[Eeglablist] How should I interpret this strange component?

[Yuan-fang Chou]

Dear Makoto,

I checked my raw data and found that there is significant large power in
about 0.5 Hz,just as shown in the link below.
https://www.dropbox.com/s/24fhfxcnqyvqyuc/raw_rythm.jpg
then I high-pass filtered at 1 Hz,the resulted power-spectra plot showed
that although frequency below 1 Hz was well attenuated, the power remained
significant in 1~1.5 Hz,which became the largest power in the spectra after
filter done.,just as shown in the link below.
https://www.dropbox.com/s/u66n4qu43ww4mfo/1Hzfiltered.jpg
So I think such a filter-left 1 Hz activity is the cause of  the 1 Hz
component in my ICA decomposition.And such a 1 Hz component seems to do
harm to my other components,just as shown in the links below:This is a
comparatively "good" component,but as you can see from the picture,the
baseline before 0 time point shows a slight 1 Hz activity,which makes the
baseline looks uneven.
https://www.dropbox.com/s/woaacj0426jjqel/good_component.jpg
So,I have 2 questions about it:
1. The slow rhythms,such as 1 Hz,seems to do harm to ICA decomposition.If
so,what's the reason behind this?Is it  because slow rhythms
 increase non-stationarity?
2.What can I do to resolve such a problem I met?

Thank you very much!

2012/5/23 Makoto Miyakoshi <mmiyakoshi at ucsd.edu>

> Dear Yuan-Fang,
>
> It's not the 1Hz high-pass filter introduced it additively, but the
> filter left the 1Hz activity as a result (I mean that's the only
> possibility I can think of). Imagine you have a data with a lot of
> sub- and near-1Hz activity as a broad spectrum (and this wave does not
> beat at 1Hz). What happens when you filter out sub-1Hz activity? 1Hz
> activity appears as a result, which beats at 1Hz.
>
> I'm still wondering what the artifact is. Please tell us what you find.
>
> Makoto
>
> 2012/5/22 Yuan-fang Chou <distancejay at gmail.com>:
> > Dear Makoto,
> >
> > Thanks for your comment.I will check my original dataset  soon.But could
> you
> > please explain to me how 1 Hz high pass filter could make such a strange
> > component? I'm really naive on this.
> >
> > 2012/5/23 Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> >>
> >> Dear Yuan-Fang,
> >>
> >> That is probably because you used a 1Hz high-pass filter. Probably
> >> your original dataset has a very strong sub-1Hz activity. Please check
> >> that possibility.
> >>
> >> Makoto
> >>
> >> 2012/5/22 Yuan-fang Chou <distancejay at gmail.com>:
> >> > Dear list,
> >> > I filtered my 64 channels data at 1~30Hz,and epoched it before running
> >> > ICA.Then I got  one of  the last a few components in the link below.It
> >> > appears that this component oscillates steadily at about 1 Hz
> >> > rhythm,which
> >> > looks rather strange. Could anyone tell me how to explain this
> >> > component's
> >> > activity?
> >> >
> >> > https://www.dropbox.com/s/mgadt1q7scn9vsf/component.PNG
> >> >
> >> > --
> >> > Yuan-Fang Chao
> >> > School of Psychology
> >> > SouthWest University
> >> > Beibei,Chongqing,China
> >> >
> >> >
> >> >
> >> >
> >> > _______________________________________________
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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
> >
> >
> >
> >
> > --
> > Yuan-Fang Chao
> > School of Psychology
> > SouthWest University
> > Beibei,Chongqing,China
> >
> >
> >
>
>
>
> --
> Makoto Miyakoshi
> JSPS Postdoctral Fellow for Research Abroad
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>



-- 
Yuan-Fang Chao
School of Psychology
SouthWest University
Beibei,Chongqing,China
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