[FieldTrip] Antw: Re: Source mapping for ITC / PLV

[Gregor Volberg]

Hi Nathan,

thanks a lot again. I will try this procedure.
Cheers,
Gregor


-- 
Dr. rer. nat. Gregor Volberg <gregor.volberg at psychologie.uni-regensburg.de> ( mailto:gregor.volberg at psychologie.uni-regensburg.de )
University of Regensburg
Institute for Experimental Psychology
93040 Regensburg, Germany
Tel: +49 941 943 3862 
Fax: +49 941 943 3233
http://www.psychologie.uni-regensburg.de/Greenlee/team/volberg/volberg.html

>>> Nathan Weisz  15.03.11 23.07 Uhr >>>
hi gregor,

it should basically work.

you may want to look at this paper:
http://www.ncbi.nlm.nih.gov/pubmed/18511307

just a Bardouille & Ross I would beam the complex FFT-coefficients using your spatial filter. that should be faster.
we recently did something very similar to localize the auditory steady state and it works nicely.

steps:
- calculate single trial FFT coefficients for the time / frequency period in which you see nice sensor level ITC
- calculate spatial filter (perhaps using a fixed orientation)
- multiply the coefficients with your filter
- convert to angles
- calculate ITC
- generate something that looks like sourceanalysis structure

good luck,
n

On 15.03.2011, at 20:15, Gregor Volberg wrote:

> Dear fieldtrippers,
> 
> I have a question on source reconstructions related to inter-trial coherence (or "phase-locking factor" the extent to which the phase of oscillations are locked to the onset of the evoking stimulus across multiple trials). For an ITC effect that I found on the sensor level, I did a source reconstruction for which I (1) computed an LCMV beamformer, (2) multiplied my sensor single trials with the beamformer filter to get the source single trials, and then (3) computed ITC for each single source position, over the source single trials. I hoped to see that the ITC is stronger at some source location than at others. But instead, the ITC was identical at every source position.
> 
> After unsuccessfully searching for an error in my code, I now wonder whether my strategy is valid at all, or whether my results (constant ITCs) are somewhat a consequence of how the beamformer filters the sensor data. If yes, is there a better strategy to do source reconstructions on indices that rely on phase consistency, like ITC or PLV? By saying "source" reconstruction of phase-locking indices, I do not mean to find a source of phase resetting or so, just phase-locking on the source signal level.
> 
> Any comments are welcome, thanks a lot in advance,
> Gregor
> 
> 
> 
> 
> 
> -- 
> Dr. rer. nat. Gregor Volberg  ( mailto:gregor.volberg at psychologie.uni-regensburg.de )
> University of Regensburg
> Institute for Experimental Psychology
> 93040 Regensburg, Germany
> Tel: +49 941 943 3862 
> Fax: +49 941 943 3233
> http://www.psychologie.uni-regensburg.de/Greenlee/team/volberg/volberg.html
> 
> 
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