[Eeglablist] Filter distortion around boundary events

[Andreas Widmann]

Hi Brian,

please send a more detailed description of the filters (type, order, cutoff etc.) you used and how you marked the boundaries. Please include minimal code and provide a very small sample file somewhere (Dropbox) to reproduce the problem.

At first glance this looks like a typical notch filter artifact. However, this does not fit to your description. Thus, I would like to have a closer look into this.

Best,
Andreas

> Am 09.07.2018 um 23:05 schrieb Erickson <ericksonb.eng at gmail.com>:
> 
> 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
> 
> _______________________________________________
> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
> To unsubscribe, send an empty email to eeglablist-unsubscribe at sccn.ucsd.edu
> For digest mode, send an email with the subject "set digest mime" to eeglablist-request at sccn.ucsd.edu