Hi Helmut,

Figure 4 in this paper might also be interesting:

The paper suggest that modeling polynomians is more accurate than high-pass
filtering. However, they are not explicit about the type of filter they use
and I don't see why there should be a huge difference between e.g. DCT
filtering vs. adding DCT regressors to the model (which used to be the
default in SPM).


2015-06-17 19:21 GMT+02:00 H. Nebl <[log in to unmask]>:

> Dear Torben,
> Yes, I've checked the implementation in AFNI (Legendre polynomials), the
> order is based on 1 + floor((duration of the session in s)/150 s), with the
> 150 s probably based on the same early event-related fMRI studies that
> resulted in the default 128 s in SPM. Thus in case of block designs with
> long intervals, long block lengths one would run into the same issues
> (adjust to HPF to keep slow frequency signal within the model, remove the
> noise but also remove possibly major parts of the signal) with polynomial
> regressors. I hadn't really thought about that, as the linked papers
> dealing with polynomials usually didn't go beyond 4th or 5th order.
> Best
> Helmut