Dear Spm'ers,
I have just a little question concerning the design of a fMRI-study.
We have four conditions (A,A',B,B') which are examined in one session per
condition with alternating on/off epochs, 4 rest/avtivation cycles per session,
40 sec per epoch.
We are interested in the differences between A / A' and B / B'.
I am pretty new to the field, so I am not 100% sure about how to define the
correct contrasts for those questions.
I want to define one big design matrix consisting of all four conditions by
modelling the boxcar-function convolved with the hrf for every single condition.
My understanding is that (1 -1 0 0) and (0 0 1 -1) would answer the question
about the differences.
Is this correct ?
And if so, what is the difference to (-1 1 0 0) and (0 0 -1 1), respectively ?
Any suggestions and comments would be greatly appreciated, since I am just
starting off working with SPM.
Thanks in advance,
Tobias Flaisch
Dep. of Psychology
University of Konstanz
78460 Konstanz
Germany
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