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The correct F-contrast fro the main effect of time would be: [1/2 -1/2 0 1/2 -1/2 0 zeros(1,15); 0 1/2 -1/2 0 1/2 -1/2 zeros(1,15)] This will test if any of the time points are different from each other. The "main effect" of time in group A1: [1 -1 0 0 0 0 zeros(1,15); 0 1 -1 0 0 0 zeros(1,15)] This will test if any of the time points are different from each other in group A1. If you want a decrease over time in group A1, then use a T-test to get direction: [1 0 -1 0 0 0 zeros(1,15)] This contrast only requires that B3<B1, which would make a negative slope irrespective of B2. If you want a decrease from B1 to B2 and B2 to B3, then you need multiple contrasts and to combine them after thresholding. Hope this helps. Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Postdoctoral Research Fellow, GRECC, Bedford VA Website: http://www.martinos.org/~mclaren Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. On Fri, Aug 8, 2014 at 4:20 AM, Robert Schulz <[log in to unmask]> wrote: > Dear SPMers, > > for 2nd level analysis, I set up a 2x3 flexible factor design, including > the interaction terms between the within-factors A and B = A1B1 A1B2 A1B3 > A2B1 A2B2 A2B3 and the subject terms (between) according to page 6 in the > paper of Gläscher/Gitelman: > > Design matrix = [ A1B1 A1B2 A1B3 A2B1 A2B2 A2B3 + 15 subject terms ] > > I wonder whether the F contrast > > 1 0 -1 > 1 -1 0 > 0 1 -1 > > would answer the question in which voxel we observe a decrease of > activation over time across the 3 time points (factor B) in condition A1? > > I would be very grateful if anybody could help me with this. > > Thank you very much. > Best wishes, Robert >