Guys,
I'm going to try another plea for the continuous effect size maps. See
the first graphic on this page for an example:
http://www.mrc-cbu.cam.ac.uk/Imaging/Common/display_slices.shtml
I pasted a reference to a paper making this argument last time, but
just in case anyone has not read it, the argument is very simple.
Let's say you only present a thresholded SPM map for task X, and you
only found area A activated above threshold. You then say: area A is
involved in task X. However, as we all know, just because something
isn't significant, doesn't mean it isn't there. So, the fact that A
_is_ significant, and the rest of the brain isn't, is perfectly
compatible with the whole brain being actually activated, and A being
just above threshold due to noise. So, when we say A is activated by
X, we are really saying, maybe the whole brain is activated by X, and
A got above threshold. We can't even say A is _particulary_
activated by X, unless we test the level of activation in A directly
against the rest of the brain. So, A is activated by X, on its own,
has very little value for localizing function. Therefore, the classic
thresholded SPM has very little value for localizing function.
So, in order to localize function, you need some estimate of what is,
and what is _not_ activated. The simplest way of starting to assess
this, is a continuous map.
The continuous map is also much more useful for meta-analysis.
Any thoughts?
Best,
Matthew
Ref (again):
Jernigan TL, Gamst AC, Fennema-Notestine C, Ostergaard AL. More
"mapping" in brain mapping: statistical comparison of effects. Hum
Brain Mapp. 2003 Jun;19(2):90-5
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