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Yes, I think a T-contast would highlight voxels with a common task-related response. At the second level, a T-test would constrast whether (common) mean activation is significantly greater than zero. That is, you are testing for task-related similarities in your population. On the other side, a F-test at the second level (as you defined) would test if exist task-related differences in your constrast. As you pointed, a F-contrast give common 'differences' in both directions (positive and negative, or task > control/baseline and control > task). But you can't extent these approximations to F and T tests, because they are different mathematical/statistical tools. If you are new in the matter, just see presentations with experimental fMRI examples to familiarize with it. Hope it helps ;D, Martin 2015-06-15 16:16 GMT+02:00 Joelle Zimmermann < [log in to unmask]>: > Hi Martin, > > Thanks a lot for your input - that's very helpful I didn't know that! So > the F-contrast tests for differences in activations between subjects while > T-contrast with '1' would test for similarities in activations between > subjects? So you think that a T-contrast would highlight voxels where many > subjects show an activation? > > I thought that the F-contrast tests for activation and deactivation > similarities across subjects. But I'm totally new to this and just getting > this from scraping info from various sites. > > Thanks, > Joelle > > > > On Mon, Jun 15, 2015 at 4:03 PM, Martín Martínez <[log in to unmask]> > wrote: > >> Hi Joelle, >> >> in the second level, you have modeled a F-contrast (testing for between >> subjects-related differences). >> If you want to test for common-related activations on constrasts, I think >> you just need to model a T-contrast with a '1'. >> >> Wellcome, >> Martin >> >> 2015-06-15 10:48 GMT+02:00 Joelle Zimmermann < >> [log in to unmask]>: >> >>> Hi - First of all I'd like to thank everyone who has given me great >>> advice on this mailing list - it's really such a helpful resource! >>> >>> Now, to my question. I'm setting up a second-level fMRI analysis in SPM. >>> I've previously done 5 first-level fMRI analysis for 5 individual subjects. >>> I am attaching the results of one subject for viewing (results across >>> subjects are quite similar to this). First-level analysis tested for >>> task-related activations. >>> >>> I now ran a second-level group analysis, forwarding the 5 individual >>> subject con.nii's (ie the con.nii's from the first-level analyses) into the >>> second-level model, specified a one-sample t-test, and set up a simple >>> contrast (an F-test, and just put '1'). However, I didn't get any >>> significant voxels, which I am surprised by, considering all of my >>> first-level single subject analysis look very similar to what I am >>> attaching here. >>> >>> I think there must be something that I am doing wrong. Any pointers >>> would be helpful. >>> >>> Thanks, >>> Joelle >>> >>> >> >