Dear SPM experts
I have a rather basic question on comparing two sessions with paired
t-tests. I have an event-related fMRI design with two sessions that use the
same types of stimuli but different instructions. Now I want to assess the
effect of the instruction by comparing (relevantstimulus1 -
controlstimulus1) versus (relevantstimulus2 - controlstimulus2). On a first
level, I have fitted models for each session separately. Now I want to
compare the resulting contrasts on a second level by paired t-tests.
First, I wonder whether this is correct, because
secondly, when I try to do so, I get a separate predictor for each pair of
scans. Now when I set all predictors to 1 (except constants), SPM gives an
error message.
Where am I wrong?
Thank you for your input
Dominik R Bach
University Hospital of Psychiatry
Berne, Switzerland
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