# [Eeglablist] Question about the use of ICA and GC

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Mon Jul 28 15:29:33 PDT 2014

```Dear Salim,

> 1- Are the predicted S1(60) and S2(60) independent as the actual ones
which obtained using ICA.

If the S1(60) and S2(60) are the predictions made by i.e. AR model from
S1(1-59) and S2(1-59) respectively, then they are most likely independent.

> 2- The past values that it used to predict S1(60) and S2(60) are
independent. Does this independence affect the predict variables?

Yes, why not?

Makoto

On Sun, Jul 27, 2014 at 8:22 AM, Salim Al-wasity <salim_alwasity at yahoo.com>
wrote:

> Dear Mr. Miyakoshi
> Thanks for your reply. Let assumes that an ICA is applied to an observe
> matrix X (of 2 channels and 100 samples), therefore an S decomposed
> independent source signal is obtain.
> After that GC is used to find the connectivity between S1 and S2 (channel
> 1 and channel 2 of S), for instance to predict S1(60) and S2(60) based on
> the past values of S1 and S2 (for a predefined order), then:
> 1- Are the predicted S1(60) and S2(60) independent as the actual ones
> which obtained using ICA.
> 2- The past values that it used to predict S1(60) and S2(60) are
> independent. Does this independence affect the predict variables?
>
> Sincerely
> Salim
>
>
>   On Friday, 25 July 2014, 20:41, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
>
>
>  Dear Salim,
>
> ICA assures *instantaneous* independence, while GC calculates *temporal*
> causality. This means that ICA does not know what happens in the next
> moment, but GC does.
>
> By the way if you have more than 3 ICs for GC don't use GC but use RPDC or
> normalized dDTF.
>
> Makoto
>
>
> On Fri, Jul 25, 2014 at 4:41 AM, Salim Al-wasity <salim_alwasity at yahoo.com
> > wrote:
>
> Dears
> Have a nice day. Kindly I have a question regarding ICA:
> I have EEG data of (44 channels X 294000 samples)
>
> 1- I applied the ICA to separate the noise and find the ICs which are
> belong to brain activities.
> 2- I used the Granger Causality (GC) in SIFT to find the connectivity
> between these ICs and discover which component influence which. However I
> am not sure about the results that I have got.
>
> My question is that If I used ICA to decompose the EEG signal into their
> sources (hint: the decomposed ICs is much less than the actual brain
> sources), theoretically these ICs would be independent, and the use of GC
> would be useless since the latter algorithm search for the dependence
> across ICs?
> Or the ICA will minimize the mutual information, and the separated
> components will not be ~100% independent, therefore each component has more
> that one source, and GC  can find some influence across these components
> for the remaining not separated sources.
>
> Your cooperation is highly appreciated
>
> Yours
> Salim Al-Wasity
> PhD student
> Rehabilitation Centre
> Biomedical Engineering Department-School of Engineering
> University of Glasgow
> Glasgow-United Kingdom
> +44 742 371 4444
>
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>
>
> --
> 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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