Hi Mark,
you can extract the time course separately for each session and also create
the PPI terms independently. However, when actually run the PPI analysis
enter the PPI terms from each as separate sessions again. If you are then
interested in the mean effect of the interaction term across all session,
you would have to weight all interaction regressors with a "1". The
resulting single-subject con-images can then be tested in a 2nd level analysis.
Cheers,
Jan
Mark Eldaief wrote:
> Hi SPMers,
>
> We have a very simple, technical SPM5 question with respect to VOI
> extraction for PPI analysis.
>
> When we want to extract a VOI from every subject on the 1st level
> (fixed effects), it requests to choose session 1, 2, 3 OR 4 (since
> four sessions were modeled) but of course we would like to extract the
> adjusted time-series throughout the ENTIRE experiment (e.g. all four
> sessions). Is there anything we can type in there so it allows us to extract an
> adjusted VOI from all 4 sessions at a time (we tried entering 1:4, 1234 and
> 1,2,3,4 but it keeps saying "scalar required")? If this is not possible, do we
> have to extract VOIs separetely for all 4 runs and combine them somehow
> afterwards for the new PPI first level? If so, how is this done?
>
> Thanks a lot for your help, it is much appreciated!!
>
> Mark
>
--
Jan Gläscher, Ph.D. Div. Humanities & Social Sciences
+1 (626) 395-3898 (office) Caltech, Broad Center, M/C 114-96
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