Thank you for your answer.
I have a question about this part.

> If you are working in Talairach space, consider creating a
> mask from the TT_N27+tlrc dataset (resampled to match yours).

Then, how to make the mask file?
The command is
3dAutomask -dilate 1 -prefix "something" TT_N27+tlrc
or 3dAutomask -dilate 1 -prefix "something" "my functional file+tlrc"

And, is it OK to make one participant's mask file when I do the group analysis.
My understanding is just like that:
1) I will make one subject's mask file.
2) All subjects' data are transformed into Talairach. So, the mask space will be same.
3) I don't have to sum individuals' mask files. I can just use one participant's mask file as a mask for AlphaSim.

Am I correct?

Woogul Lee