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Hi SPM community, Guillaume, Donald this is a test set up question following up on previous responses. Assume the following experiment design: block, one task, 2 sessions, 12 participants, one custom regressor (R) that models the changing stimulus intensity of the task. First level Analysis: I have the following questions: (1) Is there task related activity? I am setting this up as shown in the attached diagram with a '1' for the task and all zeros for the rest of the parameters. (2) Does the addition of the custom regressor (R) change my activation? That's a more tricky question and I am not quite sure about it. Should I set that one up as a '1 1 followed by zeros' - contrast or a '0 1 followed by zeros' - contrast? Alternatively, should I run 2 models, one including the custom regressor 'R' and one without it and I am getting two .mat files in my 1st level analysis, how do I then set up my model comparison in SPM? I understand that comparing nested models would be an F- test, but how do I enter two .mat files in the contrast manager? (3) If I figured out the proper way at the subject (1st) level, how do I use this information at the second level. Presumably, this depends on the approach at the first level. Thanks for you help and I hope this will be of interest two others. Michael