[Eeglablist] Filter distortion around boundary events

[Makoto Miyakoshi]

Dear Erickson

Is this really a distortion introduced by the filter? Rather, isn't it the
case that that portion of the data was poorly filtered i.e., your original
data, before filtering, had that noise constantly? Could you please check
your original data by eyeballing the raw time series and by checking power
spectral density?

Makoto

On Thu, Jul 12, 2018 at 10:33 AM Erickson <ericksonb.eng at gmail.com> wrote:

> Hello EEGLAB list,
>
> We are experiencing a strange artifact on only some of our EEG data. For
> some subjects, when we cut out portions of data (creating boundary events)
> and then filter (from 1 to 40 or 50hz) we observe a distortion around the
> boundary.
>
> Specifically, we see a rising or falling wave on either side of the
> boundary, with a fast oscillation riding on top of it. See here:
> https://drive.google.com/open?id=1yt6h_WLgI6jWAApVd52nwVLuiduYgXIH
>
> Although this data is from concurrent TMS-EEG recording, the distortion
> has nothing to do with the TMS pulse itself - we get the same
> boundary-related distortion when we filter after cutting out a random
> section of continuous data (a section with no TMS in it).
>
> I am at a loss - we've tried a few different filters and nothing seems to
> solve this issue. Meanwhile, on some subjects there is no boundary-related
> filter distortion at all! There is a lot of noise in the room but I'm not
> sure how that could create this specific issue.
>
> Any perspectives on this issue are appreciated! Thank you,
>
> Brian
>
> *Brian Erickson**, Ph.D.*
> *Postdoctoral Researcher, CogNeW Lab*
>
> *Drexel University*
> 3141 Chestnut Street
> Stratton Hall Room 320
> Philadelphia, PA 19104
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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