[Eeglablist] EEGLAB: Epoching and ICA. In which order?

[Makoto Miyakoshi]

Dear Alice, Malte, and Xiaonan,

To reply to your question, I added description to my Wiki page. Please
follow the link below.
https://sccn.ucsd.edu/wiki/Makoto%27s_preprocessing_pipeline#What_is_assumption_of_stationarity_in_ICA.3F_.2809.2F11.2F2019_updated.29

> There is no definite solution for this question.
> It seems to me there's no absolute right or wrong protocol for this.

Qualitatively speaking, if you compare ICA results with and without
epoching, the difference may be small and even negligible. For example, in
the extreme case, if you are analyzing mismatch negativity where there is
basically zero between-trial interval, the results will be identical!
However, qualitatively speaking, there is benefit in epoching first (data
length being permitted). The difference would be maximum if your continuous
recording currently includes '5-min resting period' between blocks for 5
times... epoching data excludes these resting-period data, which certainly
increases data stationarity and makes it easier for ICA to focus on
event-related brain dynamics to decompose.

If you have questions or extra discussion, please let me know!

Makoto

On Wed, Sep 11, 2019 at 5:32 AM Alice Grazia <alicegrazia94 at gmail.com>
wrote:

> Thank you all for the useful answers!!
>
> Best Alice
>
> Il giorno mar 10 set 2019 alle ore 21:40 Xiaonan L. Liu <
> liuxiaonan87 at gmail.com> ha scritto:
>
> > Hi Alice,
> >
> > It seems to me there's no absolute right or wrong protocol for this . I
> > usually prefer doing epoch before ICA and the reason is by epoch, you can
> > get rid of noisy portions of your data (e.g. at the beginning, breaks and
> > the end etc). It seems to me what's really important is you need clean
> data
> > in order to get good ICA decomposition and epoch is somewhat a way to get
> > cleaner data.
> >
> > Best,
> > Xiaonan
> >
> > On Tue, Sep 10, 2019 at 9:53 AM Alice Grazia <alicegrazia94 at gmail.com>
> > wrote:
> >
> >> Hi all,
> >> I have this doubt that I could not solve by myself. Maybe it is more a
> >> theoretical question than a programming question, but I'm performing
> >> time-frequency analysis with EEGlab software for my master thesis and
> I'm
> >> not sure whether it is more correct to perform ICA and epoching in a
> >> precise order. I found some recommendations (EEGLAB tutorial 2004)
> saying
> >> that it is advisable to perform ICA on a greater amount of data as
> >> possible. However, if I run ICA on EEGLAB before epoching, I cannot
> have a
> >> good visualisation of the ICA components (only the maps and components
> >> scroll). Instead, I have seen in a tutorial by Mike Cohen, that he
> >> performs
> >> epoching before ICA, so there is the possiblity to look at each
> component
> >> latency and frequency before rejecting. Personally, I found myself
> better
> >> with the second method, but I am not sure wheather it is correct or not.
> >> I hope you can help me in this dilemma! Thank you!
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-- 
Makoto Miyakoshi
Assistant Project Scientist, Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego