Hi All,
I've got some thresholding questions:
1. For cluster based thresholding, is the thresholding applied to resel-corrected data or
uncorrected data? It wasn't clear to me from the manual if cluster- and resel-based corrections
are mutually exclusive.
2. For estimating number of resels, does feat estimate smoothness only from the size of the
spatial filter or does it also try to estimate the smoothness in the pre-filtered data?
3. I have consistently come across the following situation: I do a third level analysis (Z
thresh=2.3, clust P thresh=0.01). There is no activation after thresholding. When I look at the
zstat map and threshold at Z=2.3, I get large blobs (for instance, I'm looking at one such blob that
is approximately 5cm x 2cm x 3cm). So, obviously the clustering, at P thresh=0.01, is eliminating
large areas of activation.
But the thing that I find really puzzling is the unthresholded zstat map itself. If I set the color look
up table to render3, I get very meaningful patterns of "activation". For example, I get no activation
to an auditory stimulus when I use the default thresholding, but when I look at the render3 zstat
map, I get the whole superior temporal gyrus turning bright red. My point is that by looking at the
raw zstats, one can easily identify the auditory cortex despite having no significant activation after
thresholding. Any comments on this scenario? Will histogram mixture modeling eliminate these
"false negatives"?
many thanks,
jack
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