Dear Stefan,
>Dear SPMers,
>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?
>
The reason for the low pass filtering is to ensure the validity of the
analysis (by informing the design matrix of the "appropriate" degress of
freedom of the resulting time series whose autocorrelation should now be
dominated by the filter). I tend to use the default 4mm FWHM. This is
really independent of the period of your experimental condition.
Note also that unless you use a very short TR you will undersample
pulsations and breating causing them to be aliased all over the frequency
band, i.e. you will no longer see them as exclusively high frequency.
>Thank you, Stefan (Innsbruck, Austria)
Good luck Jesper
Jesper Andersson
Wellcome Dept. of Cognitive Neurology
12 Queen Square
London WC1N 3BG
phone: 44 171 833 7484
fax: 44 171 813 1420
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