[Eeglablist] Low Pass Filtering and ERSP

[Marius Klug]

Dear Gözde,

I can also recommend the paper "Digital filter design for
electrophysiological data – a practical approach" by Widmann, Schröger, and
Maess on the topic. Although it is more focused on effects of filters on
ERP analysis, it is a fine overview on the actually quite complex topic of
digital filters!

All the best,
Marius

2016-12-15 11:05 GMT+01:00 Ahmad, Jumana <jumana.ahmad at kcl.ac.uk>:

> Dear Gozde,
> It is difficult to completely remove frequencies above your cutoff- you
> will likely reduce their amplitude, but most filters have a roll off. I
> think that due to attenuation, and the fact you will have modulated these
> frequencies that it is not safe to analyse them. Power (and phase) will be
> distorted in some frequencies more than others.
> Best wishes,
> Jumana
>
> -----Original Message-----
> From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces@
> sccn.ucsd.edu] On Behalf Of Gozde BAYER
> Sent: 14 December 2016 07:22
> To: eeglablist at sccn.ucsd.edu
> Subject: [Eeglablist] Low Pass Filtering and ERSP
>
>
> Dear EEGLAB List,
>
> During my raw EEG data recording from different subjects, I observed
> (online from the FFT plot of related software) some kind of 'noise'
> standing still at around 20-25 Hz and I could not get rid of that for some
> reason. So I decided to let EEG stream under this condition. Therefore I
> applied low pass filtering to the raw data at 20 Hz, and analyzed offline
> the remaining frequencies with EEGLAB. I created STUDY design for the
> purpose of the experiment. But when I plot ERSP of a specific channel, I
> could still distinguish frequencies surviving above 25 Hz. I checked from
> the workspace of Matlab as well.
> What could be the reason of that? Since I am sometimes getting this 20 Hz
> peak during raw EEG data recoding (by the way, I am trying to find out why
> this is the case), it is important for me to really understand the
> phenomenon behind that..Indeed, those frequencies just above 20 Hz are also
> of great importance for my future analysis..If they are able to survive
> -somehow- then would it be reliable to analyze beta frequency band under
> this condition?
>
> I appreciate any help,
> Best wishes.
>
> Gözde BAYER
>
>
>
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