Hi
The high-pass filter acts on a voxel-by voxel basis - no global mean
time course is being remove. And yes, there are some people who know
details - you might want to check the FEAT1 (pre-processing) talk
available on the FSL course website.
hth
Christian
On 30 Apr 2009, at 23:56, Enzo Tagliazucchi wrote:
> Hi all,
>
> I'm studying negative correlations between spontaneous BOLD signal in
> different voxels. It is known that substracting a global signal from
> all
> voxel might induce spurious negative correlations in the data. Thus
> I would
> like to know wheter or not the highpass filter in FEAT preprocessing
> acs
> locally (by filtering the BOLD signal in each separately) or
> globally (by
> computing some mean and substracting it from all the voxels). I
> suspect that
> in order to correct the scanner drift FEAT might substract a global
> signal
> from all the voxels.
>
> Does anybody know to some detail the algorithm FEAT uses to do
> highpass
> filtering and wheter or not it is purely local or global?
>
> thanks all!
>
> Enzo.
_______________________________________________
Christian F. Beckmann, DPhil
Senior Lecturer, Clinical Neuroscience Department
Division of Neuroscience and Mental Health
Imperial College London, Hammersmith Campus
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University of Oxford
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