Dear Stefan,
> if I have a time series of activation (A) and rest (R) ARARAR with a period
> of 80 sec and I want to filter with low pass filter the high frequences
> of CSF pusations and breathing and I apply Gaussian low pass filtering,
> what FWHM for Gaussian filtering should I choose?
It depends on your sampling rate (TR) whether pulsations and breathing induced
changes are correctly sampled (TR<500ms) or aliased as low frequency
fluctuations (TR>500ms). I assume the latter case. You should then choose a
high-pass filter of 160s. The low-pass filter will not affect breathing and
pulsations because they do not appear as high-frequencies in the spectrum
(because they are aliased). However, the low-pass filter is helpful for (i)
supressing high-frequency noise and (ii) to "swamp" the original (unknown)
auto-correlation of the time-series with a known (determined by the filter)
autocorrelation.
-Christian
--
Dr. Christian Buechel
Neurologische Universitaetsklinik, Haus B
Universitaets-Krankenhaus Eppendorf
Martinistr. 52
D-20246 Hamburg
Germany
Tel.: +49-40-42803-4726
Fax.: +49-40-42803-5086
email:[log in to unmask]
www.uke.uni-hamburg.de/kliniken/neurologie/
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