[Eeglablist] phase shift and ICA

[Baris Demiral]

Actually the question can be asked in another way:

What happens to phase information when the ICA based artifact rejection 
is used, such that artifactual ICs are taken out, and the data is 
reconstructed back again with the rest of the ICs? Why would I prefer 
ICA correction rather than regression based correction?

Best,
Baris

On 04/04/2013 11:08 AM, Makoto Miyakoshi wrote:
> Dear Karlo,
>
> ICA is to generate spatial filter (EEG.icaweight*EEG.icasphere) and IC 
> activities. Scalp channel EEG remains unaffected.
>
> >Indeed, i like to know: how ICA may affect the  coherency between channel_1 
> (alpha-band) and channel_2 (beta-band)?
>
> ICA does not change anything, it just generates parallel data.
>
> Makoto
>
> 2013/4/3 karlo gonzales <thats_karlo at yahoo.com 
> <mailto:thats_karlo at yahoo.com>>
>
>     Thanks for your prompt reply. and my apology, if my question was
>     not clear enough.
>      My concern is not about phases between channels and ICs. Indeed,
>     i like to know: how ICA may affect the  coherency between
>     channel_1 (alpha-band) and channel_2 (beta-band)? does ICa will
>     shift phase of alpha or beta?
>
>     Thanks again,
>     Karlo
>
>
>
>     ------------------------------------------------------------------------
>     *From:* Makoto Miyakoshi <mmiyakoshi at ucsd.edu
>     <mailto:mmiyakoshi at ucsd.edu>>
>     *To:* karlo gonzales <thats_karlo at yahoo.com
>     <mailto:thats_karlo at yahoo.com>>
>     *Cc:* EEGLAB List <eeglablist at sccn.ucsd.edu
>     <mailto:eeglablist at sccn.ucsd.edu>>
>     *Sent:* Wednesday, April 3, 2013 9:36:51 PM
>     *Subject:* Re: phase shift and ICA
>
>     Dear Dr. Gonzales,
>
>     I suppose you mean you compare phases between channels and ICs.
>     It's not shift that makes difference between scalp channel ICs and
>     EEGs. Let me explain what it is. Let's say we have only 2 channels
>     and 2 ICs. The relation of scalp channel EEG and ICs are like this:
>
>     Channel 1 = 0.3 X IC1 + 0.7 X IC2
>     Channel 2 = 0.7 x  IC1 + 0.3 x IC2
>
>     Here I determined 0.3 and 0.7 arbitrarily but actually these are
>     determined by ICA. Anyway, when you compare Channel 1 with IC1 in
>     the above example, they are dissimilar to each other NOT because
>     of phase shift (unless IC1 and IC2 are similar, which is hard to
>     imagine since they are supposed to be temporally independent).
>
>     If the decomposition is like
>
>     Channel 1 = 0.99999 X IC1 + 0.00001 X IC2
>     Channel 2 = 0.00001 x  IC1 + 0.99999 x IC2
>
>     Then your Channel 1 and IC1 should be very similar.
>
>     Makoto
>
>
>
>     2013/4/3 karlo gonzales <thats_karlo at yahoo.com
>     <mailto:thats_karlo at yahoo.com>>
>
>         Dear Dr./Miyakoshi,/
>         /
>         /
>         /I am using  EEGLAB and ICA tools to clean EEG data. i
>         am recording EEG from a 64 channel cap (NEUROSCAN), with  a
>         fixed reference electrode, which is  located between CZ and CPZ. /
>         /i do not re-reference my data for further analysis.// So, i
>         just wonder, if applying ICA, would shift the phase of signals
>         (specially low frequency)? is there anyway to check it? /
>         /
>         /
>         /many many thanks for all your help and support,/
>         /Karlo/
>         /
>         /
>
>
>
>
>
>
>
>
>     -- 
>     Makoto Miyakoshi
>     Swartz Center for Computational Neuroscience
>     Institute for Neural Computation, University of California San Diego
>
>
>
>
>
> -- 
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
>
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