Dear SPM experts:
This problem has haunted on me for quite a while. In the design matrix
generation procedures, I was asked whether to or not to specify a High-pass
filter. I was told before that the High-pass filter here actually is to
remove any low frequency components in my raw signal.So I applied this
filter, but after that, when I reviewed my design, I found out that my
design matrix has been smoothed by a kernel(although I do not know exactly
what it is), and I can tell that by naked eyes.
Here comes my question: Originally,I wanted to detrend(or filter) my
raw BOLD signal so that the linear drift or low frequency components would
not be any problem in further data analysis. But after applying this
High-pass filter, It only add some other frequency components to my design
matrix. It seems that my original goal has not been realized at all.
I've tried both ways(applying the High-pass filter and not applying it)
the final results are quite different to each other. Which one should I
trust?
Hope you guys have a better idea of what is going on about this filter.
Regards,
Jian
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