 |
 |
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 ------------------------------------------------------------------------- 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 -------------------------------------------------------------------------