Hi Robin,

This has been unresolved within our group since the ACF method was introduced. The reasons for afni_proc.py using -detrend are that with the old FWHM method, it seemed to produce slightly more robust and expected results (at least in my testing), and because it should not have been detrimental. So there is a question about whether that translates to ACF. We have been thinking of taking that out as a default for a while now, but it clearly has not happened.

In any case, it seems reasonable to go either direction at this point, and lean towards not doing it, since we will probably shift that way as a default.

To turn it off in afni_proc.py (as of 6 days ago), add '-regress_est_blur_detrend no'.

Thanks,

- rick