Thanks for the info. And yes - I meant that AFNI does per-voxel time series normalization, not normalizing all voxels. Most psychophysiological measures (e.g. ERPs, electrodermal, cardiac, etc.) use a baseline immediately preceding stimulus onset to control for things like local drift, habituation, etc even if changes are not huge. Even with what you have said here, it makes sense to me to use a local baseline for the same reason with fMRI. Most physiological systems will recover with 5-20 s, which is a typical inter-trial interval in BOLD studies. Having analyzed the same data both ways with little difference, I guess it would be safe to say one could use the local baseline, right? thanks, mb
