[Eeglablist] sift and phase

[Iman M.Rezazadeh]

Hi EEGLABers,

I have been thinking about this issue. Basically, we transfer the data from
the sensor space to the source space to deal with the volume conductance
problem and also dealing with less signal sources to create MVAR model. If
we do MVAR model on electrode space then one might ask question about which
electrode(s) to select and how to deal with VC problem? Also doing
connectivity study on the sensor space might fraught with challenges in
interpretation and high false positive rates.  It has been shown that the
combination of MVAR+BSS works compared to either BSS-alone or doing granger
causality on the senor space.

 

In addition , I have come up with an idea about the relation of Causality in
the source space and sensor space:

 

X(t)=M.S(t); where X(t) is the time series of Sensor space data for all
electrodes and M is the Mixing matrix

S(t+1)=R S(t) +N(t) ; R is the Relationship Matrix btw Sources and N is the
Noise matrix

M-1X(t+1)= R.M-1.X(t)+M-1N(t);

X(t+1)=M.R.M-1.X(t)+N(t);

X(t+1)=R'.X(t)+N(t);

So, 

1-     the amount of the noise in the senor and source spaces does not
change . 

2-     On the other hand there is a relationship btw Relation matrices in
the sensor and source spaces which is M.R.M-1=R'. In general, R<> R' but one
can define M to have R=R'. 

3-     The point is in the source space you can great R with a few number of
dipoles however in the electrode space the relationship btw the electrodes
is not clear, but I it might be the case that the electrodes that have high
mixing values are more correlated to each other ( it needs some simulation
and test). 

4-     I think calculation coherence in the sensor space makes more sense
but if we want to do causality analysis and MVAR modeling source space is
more applicable. So, the 'elimination' of phase relationship in the sensor
space may cause alternation in coherence but it does not do anything with
the causal relationship btw  sources and in given condition electrodes.

 

These are my thought and would be happy to hear more comments !

Best,

Iman

 

 

 

From: eeglablist-bounces at sccn.ucsd.edu
[mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Adrian Willoughby
Sent: Monday, July 15, 2013 10:04 PM
To: mmiyakoshi at ucsd.edu
Cc: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] sift and phase

 

Hi all,

 

I've been thinking about this recently too and came across this - which may
be a reasonable place to start the discussion.

 

http://www.appliedneuroscience.com/COHERENCE-DevNeuropsy-WEB.pdf

 

I'd also be interested in hearing other's opinions.

 

Adrian

 

On Mon, Jul 15, 2013 at 7:32 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
wrote:

Dear Robert,

 

I've seen the same claim in this list, so you may want to find it in the
archive. I did not find any convincing argument in their claim. If you know
other papers I'd be interested in knowing.

 

Makoto

 

2013/7/15 robert coben <drcoben at gmail.com>

We have recently started using sift for multivariate and directional
coherence analyses with very interesting findings, at least initially. My
question is this. There are some critics of ICA that suggest it alters phase
relationships in the EEG rendering any coherence  or network analyses
invalid. I would love to hear the opinion of those in this group about this
notion.

Thanks,

Rob
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-- 

Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego


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