Hi Dan and all,
I'm sorry to prolong this already enormous thread, but I'll try to be brief:
Stimulating though this argument has been, I have to disagree strongly
with this:
> I was agreeing that thresholded maps are nearly useless for
> localization, but I don't feel on the whole they're any better or
> worse than unthresholded maps.
I disagree for all the reasons stated elsewhere in the thread, most
recently be Federico. It comes down very simply to the point that Tom
Johnstone made well:
> Without at least a power analysis ... one is really in no position to
> conclude anything at all about brain regions that show no significant
> activation.
I don't think there's any way round this one for the single subject
analysis; the thresholded map is useless for drawing conclusions about
differences between brain areas.
The argument for comparison across studies is simply an extension of
the single subject case; if you have almost no evidence for
localisation in one study, you merely have very little evidence for
localization across 10 studies. If you have the continuous map for
10 studies, and they all show zero or negative activation for area A
and strong activation for area B, you have a much stronger case for "A
is more involved than B" than you could possibly have from 10
thresholded maps, which have simply thrown away this information.
Thanks again,
Matthew
|