Dear Fatima:
At 03:09 PM 5/2/2005, FATIMA HUSAIN wrote:
>Hello,
>
>-----------------------------
>I have a block design with two tasks (Task1 and Task2), and rest as baseline
>(implicitly modeled).
>In the past I have done PPI of Task1 - Task2, with the task vector being
>(1 -1)
>Now I want to do a PPI of Task1-Rest.
>
>Should I multiply with the contrast (1 0) for (Task1 Task2) resulting in
>Task1 - Rest? Would SPM group Task2 with Rest or take it out completely?
I don't think this would work for the reason you mention below. You're not
calculating Task1 - Rest but Task1 implicitly versus Rest+Task2, since you
would be setting the Task1 weight to 1 and the weight for Task2 to 0 (rest
is implicitly 0).
>Or do I need to go back and model Rest as Task3 and use the contrasts (1 0
>-1 )for (Task1 Task2 Task3/Rest) ?
Yes if you want to directly compare Task1 - Rest.
Darren
>Thanks in advance,
>
>Fatima T. Husain, Ph.D.
>NIDCD/NIH
>Bldg. 10/ Room 6C-420
>Phone: 301-594-7758
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Darren R. Gitelman, M.D.
Cognitive Neurology and Alzheimer¹s Disease Center
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
Voice: (312) 908-9023 Fax: (312) 908-8789
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