Hi Sam
bandpass and detrending can indeed by redundant - SPM doesn't do a high
pass filter as in filtering the frequencies out before analyses, instead
is used a set of sines in the design matrix to capture this (see
SPM.xX.K.X0) which (linearly) remove trends (which are not linear
--other approaches exist as well such as using high order polynomials in
your design matrix. Everything being in the same projection space is a
more elegant way to test for specific effects.
cyril
> Hi,
>
> I have seen that many software packages detrend the fmri timeseries in addition to applying bandpass filtering. But isn't detrending redundant if the data is already bandpass filtered? I thought detrending removes linear trends such as scanner drift, but these are also removed when applying a high-pass filter. Or does detrending capture other sources of noise?
>
> Thanks,
> Sam
--
Dr Cyril Pernet,
Senior Academic Fellow
Neuroimaging Sciences
Centre for Clinical Brain Sciences
Chancellor's Building, Room GU426D
The University of Edinburgh
49 Little France Crescent
Edinburgh BioQuarter EH16 4SB
[log in to unmask]
tel: +44 (0)131 465 9530
http://www.sbirc.ed.ac.uk/cyril
http://www.ed.ac.uk/edinburgh-imaging
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
|