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A regressor is defined as a column in your design matrix. Even if you didn't add a "regressor" when you created the model, specifying events and PMs will create regressors. In your experiment, you should have a design matrix with 3 regressors/columns: (1) Task Effect (task convolved with HRF) (2) PM for the task (task*behavioral modulator convolved with HRF) (3) Constant term. If you don't have 3 columns, then there is more to your experiment and more information is needed. The rules for generating contrasts is as follows and are generalizable to any design. Now, start with the null hypothesis, then build the contrast from there. Ho: Task>0 Task=0 Find the columns for the task, assign it a weight of 1, all other columns 0. This is based on the coefficients of the equation generated from the null hypothesis. CONTRAST: [1 0 0] Ho: PM>0 PM=0 Find the columns for the PM, assign it a weight of 1, all other columns 0. This is based on the coefficients of the equation generated from the null hypothesis. CONTRAST: [0 1 0] 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, Jun 5, 2015 at 7:08 AM, Joelle Zimmermann < [log in to unmask]> wrote: > Hi, > > This is my first time running an SPM analysis, so I would really > appreciate if anyone is willing to offer some step-by-step guidance. > > I'm doing a first-level fMRI analysis. I have 10 trials each of 62 TR, > with 7 TR rest in between. > > I've defined a single condition, with 10 onsets. I've also defined one PM, > where I inputted my behavioural data (the idea is that activation would > reflect behaviour). > > Now I've created the fMRI model specification, I've gone through the > Estimate step, here I choose a "Classical" model. Now, I click on the > "Results" button, and I am prompted to choose my SPM.mat. > > Then, I am taken to the SPM contrast manager, where I have to define a new > contrast. I understand that a contrast is defined by putting 1's and 0's - > one number of each individual regressor you have. However, I didnt actually > input any 'Regressors'. I only input one 'Parametric Modulator'. > > Does anyone have any suggestions of how to define a contrast in my case? > Thanks, > Joelle >