[Eeglablist] Re-referencing drastically changes my power spectrum

[Ulrich Pomper]

Dear EEGlablist,

Dear Andreas, Gideon and Rozita,

Many thanks for your kind and helpful replies!

Inspired by your comments I went through my code again and found a bug 
that caused the weird looking spectrum (I unintentionally only filtered 
a subset of channels before the re-referencing).

Now the spectral results look almost identical between the two different 
orders of preprocessing steps.

My sincere apologies for not spotting that error before posting on the 
list (but your comments did still help me a lot!)!

Thanks again and have a great week 😊 !

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!Ff81b-i_PSdnm7hDAV_kqzG-eQDmmxqMOPlx_B62qviB-xiHdPN4WbKE_MawtY5KZe91Lg60WkjKDZ-P7mr_nbnUT6mNSBRpVw$  [3]
ulrich.pomper at univie.ac.at
+43-1-4277-47149 [4]

Am 22.08.2024 10:30, schrieb Andreas Widmann:

> Hi Ulrich,
> 
> Would you mind sharing an affected sample file and your code used for 
> analysis?
> 
> Best,
> Andreas
> 
>> Am 16.08.2024 um 17:09 schrieb Ulrich Pomper via eeglablist 
>> <eeglablist at sccn.ucsd.edu>:
>> 
>> 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 [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 [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
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Links:
------
[1] 
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[2] 
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[3] https://urldefense.com/v3/__http://www.rhythmsincognition.org__;!!Mih3wA!Ff81b-i_PSdnm7hDAV_kqzG-eQDmmxqMOPlx_B62qviB-xiHdPN4WbKE_MawtY5KZe91Lg60WkjKDZ-P7mr_nbnUT6mNSBRpVw$ 
[4] tel:+431-4277-47149