Source coherence

Matsuhashi, Masao (NIH/NINDS) matsuham at NINDS.NIH.GOV
Thu May 19 20:14:35 CEST 2005


Hi Robert,

I am posting this message to the mailing list, with the original message
added to the bottom.

Thank you for your response.

1. Actually, the two frequencies are very close to each other. One is 5 Hz
and the other is 4.6 (60/13) Hz. Sampling is 600/sec. I used 6000 trial
length so the frequency resolution should be 0.1 Hz, but I am not sure
because MTM decreases the frequency resolution in terms of W.
The two reference signals are not independent, as they share the common
carrier frequency of 60Hz, but when we calculated the coherence sensor-wise,
they were separated relatively nicely.

2. I pushed the data to your ftp site. I hope it's working ok.
The filename is DICS_Matsuhashi_20050519.zip, containing 4 files.
Freq_01_050 and Source_01_050 are from condition 1, foi=5.0 Hz. Freq_01_046
and Source_01_046 are from condition 2, foi=4.6 Hz.

Regards,
Masao

------------------------------------------------
Masao Matsuhashi, MD, PhD
NINDS, NIH
Tel: 1-301-594-9139
E-mail: MatsuhaM at ninds.nih.gov
------------------------------------------------
> -----Original Message-----
> From: Robert Oostenveld [mailto:r.oostenveld at fcdonders.ru.nl]
> Sent: Thursday, May 19, 2005 7:08 AM
> To: Matsuhashi, Masao (NIH/NINDS)
> Subject: Re: [FIELDTRIP] sourcestatistics
>
> Hi Masao
>
> > signal. There are two reference signals simultaneously throughout the
> > recording, say, REF1 and REF2, with slightly different center
> > frequency, f1
> > and f2. I want to compare the coherence of cortical activity to
> > reference
>
> Just a question of general relevance. How well are the two frequencies
> separated, i.e. how far are they apart and what is your frequency
> resolution?
>
> > Is it quite common to see this kind of discrepancy in the result of
> > sensor
> > level coherence and source level coherence?
>
> No, I would not expect a very large difference between them. If the
> frequencies are far apart, the csd matrix for either f1 or f2 might
> contain more noise, affecting the filter (and hence the localization)
> more in one frequency than the other. But as I read your mail, I see no
> reason to assume that that is the case.
>
> > If you want to see the data, I will send them to you (frequency data
> > were
> > about 75M each, source 9M each).
>
> That would be nice, so that I can see it with my own eyes. Could you
> send both to ftp://m50-336.azn.nl/pub/incoming (login as anonymous) and
> send me a mail when they are there? The "incoming" directory is a
> drop-box, you cannot see what is in there (so you cannot read, but you
> can write) which might be a little confusing.
>
> > PS. If you think it is more appropriate to discuss this in the Mailing
> > List,
> > I can post this message to the list myself. I didn't do it, because the
> > update for DICS may not be available for public access.
>
> I think that it is interesting to have this discussion on the mailing
> list. Then also Jan-Mathijs and Pascal can think along.
>
> Robert


 =======================================================================
> -----Original Message-----
> From: Matsuhashi, Masao (NIH/NINDS)
> Sent: Wednesday, May 18, 2005 3:59 PM
> To: 'Robert Oostenveld'
> Subject: RE: [FIELDTRIP] sourcestatistics
>
> Hello Robert,
>
> I am now using your new DICS code with FieldTrip 0.9.6, and found a
> strange phenomenon. I've not yet checked into detail, but would like to
> have your idea.
>
> As you know, I am trying to calculate source coherence to external
> reference signal. There are two reference signals simultaneously
> throughout the recording, say, REF1 and REF2, with slightly different
> center frequency, f1 and f2. I want to compare the coherence of cortical
> activity to reference signal REF1 at frequency f1 (condition 1) and the
> coherence of cortical activity to REF2 at f2 (condition 2).
> The result of freqanalysis showed that coherence at sensor level (such as
> MRT31 x REF1) was much larger in condition 1 (up to 0.3) than in condition
> 2 (up to 0.05). However, when I calculate the source coherence from the
> above result using sourceanalysis, contrary to the above result, condition
> 2 showed larger source coherence. Actually, the maximum coherence was
> almost the same in both condition (about 0.02), but their distribution
> were quite different. The median value of the coherence in condition1 was
> 0.001, while in condition 2 it was 0.003.
>
> Is it quite common to see this kind of discrepancy in the result of sensor
> level coherence and source level coherence?
>
> If you want to see the data, I will send them to you (frequency data were
> about 75M each, source 9M each).
>
> Thanks,
> Masao
>
>
> PS. If you think it is more appropriate to discuss this in the Mailing
> List, I can post this message to the list myself. I didn't do it, because
> the update for DICS may not be available for public access.
>



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