Hi all great and wise SPMers,
I am fairly new to SPM and had two, possibly naive, questions about
analysing a block design using SPM.
1) Is it ok to compare two conditions with different durations, i.e. make
a contrast "Block1-Block2" when the duration of Block1 = 36 seconds and
the duration of Block2 = 48 seconds? Does SPM average the activation
during the length of the duration or does it take the total activation for
the length of the duration?
2) Is it necessary to filter the signal when using a block design?
Because of the way we design/set-up the experiment, using the default
cutoff at 128 seconds would filter out a considerable amount of data. If
we increase the cutoff, we are afraid that signal to noise ratio would
decrease too much. Since it is impossible to differentiate between signal
and noise, it is hard to determine what's an appropriate cutoff and if we
need one at all.
Thanks,
Stanford
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