[Eeglablist] Filter distortion around boundary events

[Erickson]

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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