[FieldTrip] help with dipole position and orientation

[jan-mathijs schoffelen]

Hi Fred,

> In a paper by Osipova et al. (2008) I read that the position can
> be chosen based on the sensor array of a CTF system with respect
> to head coordinates.
> In this paper the dipole position was chose to be r = [-5 0 1] which
> should correspond to a dipole close to the hemispheric midline and
> in the occipital cortex.
> 
> Can anyone tell me based on which data / how these coordinates were
> chosen? I have been searching the grad structure of my data
> for comparable info, but did not find anything. Neither did I looking
> at cfg.layout.pos.

Why would you want to look into the grad structure, or in the layout.pos? I guess the most straightforward would be to ask one of the authors of said paper why they chose the parameters.
Very generally, I think that the coordinates were chosen based on knowledge with respect to the coordinate system. Indeed, the negative x-axis points to the back, and a y-coordinate of 0 represents the midline.

> My second question concerns the dipole moment.
> Am I right in assuming the following:
> 
> cfg.dip.mom = [1 0 0] % dipole points towards NAS
> cfg.dip.mpm = [-1 0 0] % dipole points away from NAS
> 
> cfg.dip.mom = [0 1 0] % dipole points towards LPA
> cfg.dip.mom = [0 -1 0]% dipole points towards RPA
> 
> cfg.dip.mom = [0 0 1]% dipole points towards vertex
> cfg.dip.mon = [0 0 -1]% dipole points away from vertex
> 

Yes, that's correct.

Best,

Jan-Mathijs


> Any help or suggestions would be highly appreciated.
> 
> Best,
> Fred
> 
> 
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

Jan-Mathijs Schoffelen, MD PhD 

Donders Institute for Brain, Cognition and Behaviour, 
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands

Max Planck Institute for Psycholinguistics,
Nijmegen, The Netherlands

J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20121020/b42107cf/attachment-0002.html>