[Eeglablist] how to reject extreme values in continuous EEG data

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Wed Feb 11 18:29:40 PST 2015

Dear Nurit,

I hope you are talking about +/-150 microVolt (uV), not the millivolt.
You want to remove large amplitude artifact before ICA since ICA need to
pay very high cost to decompose it (my colleague said ICA can decompose
anything regardless of amplitude only when it is provided with infinite
length of data).

If you just want to cut them out by rejection, use trimOutlier. You can
install it from EEGLAB plugin manager ('File' -> ...) If you are using old
version of it, download it from here.

For a fancier solution, use clean_rawdata(). It has a sophisticated
cleaning method called Artifact Subspace Reconstruction (ASR).

> Why is that and how can I nevertheless reject extreme values such as
+/-150mV, in my case?

In many cases, because of historical reasons, 'data cleaning' tend to mean
epoch (==trial-based) rejection. In default EEGLAB, you can only perform
visual manual rejection for continuous data.

By the way +/-150 microvolt is not necessarily large amp. Eye blinks can
easily go beyond it.


On Mon, Feb 9, 2015 at 4:28 AM, Nurit Goldshuv-Ezra <nuritezra at hotmail.com>

> Hi there,
> I’ve been preprocessing continuous, unsegmented EEG data (4min length
> each) using EEGLAB and was wondering how I may reject extreme values
> (+/-150mv) after filtering, manual artefact removal and after the data got
> cleaned from eye artefacts using ICA.
> VALUES, I see that all options except for “reject components by map” are
> grey and hence not functioning. Why is that and how can I nevertheless
> reject extreme values such as +/-150mV, in my case?
> Many thanks for your support and help.
> Best,
> Nurit
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Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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