Hi all,
I am interested in modeling linear increases/ decreases in activation over the course of several sessions for a given contrast. I would first like to model linear inc/dec within individual subjects and then take the group mean. Is it correct for my second level to look like this:
EV1 EV2
Subject1 Subject2
Input1 (session1) -1.5 0
Input2(sess 2) -.5 0
(sess3) .5 0
(sess4) 1.5 0
(sess1) 0 -1.5
(sess2) 0 -.5
(sess3) 0 .5
(sess4) 0 1.5
Contrasts EV1 EV2
Sub1 1 0
Sub1 -1 0
Sub2 0 1
Sub2 0 -1
Do I need to orthogonalize the linear trend coefficients w.r.t. “multi-session mean” for each subject or is this unnecessary because the coefficients are already demeaned?
The third level would just be a standard group analysis combined across subjects.
Thank you so much,
Lizz
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