Dear Colline,
of course ... I think your approach is
still valid ...
However, as Mr Will Penny wrote today in
his answer to Peter Clerinx [Another
contrast question], the first level concerns the effect of a condition
‘X’ for
the subject analyzed. As you performed a fix-effect analysis (=1st
level
analysis), your results are only valid for the group studied. Maybe the
reviewer asks you to do a random effect analysis … see http://www.fil.ion.ucl.ac.uk/spm/doc/books/hbf2/pdfs/Ch12.pdf
Similarly, if you have a strong hypothesis,
you
can perform small volume correction (as proposed by Mr Matthew Brett)
or use a
tool dedicated to investigate a region of interest (MarBaR http://marsbar.sourceforge.net/
or
WFU_pickatlas http://www.fmri.wfubmc.edu/download.htm)
Best,
Cyril