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Dear SPM community, i'm a little puzzled on the order of processing time series fMRI data for a multi-subject random effect analysis. We scanned several hundreds functional images of 4x4x4mm voxel size per subject, and coregistered them with each subjects T1. So far so good. There are several options to achieve normalized contrast images per subject, for a random effect analysis: 1. normalize all functional images using the subjects T1 to the T1 MNI template brain, which by default changes the resolution of the normalized time series to the template's resolution, 2x2x2. Estimate your model, calculate contrast images, and use those for a random effect comparison. 2. same as above, but now changing the resolution of the normalized functional images to 4x4x4 (by using the default-edit option), as they were actually measured. The time necessary to complete the calculations as well as required disk space is reduced by a factor of 8. 3. Estimate your model on un-normalized (but of course coregistered and realigned) time series. Calculate contrast images, determine normalization parameters from the T1 image, and apply them to the contrast images. Finally, do a random effects analysis on the normalized contrast images. There seems to be some kind of consensus on option 1. I do not see much reasons, however, why the time-series resolution has to be better than 4x4x4, which has in our case been measured. The only reason i can think of is that voxels get displaces by normalisation less than 4x4x4, and significant voxels that previously (before normalization) were aligned, are now slightly misaligned. Analysis might then perhaps benefit from smaller voxels? Just a feeling ... Another worry is that decreasing voxel size below the actually measured resolution, increases the number of comparisons one makes, and the statistics more conservative. Does anyone have any ideas or even references on this topic? I do know how te change voxel sizes in the defaults batch-script or menu, it's merely a theoretical question. any help is very much appreciated! Cheers, Bas -------------------------------------------- Dr. S.F.W. Neggers dept. of Psychonomics,Helmholtz Institute Utrecht University Heidelberglaan 2 3584 CS, Utrecht, the Netherlands Tel: (+31) 30 253 4582 Fax: (+31) 30 253 4511 E-mail: [log in to unmask] Web: http://www.fss.uu.nl/psn/pionier --------------------------------------------