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hi all, thanks for the discussion on this issue. in the context of siemens scanners, prospective motion correction is often built into the BOLD sequences these days. would this discussion be applicable in this context as well? i.e. given the automatic slice reconfiguration, would the ratio of motion to slice timing related error be much closer? also, jesper and mark, where are you getting the numbers from relating voxel displacement to signal change? In summary, it is a messy, complicated issue and the existing methods are > not perfect (a 4D interpolation would be better). > a 4d registration algorithm actually exists that can handle slice timing + motion correction in one step. Roche A. A four-dimensional registration algorithm with application to joint correction of motion and slice timing in fMRI. IEEE Trans Med Imaging. 2011 Aug;30(8):1546-54. http://dx.doi.org/10.1109/TMI.2011.2131152 and is available in the NiPy package: nipy.org/nipy/stable/api/generated/nipy.algorithms.registration.groupwise_registration.html#fmrirealign4d and wrapped for NiPype: nipy.org/nipype/interfaces/generated/nipype.interfaces.nipy.preprocess.html#fmrirealign4d cheers, satra