[FieldTrip] correction for movement tool

[Stolk, A.]

Hi Inna, You're welcome. The offline compensation method suggested (ft_regressconfound) is based on general linear modeling, and not on the  signal space separation method (Taulu et al., 2005, MaxFilter, Neuromag - not implemented in FieldTrip) you are referring to. Head movements blur the topography of the neuronal sources of the MEG signal, increase localization errors, and reduce statistical sensitivity. This GLM-based method is geared to improve statistical sensitivity rather than t opographical blurring and localization bias.  More specifically, it does not interpolate/extrapolate the magnetic field distribution measured by the sensor array to a magnetic field distribution that would have been measured had the sensors been at a desired location. Instead, it removes head movement related trial-by-trial variance from the data, by incorporating head position time-series into a general linear model.   A recently performed study (*) showed that this method improves statictical sensitivity without changing the pattern of activity. This is useful when you're testing an hypothesis, derived from a cognitive research question, because it reduces the risk of false negatives. With respect to your question; in case you are particularly interested in reducing  localization bias, I could recommend you to have a look at Uutela et al., NeuroImage, 2001. The forward calculation correction method suggested there incorporates head position information into the source reconstruction procedure. This method is implemented as ft_headmovement in FieldTrip. I cannot give you any numbers except from the ones reported there, but for all offline methods it holds that you need to be able to  measure the magnetic field distribution in order to know (and interpolate)   it. Hope this answered your question a bit. Feel free to ask more details. Yours, arjen (*) Stolk, Todorovic, Schoffelen & Oostenveld. Online and offline tools for head movement compensation in MEG. NeuroImage, accepted pending revisions. ----- Oorspronkelijk bericht -----
> Van: "Inna McGowin" <mcgoiv0 at wfu.edu>
> Aan: "FieldTrip discussion list" <fieldtrip at science.ru.nl>
> Verzonden: Woensdag 14 november 2012 14:31:15
> Onderwerp: Re: [FieldTrip] correction for movement tool
> Hello Arjen,
> Thanks for the links on the head motion correction.
> Could you please point a source or a reference on which the FieldTrip
> head motion correction method is based? Is it expansion of magnetic
> scalar potential in spherical harmonics or some other method? How
> accurate is the correction and what are the limitations for its
> application; in other words does it correct for motion up to 3 cm or
> beyond?
> What is the minimum motion that does not need to be corrected, for
> example we allow 5 mm?
> Thanks,
> Inna
> On Wed, Nov 14, 2012 at 5:07 AM, Stolk, A. < a.stolk at fcdonders.ru.nl >
> wrote:
> > Hi Nenad,
> >  
> > There are a few (online and offline) tools implemented in FieldTrip
> > to
> > deal with head movements in MEG.
> >  
> > For instance, have a look here:
> > http://fieldtrip.fcdonders.nl/example/how_to_incorporate_head_movements_in_meg_analysis
> >  
> > ft_regressconfound is particularly useful for removing
> > trial-by-trial
> > variance from the data that can be explained by head movements. We
> > found it to have a significant impact on statistical sensitivity.
> >  
> > At our institute, we use a real-time head localizer to reposition
> > the
> > subject between and within sessions (prevent/minimalize different
> > head
> > positions).
> >  
> > http://fieldtrip.fcdonders.nl/faq/how_can_i_monitor_a_subject_s_head_position_during_a_meg_session
> > Currently, it is implemented only for CTF systems (with the
> > continous
> > head localization upgrade) but we are working on extending
> > its implementation to other systems.  
> >  
> > Yours,
> > Arjen
> > > Van: "Nenad Polomac" < polomacnenad at gmail.com >
> > > Aan: fieldtrip at science.ru.nl
> > > Verzonden: Woensdag 14 november 2012 10:35:10
> > > Onderwerp: [FieldTrip] correction for movement tool
> > > Dear all,
> > > Do you have some tool which can correct data for the movements
> > > during
> > > MEG measurement? Our data were obtained on the CTF MEG 275 system.
> > > All the best!
> > > Nenad
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> --
> Inna McGowin
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