[Eeglablist] Re-referencing drastically changes my power spectrum

[Makoto Miyakoshi]

Hi Ulrich,

Your implicit assumption there is that the spatial power distribution
across [broadband], [2-12] Hz, and [13-30] Hz be all the same. But the data
seem to indicate that it is not the case.
I predict that the first two must be more or less similar because [2-12] Hz
captures a good portion of 1/f power distribution, while the first and the
third could be very different because EMG's spatial distribution is known
to be concentrated in peripheral electrodes.

I follow Andreas' request--I want to see the data too.

Makoto

On Sun, Aug 18, 2024 at 7:50 AM Ulrich Pomper via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Dear EEGlab list,
>
> I have a question regarding to order of two common preprocessing steps:
> filtering and re-referencing to common average.
>
> In my current EEG study, I initially filter the raw, continuous data
> into low (2-12 Hz) and high frequency components (13 - 80 Hz), and
> afterwards re-reference the data to common average. However, this
> re-referencing step really messes up the spectrum of the data in a way
> that makes me suspect an error (please see panels 7 and 8 in this figure
> [1]).
>
> When I re-reference first and filter second, on the other hand, the
> spectrum stays intact and the data seem OK (see panels 5 and 6).
>
> I was hoping that someone might be able to explain to me what is going
> on here, and potentially confirm that re-referencing first and filtering
> second is actually the correct way to go.
>
> I'd highly appreciate any input!
>
> Many thanks,
>
> Ulrich
>
> --
> Dr. Ulrich Pomper
>
> Senior Scientist
> Department of Cognition, Emotion, and Methods in Psychology
>   University of Vienna
>   Liebiggasse 5
>   1010 Vienna
>   Austria
>
>
> https://urldefense.com/v3/__http://www.rhythmsincognition.org__;!!Mih3wA!FGS_Heq7qxqfOnJQRY9iWkPCeyqHn2JXpN813UzKIfwO9NvF21ZtZ0Kice2TBxBkbfGiZ_gKEek0myyUErlLBlsFWQu_mv1bog$
> [2]
> ulrich.pomper at univie.ac.at
> +43-1-4277-47149 [3]
>
>
>
> Links:
> ------
> [1]
>
> https://urldefense.com/v3/__https://drive.google.com/file/d/1iBnYCQiLmWAEd1rLMLcHYqD3AHbD5dRP/view?usp=sharing__;!!Mih3wA!FGS_Heq7qxqfOnJQRY9iWkPCeyqHn2JXpN813UzKIfwO9NvF21ZtZ0Kice2TBxBkbfGiZ_gKEek0myyUErlLBlsFWQt8C5gzOA$
> [2]
> https://urldefense.com/v3/__http://www.rhythmsincognition.org__;!!Mih3wA!FGS_Heq7qxqfOnJQRY9iWkPCeyqHn2JXpN813UzKIfwO9NvF21ZtZ0Kice2TBxBkbfGiZ_gKEek0myyUErlLBlsFWQu_mv1bog$
> [3] tel:+431-4277-47149
> _______________________________________________
> 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
>