I posted a message on the statistical analysis a little while back, but no
one answered. So I’ll try to condense and ask more specific questions.
I performed the first-level analysis two ways on a block design task, 4
epochs of 24 seconds each interspersed between 5 epochs of 30 seconds each,
with a TR of 3 seconds, for a total of 82 measurements/volumes.
First, I performed the analysis without the motion correction parameters
giving me a total of exactly two of those beta hdr/img pairs.
Then I included the motion parameters from the Realign step. That gave me a
total of 8 beta_xxxx.hdr/img” files. There are 6 motion parameters. Along
with the condition I defined, that gives a total of 7.
Is the last parameter the error? One beta for the condition, one beta for
every motion correction parameter, and one for the error. That would make sense.
Secondly, I set the units for design to “seconds” instead of the default
“scans”. I defined the condition in seconds, but the motion parameters are
in scans. There are 82 rows. When I add the rp_*.txt file to the “multiple
regressors” field of the “Subject/Session” added to the “Data & Design”
portion, does it automatically assume that it is in scans? Will this mess my
analysis up? If not, what can I do to convert it to seconds? Because it
would be easier for future when I convert everything to seconds.
Finally, I am very confused regarding the 2nd level analysis. Assuming each
beta is for one condition, if I had the betas of several control subjects
and patients for the same condition, I want to get the group activation maps
for both the patients and the controls. And I also want to find the
differences in the activation between the two groups. What do I use for
that? One-sample t-test, 2-sample t-test, paired t-test, multiple regression
or flexible factorial? When would I use each design in the 2nd level
analysis? I want to do random effects analysis. I’ll appreciate any help.
Thanks.
- Ananth
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