[Eeglablist] Questions about ICA component rejection in EEGLAB

[Makoto Miyakoshi]

Dear Liu,

(1) I've never noticed them until I confirmed it now. You are right, they
are grayed out. They are not available from GUI at least, and I don't know
if there are off-GUI functions for them.

(2) Plot - Component ERPs runs pop_envtopo() where you can evaluate percent
variance accounted for (pvaf) and related measures that tell you each IC's
contribution to scalp ERPs. ICs with lower numbers have high variance since
they are sorted so after ICA. For example your IC90-IC100 would not have
even 1/10 of variance of IC1 (could be even 1/100 which is 40dB smaller in
FFT plot). This means that discarding 50 out of 100 ICs does not mean
discarding 50% of data (variance). If you want to measure how much 'data'
are rejected, you may check pvaf as one of measures.

Makoto

2013/2/25 Liu Pan <pliu261 at gmail.com>

> Dear eeglabbers,
>
> I have 2 questions about the ICA component rejection function of EEGLAB:
>
> (1). I read the paper "Automatic artifact rejection for EEG data using
> high-order statistics and independent component analysis" by Drs. Delorme,
> Makeig, and Sejnowski.
> http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&ved=0CEAQFjAB&url=http%3A%2F%2Finc.ucsd.edu%2Fica2001%2F117-delorme.pdf&ei=JakrUbjhCMe30gHevIGoCQ&usg=AFQjCNGwjRtjnTiRvUxguqJNAejvoD6a7g&sig2=9BQuz03YEzUOszEreafYgA
> In *section3.3 *the authors mentioned that in addition to manually and
> visually rejecting ICA components based on the component properties, there
> is a function in EEGLAB software by which one can set an adequate rejction
> threshold for three high-order statistical measures (the entropy of the
> activity of the component, the kurtosis of the activity, and the kurtosis
> of the components' spatial map), then one can automatically detect and
> reject components (insteady of mannually doing so). In search of this
> function in EEGLAB, I found that in the *Tools--Reject data using
> ICA--Reject components by map* function, there are 3 buttons at the
> bottom of the popped out window (*set threshods, see comp. st..., see
> projection)* which appear to be grey and inactive. I suppose these
> buttons, especially the on *set threshods, *are relevant to the automatic
> ICA component rejection function mentioned in that paper.  However, these
> buttons are not active and cannot be used. According to the *Help* file
> of this function, *"if the function POP_REJCOMP is ran prior to this
> function, some fields of the EEG datasets will be present and the current
> function will have some more button active to tune up the automatic
> rejection."*  I searched *POP_REJCOMP* function but failed to get a clue
> from the tutorial nor the previous discussion list. Could anyone give me
> any suggestion about this? Are these inactive buttons the ones for
> automatic ICA component rejection?  If yes, how can I get them to work?
>
> (2). While doing ICA component rejection, how many of the original
> components would you reject? I sometimes rejected almost half of them, is
> it too much or not?
>
> Thank you very much for any of your input in advance! Pan
>
> --
> Liu Pan, PhD. Candidate
> Neuropragmatics and Emotion Lab (Pell Lab)
> School of Communication Sciences and Disorders
> Faculty of Medicine, McGill University
> Montreal, Canada
>
>
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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