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Tommi > thanks for the clarification! Almost there. However I would like to make > sure of one more thing. Since the "Interaction" button at first level > analysis, according to the manual, merely creates an EV where the paradigm > file 0:s and 1:s for EV1 (stimulus A OFF/ON) are multiplied with those for > EV2 (stimulus B), then the outcome is a paradigm file for the AB stimuli (ie > where A and B are presented simultaneously)? Then, the contrast where the > EV3 (for "Interaction") is set as "1" and everything else as "0" is NOT the > factorial ANOVA interaction we are looking for, rather, it is the stimulus > AB vs REST comparison? No! a [0 0 1] t-contrast is not AB versus rest comparison, it is the positive interaction of A and B (do [0 0 -1] t-contrast to look for a negative interaction). The reason for this is that we are doing multiple regression, EV1 and EV2 model out the effects of A and B respectively alone versus rest - leaving EV3 only representing the AB interaction. Cheers, Mark. Mark Woolrich. Oxford University Centre for Functional MRI of the Brain (FMRIB), John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK. Tel: (+44)1865-222782 Homepage: http://www.fmrib.ox.ac.uk/~woolrich