Dear Muhammad,
How much you should add depends on how low your filter cutoff is, the
lower the more. I'd add at least twice the inverse of the cutoff to be
sure, e.g. 2 sec on each side for 1 Hz, 20 sec on each side for 0.1
Hz.
You can use spm_eeg_crop to remove the extra-padding.
Best,
Vladimir
On Tue, Mar 27, 2012 at 10:11 PM, Muhammad Adeel Parvaz
<[log in to unmask]> wrote:
> Dear Vladimir,
>
> In one of your slides from the SPM course, you mentioned
>
> "It’s better to filter before epoching unless only small part of the data is
> relevant. As an alternative one could pad the epochs of interest with extra
> data and discard it later."
>
> I am in a similar situation in which I am interested in analyzing a small
> part of a relatively large data set. Therefore, I would like to do high-pass
> filter after epoching. I am originally interested in the epoch from -200 to
> 1000ms and so I imagine that I should epoch -500 to 1300ms and then do
> high-pass filtering. Is that right? If I do it that way, how do I trim the
> epoch back to -200 to 1000ms?
>
> Thanks
> Muhammad
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