[Eeglablist] high frequency oscillation- eeg advice

[Makoto Miyakoshi]

Dear Jumana,

It's a bad idea to perform ICA with 0.1Hz high-pass filtered data. The
cutoff frequency is too low. See this page and the referenced paper.

https://sccn.ucsd.edu/wiki/Makoto%27s_preprocessing_pipeline#High-pass_filter_the_data_at_1-Hz_.28for_ICA.2C_ASR.2C_and_CleanLine.29

> A 30Hz low pass does not help to get rid of the oscillation, which is
really significant in the data.

Check the channel frequency spectra and tell me if you see peaks in it. If
necessary, you can cut it off using a designed low-pass filter (not like
Butterworth...)

> I use a butterworth filter, which is good for ERP analysis with low phase
distortion.

Do not make qualitative judgement just because something is NOT a classic
Butterworth. Of course, if the attenuation is small, the phase 'distortion'
is small. But if such small attenuation is not useful, it does not help at
all! Also, be careful with the word 'phase'. Particularly people who do not
know basics of signal processing believe phase as some magical thing. If
you are not performing Granger Causality Analysis or something, you don't
need to be so worried about phase issue in practice.

> I also already run ICA, but in some datasets there is a very significant
high frequency oscillation.

Remember, to eliminate this is more important than being afraid of
qualitative phase issue.

> However, I can see the high frequency oscillations in my ERP, which is
not ideal and now I need to try and get rid of it further.

Can I filter again on top of the data which already has already undergone
ICA- I only use ICA to remove blinks?

You'd better to filter the data on continuous state. If you need to filter
the epoched data, the half of filter length from both ends becomes
unreliable.

> Should I do cleanline, although it would have to be after ICA now- I read
this is not advisable.

> Should I use a notch filter?

If you see > 20dB line noise, Cleanline may not help. In this case, I would
simply apply a designed low-pass filter, either Hamming (-50dB) or Blackman
(-70dB) using firfilt(). See 'Tools' -> 'Filter the data' -> 'Windowed sinc
FIR filter'.

There are different guys saying different things about data preprocessing.
It is confusing, I know! The only good solution for this is to become an
engineer yourself...

Makoto



On Tue, Jan 24, 2017 at 7:00 AM, Ahmad, Jumana <jumana.ahmad at kcl.ac.uk>
wrote:

> Hi  Everyone,
>
> I am running a large scale ERP analysis. I filtered 1-40Hz (ICA AMICA), or
> 0.1-40Hz for the ERP dataset. A 30Hz low pass does not help to get rid of
> the oscillation, which is really significant in the data. I use a
> butterworth filter, which is good for ERP analysis with low phase
> distortion.
>
> I also already run ICA, but in some datasets there is a very significant
> high frequency oscillation.
>
> I do not use cleanline, which is not typical in the literature I have been
> basing my pipeline on.
>
>
>
> However, I can see the high frequency oscillations in my ERP, which is not
> ideal and now I need to try and get rid of it further.
>
> Can I filter again on top of the data which already has already undergone
> ICA- I only use ICA to remove blinks?
>
> Should I do cleanline, although it would have to be after ICA now- I read
> this is not advisable.
>
> Should I use a notch filter?
>
>
>
> Any help would be appreciated.
>
> Best wishes,
>
> Jumana
>
>
>
> *------------------------------------------*
>
> *Jumana Ahmad*
>
> Post-Doctoral Research Worker in Cognitive Neuroscience
>
> *EU-AIMS Longitudinal European Autism Project (LEAP) & SynaG Study*
>
> Room M1.09. Department of Forensic and Neurodevelopmental Sciences (PO 23)
> | Institute of Psychiatry, Psychology & Neuroscience | King’s College
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>
>
>
> *Phone:* 0207848 0260| *Email:* jumana.ahmad at kcl.ac.uk
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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