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Hi Nebl, Thanks for your help. I think I am starting to understand! Yes, I think I have 3 regressors as you suggest! So now to set up the contrast in the SPM contrast manager. Do I understand correctly that I test the effect of each regressor separately? First, by putting in a T contrast [1 0 0], I test only the effect of ONLY my first regressor, the task activation (versus rest). (I attach the output figure, I guess the shaded regions show voxels where task is significantly different from rest?) Then, by putting in a T contrast [0 1 0], I test for the effect of ONLY my second regressor, the behavioural parametric modulator. If I were interested to test both first (task activation) and second (behaviour PM) together, how can I do this? Something like [1 1 0]? Forward the corresponding con images (stored in the individual analysis folders) into a one-sample t-test for group statistics. Do you mean after having done the first-level analysis, to forward the con images into a 1 sample t-test for the second-level (group) analysis? How can I do this.. do I forward after starting the second-level analysis, or in the first? Within the group models you would either set up an (undirected) F contrast [1], showing voxels associated with a significant effect, or go with T contrasts. As T contrasts within SPM are one-sided you would go with two contrasts within the group model, [1] showing positive task activations (or positive linear relationship wih the PM = increasing activations with increasing PM values) and [-1] for negative task activations (or negative linear relationships). Here you also refer to the second-level group analysis right? Thanks, Joelle On Fri, Jun 5, 2015 at 2:29 PM, H. Nebl <[log in to unmask]> wrote: > Dear Joelle, > > No, the design matrices are created before the analysis. For "condition > regressors" stimulus function matrices (stimulus on/off) are constructed > based on onsets, durations, which are then convolved with e.g. the > canonical HRF, resulting in the different predictors, which are then used > in the GLM. In your case you probably have two regressors reflecting the > task and the PM, one constant and possibly some additional regressors > corresponding to the motion parameters (to explain some of the remaining > variance due to head motion). From a statistical point of view there's no > difference between "condition regressors", "PM regressors", or > "regressors", it's just different ways how they are constructed. > > For "task activation" you would set up a T contrast [1 0 ... ] on > single-subject level with ... indicating zero-padding the rest of the > columns. Forward the corresponding con images (stored in the individual > analyis folders) into a one-sample t-test for group statistics. Same for > linearly modulated activations based on the behavioral data, the PM should > be represented by the 2nd row in your design matrix, thus you would go with > [0 1 ... ]. Within the group models you would either set up an (undirected) > F contrast [1], showing voxels associated with a significant effect, or go > with T contrasts. As T contrasts within SPM are one-sided you would go with > two contrasts within the group model, [1] showing positive task activations > (or positive linear relationship wih the PM = increasing activations with > increasing PM values) and [-1] for negative task activations (or negative > linear relationships). > > The SPM manual also has several chapters on how to set up single-subject > and group models based on some example data sets, which can be retrieved > from http://www.fil.ion.ucl.ac.uk/spm/data/. > > Best > > Helmut >