[Eeglablist] phase shift and ICA

[Makoto Miyakoshi]

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>

> 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>
> *To:* karlo gonzales <thats_karlo at yahoo.com>
> *Cc:* EEGLAB List <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>
>
>  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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