Donna:
Thanks for your quick reply (and yes, apparently we've crossed paths on
those "other lists" :-). You have indeed alerted us to some places in the
docs that we missed before. And your additional comments were helpful too.
But needless to say, more questions/comments:
1. Average Area: As I now understand it, this applied to the MFM procedure,
and is the total area above threshold, calculated by sampling the voxel
data (eg: fMRI activation) using each of the 12 B12 surfaces in turn, and
then averaging those 12 totals together. Main use: adjusting thresholds
for the MFM procedure to give results comparable to the AFM procedure. Right?
2. Mid-cortex surfaces, and your FS-related suggestion: Where we use your
provided surfaces to sample (map) the fMRI data, we think we should be
using mid-cortical or pial surfaces, but the surfaces that the tutorial
leads us to appear to be grey/white boundary surfaces. Are we thinking
straight on this, and are there mid-cortical versions of PALS-B12 in
AFNI+tlrc space, for example?
3. "volume-averaged group data": This phrase shows up in a few places, and
we're puzzling over whether it means something different or special
compared to what we *think* it means. Eg: on p67 of Caret_Tutorial_Sep22.pdf:
"Many fMRI studies are analyzed by registering the MRI volumes from
individual subjects to a standard stereotaxic atlas, then carrying out
statistical analyses on the volume-averaged group data."
I think the phrase "carry out statistical analysis on volume-averaged group
data" possibly refers to "voxelwise statistics, using subject variables for
grouping"? Eg: 256x256x256 voxels by 10 subjects go in, 256x256x256
voxels-worth of means, t, z or whatever come out.
Or is there something more to it? If it's a different concept, what is the
"group data" that is being averaged over a volume, and then what is the
statistical analysis that is performed upon it?
Thanks,
Graham
