Significance of coherence

[jan-mathijs schoffelen]

Dear Vladimir,

I usually use a shift predictor to test for this (computing coherence
between signal A and a shuffled set of trials for signal B: provided
both signals are not phase-locked to trial onset).
However, this only works well when you are estimating for coherence
between non-volume conducted activities.
When coherence is estimated between two reconstructed dipoles, the
amount of volume conduction is generally too high for this method to
make sense.
In other words, you will always get "significant" coherence in this
case.
The other way would be to use the traditional thresholding which is
applied for example in Kilner et al 2001 J Neurosci. But this
obviously suffers from the same problems as the
shift predictor.
Jackknifing could also be used with a t-test against 0, but again
with the same problem.

Yours,

Jan-Mathijs


On Jul 16, 2008, at 12:38 PM, Vladimir Litvak wrote:

> Dear all,
>
> Could you point me to the present state of the art method to determine
> significance of coherence? I'm not talking about comparison between
> two conditions and not about activation to baseline comparison. Just
> you have some stationary signals, compute coherence and want to say
> whether it's real. I suspect there is no ideal solution, but what is
> the most accepted presently? Can jackknife implemented in
> freqdescriptives be used for that? Any other suggestions.
>
> Thanks,
>
> Vladimir
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users
> of the FieldTrip  toolbox, to share experiences and to discuss new
> ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/
> archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.