[FieldTrip] simulating a dipole with a real headmodel and using DICS to locate it misplaces the source

[Thomas Hartmann]

thanks a lot, tzvetan! i seem to have misinterpreted the meaning of 
cfg.absnoise. i thought it had the same scale as the cfg.dip.amplitude.

thanks again and all the best,
thomas


Am 27.02.2017 um 14:23 schrieb Tzvetan Popov:
> Hi Thomas,
>
> you might have solved it. In case not, I changed :
> cfg.relnoise = 5;
>
> and the amplitude of the baseline signal to
>
> cfg.dip.amplitude = .1;
>
> and it worked. You simulate the location at 9 0 6 and it comes out 
> (NAI) at 90.5 -.5 59.5 (see attached).
>
> best
> tzvetan
>
>
>
>> hi,
>>
>> i wanted to see whether i can simulate a dipole with the data 
>> provided by the tutorial and use the DICS beamformer to see where the 
>> source gets projected.
>>
>> the code i used is in the attached file.
>>
>> it expects the data you can download from here: 
>> ftp://ftp.fieldtriptoolbox.org/pub/fieldtrip/tutorial/beamformer/
>>
>> in a folder called "beamformer".
>>
>> the puzzling thing is that i do not seem to manage to have it project 
>> the sources anywhere near to the original dipole in the simulation. 
>> the center of the head bias come out nicely if neither baseline 
>> correction or NAI calculation is used. i also checked whether the the 
>> coordinate system of the volume and the grid i generate match. i also 
>> checked whether the chosen dipole shows up at the correct location 
>> when i plot it on the head model.
>>
>> so, my question is: what do i not get here? maybe there is something 
>> wrong with my script? maybe ft_dipolesimulate is not supposed to be 
>> used that way?
>>
>> i would really appreciate any suggestions.
>>
>> best,
>> thomas
>>
>> ps: i also tried with eloreta and a simple dipole fit. the results 
>> look slightly different but not really any better...
>>
>> -- 
>> Dr. Thomas Hartmann
>>
>> Centre for Cognitive Neuroscience
>> FB Psychologie
>> Universität Salzburg
>> Hellbrunnerstraße 34/II
>> 5020 Salzburg
>>
>> Tel: +43 662 8044 5109
>> Email: thomas.hartmann at th-ht.de <mailto:thomas.hartmann at th-ht.de>
>>
>> "I am a brain, Watson. The rest of me is a mere appendix. " (Arthur 
>> Conan Doyle)
>>
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>
>
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-- 
Dr. Thomas Hartmann

Centre for Cognitive Neuroscience
FB Psychologie
Universität Salzburg
Hellbrunnerstraße 34/II
5020 Salzburg

Tel: +43 662 8044 5109
Email: thomas.hartmann at th-ht.de

"I am a brain, Watson. The rest of me is a mere appendix. " (Arthur Conan Doyle)

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