Hi Colm,

If your subjects are not adults, they may be more prone to
motion, making 0.2 perhaps too strict.

Bandpassing uses basically the fraction of frequencies up
to Nyquist as the fraction of DOF that are lost from the
operation (starting with the number of TRs).

For example, assume everything over 0.1 hz is removed in
the BP operation. Then if the TR is 2s (so Nyquist is 1/4 =
0.25), 60% of the DOF are lost to bandpass regressors,
with 40% remaining (0.1/0.25 = 0.4 remains, since bands
below 0.1 out of everything up to 0.25 are kept).

If there are 200 TRs, then 120 DOF are given up, with only
80 remaining. If the TR=5s (or more), then the Nyquist
frequency is 0.1 (or less), so there are no bands to remove.

Does that clarify it at all?

- rick