If this isnīt the case, I canīt help but wonder whether a more sound
approach would be to construct the mask as a mean of the c1 images
that the Unified segmentation procedure produces. Or is the difference
between these two masks post-normalization so small as to be negligible?
Third, provided that it makes sense to use gray matter masks at all,
should the smoothing kernel applied on the mask be identical to the
kernel used on the functional images, or does GFT provide for some
criterion for the smoothness of the mask?
Finally, does the use of a gray matter mask allow one to circumvent
FWE correction to some degree, or at least allow one to use a more
lenient threshold, as it reduces the number of comparisons made?
Thanks in advance,