Question

Asked 10 September 2019

German Center for Neurodegenerative Diseases

EEGLAB: Epoching and ICA. In which order?

Hi all,

I have this doubt that I could not solve by myself. 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 reccomendations in EEGLAB tutorial manual 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!

EEGLAB

ICA

Nik Murphy

Baylor College of Medicine

Marco Cursi

San Raffaele Scientific Institute

Dr. Indrajit Mandal

Rajiv Gandhi Institute of Technology, Bangalore

Rainer Duesing

Osnabrück University

Michael X Cohen

Radboud University

Patrick Friedrich

Forschungszentrum Jülich

Dear Alice,

Applying the ICA before epoching aims at correcting systematic/re-occuring artifacts (saccades, blink, heart rate artifacts). As these artifacts are best displayed in chunks of your data that may not even lie within your epoch of interest, I would suggest sticking to the EEGLAB recommendation.

To be honest, I have not yet seen a paper in which the authors applied ICA (with the aim of identifying artifacts) after segmentation/epoching. But maybe I just didn't screen enough papers for exactly that ^^"

Best regards,

Pat

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1 Recommendation

Elliott Jardin

Miami University

Hi Alice,

I have always run the ICA before Epoching. Similar to Patrick's answer, I agree that it's probably best to stick to EEG labs recommendation.

This is because random and systematic noise will occur throughout the entire recording. If the data are broken up just into Epochs, it will lose the systematic pattern of the noise and the ICA may not be able to identify the noise in the recording as well. To me this makes sense... hopefully this help you.

Best of luck,

-Elliott

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1 Recommendation

Caitriona L Douglas

Dalhousie University

Hello,

Steven Luck, who is pretty widely regarded as the god of ERP analysis methods recommends that people first visually inspect and reject highly abnormal data (like a period of extreme muscle noise), then perform ICA, then epoch.

Here is a post about it on his site with a full outline of his recommended data processing/analysis steps: (The clearest step by step outline is near the bottom of the article)

https://erpinfo.org/order-of-steps

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