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| In the framework of spm99, is there any sense in which movement between | sessions is more benign than movement within a session? (I assume a | session is a time-contiguous set of scans; thus, one could have many | "sessions" in one afternoon at the scanner.) For example, if I decide I | don't like movement more than (say) 1mm/1 degree within a session, should I | extend this judgement to between sessions? It all depends how correlated the movement is with the effects of interest modelled by the design matrix. If you are not looking for interractions between sessions, then movement between sessions should not be a problem. This is especially the case if the different sessions are modelled in the same way as different subjects would be. Best regards, -John %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%