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

[Malte Anders]

Hi Alice,

Let me put it this way: if ICA after epoching works best for you, go that
way. There is no definite solution for this question.

My personal experience (just my opinion, dont know if this is correct): if
you have few epochs (e.g. 10) from, lets say, -1 to 2 seconds that contain
your components of interest and your inter-episode interval is very long
(lets say, 60 seconds), your whole data is 10 minutes long but only
contains 30 seconds of data with components of interest. Thats only 5% of
your data containing episodes/components of interest, the rest is pretty
much nonsense. In that case I'd epoch before ICA.
If a higher percentage of your data contains components you're interested
in (even artifactual components if you use ICA for artifact rejection) I'd
also try doing ICA before epoching, with fluent borders (no "definitive"
percentage from which on going the other way round).

In my use cases (small epochs, lenghy data with 95% of EEG I am definitely
not interested in) I personally epoch before carrying out ICA.

But, as put in the first sentence: you already did your homework and tried
both, just do what gives you the best results.

Eeglab tutorial seems to be rocket science if you read it for the first
time, but after repeating everything over and over again I have a slight
feeling that users (me included) get more and more dogmatic...

Kind regards from Germany,
Malte

Alice Grazia <alicegrazia94 at gmail.com> schrieb am Di., 10. Sep. 2019, 18:53:

> 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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