Oliver, The question you raised is fundamentally different from the original post, where they wanted to know how one condition was different from the average of the other two conditions. In your case, the question is where is A>B AND A>C. I would form the two contrasts, threshold them, and then use imcalc to perform the logical AND between the two maps. On Tue, Nov 29, 2011 at 2:36 PM, Olivier Collignon <[log in to unmask]>wrote: > Hi Donald, > There is something I do not get with these contrasts. > Imagine a voxel "x" with parameter estimates of: > Condition A = .5 > Condition B = .5 > Condition C = 0. > > You want to evaluate if this voxel show preferential activity for a > specific condition. > Obviously this voxel do not show a selective preference for task A. > > But if you use the contrast 2 -1 -1, will it give you some "activity" > in this voxel and then wrongly suggest some selective preference for > task A, no ? > Would it not be more adequate to do 1 -1 0 conjonction(and) 1 0 -1 ? > > Thanks, > Olivier. > > > > 2011/11/29 MCLAREN, Donald <[log in to unmask]>: > > For within-subject designs, you should use the flexible factorial design > and > > include a subject term to properly account for subject effects. > > > > The contrasts are correct. > > > > Best Regards, Donald McLaren > > ================= > > D.G. McLaren, Ph.D. > > Postdoctoral Research Fellow, GRECC, Bedford VA > > Research Fellow, Department of Neurology, Massachusetts General Hospital > and > > Harvard Medical School > > 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 Tue, Nov 29, 2011 at 10:22 AM, Marjorie Dole < > [log in to unmask]> > > wrote: > >> > >> Dear SPM users, > >> > >> I have a question concerning second level analysis: > >> > >> I have an experimental design with three conditions, A, B, C, and a > >> baseline. I want to evaluate fMRI activations specifically for each > >> condition versus the two others in my whole group, by testing the > contrasts > >> : A-(B+C), B-(A+C) and C-(A+B). > >> > >> So I did for my first level analysis the following three contrasts: > >> A-baseline, B-baseline and C-baseline. > >> At the second level I used a full factorial design with one factor > >> (Condition; three levels: A, B, C) and then I contrasted each condition > >> versus the two others using the following contrasts : 2 -1 -1 ; -1 2 > -1; > >> -1 -1 2. > >> > >> Is this approach valid? > >> Do you have any suggestion? > >> > >> Thanks for your help, > >> > >> Marjorie > > > > >