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Your contrasts are correct. It shows the effect of time; however, I'm not sure the you eliminate the issues that occur in the task event contrasts. For example, what if the task-default switch or visual activation changes over time, then the time effect is not the pure effect of the task. 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 Tue, Dec 3, 2013 at 3:32 PM, Colin Hawco <[log in to unmask]> wrote: > Hi all, > > I am working on an analysis for a study design on 'effort'. We are > hypothesizing that neural activity related to effort will increase over > time for our 'effort' events. > > I am attempting to model this using parametric modulators, which I believe > is the correct approach. But I have no direct experience using parametric > modulators and thus would prefer to check my work with the list before > showing results to co-authors. > > We have 6 sessions per person. I am not interested in session x effort > interactions at this time (due to the nature of the experiment), but wish > to identify voxels where the neural activity to our effort events increases > over time. So, I added a 1-st order time modulation. We actually have 2 > event types, and I added a modulator for each, and ran the GLM using an HRF > only model for now. > > So my design matrix has 4 columns per run [type1, type1*time, type2, > type2*time]. > > if I want to find voxels where activity increases over time for event > type2, can I just run a contrast of 0 0 0 1? I think this is explicitly > effect of time after removing task effects, and thus doesn't have the sort > of issues (task-default switch, visual activation, etc.) with a main > effects contrast of a task event (like 1 0 0 0). > > Any advice and/or confirmation that I am on the right track would be > appreciated. > > Thanks. > Colin >