Daniel,
I'm curious if you've done any work looking at different threshold values (c1) in 3dDespike. I looked at my clipped 'spikiness' dset where I masked s values <=2.5 and I see that most of the values in the resulting dset are between 2.5 and 3.5. There's only a small percentage of timepoints with values > 3.5. I'm wondering if you could give me some information about why 2.5 was chosen, or is the value of c1 fairly arbitrary as long as we report what we used. In your experience, are 's' values greater than 2.5 typically always artifact of some kind, and thats why 2.5 is the default.

Overall, 3dDespike only changed 1% of our voxels anyways, so it's not a huge deal to use cl=2.5. Obviously, if I use a higher c1 value, then more spikes will remain in the data, but this means that less data would be altered.

Thanks!