[FieldTrip] Appending data from two sessions for ICA

[Jörn M. Horschig]

Hi Giorgio,

you could also try to use ft_megrealign, which projects the channels of your
data to source space and then projects the activity back to some predefined
set of sensors. I have never tested how well this function works, but it was
intended for such purposes back then ;)
http://fieldtrip.fcdonders.nl/reference/ft_megrealign
The documentation states that it's for timelocked data, but I am 100% sure
that the code will only work on  raw data. Maybe test both, simply copying
over the sensor description as Eleke (I like that typo!) suggested and
compare it with what ft_megrealign gives you and decide for yourself what
you prefer best/seems to give most reliable results.

Best,
Jörn



--

Jörn M. Horschig, Software Engineer
Artinis Medical Systems  |  +31 481 350 980 

> -----Original Message-----
> From: fieldtrip-bounces at science.ru.nl [mailto:fieldtrip-
> bounces at science.ru.nl] On Behalf Of Eelke Spaak
> Sent: Wednesday, February 11, 2015 12:17 PM
> To: FieldTrip discussion list
> Subject: Re: [FieldTrip] Appending data from two sessions for ICA
> 
> Dear Giorgio,
> 
> FieldTrip kind of 'protects' the users against themselves when appending
> different data sets, because if sensor positions are substantially
different
> then this could be a serious problem. However, if you are certain the
sensor
> positions are highly comparable (e.g. if you've used interactive
realignment
> during the recording session) you can simply take the .grad field (which
> contains the sensor positions) of one of the datasets (best to use the
first
> one, if that's the one you aligned to) and put it in the combined data
> structure.
> 
> Best,
> Eleke
> 
> On 11 February 2015 at 10:46, Giorgio Arcara <giorgio.arcara at gmail.com>
> wrote:
> > Dear Fieldtrip users,
> >
> > I recorded some MEG data in two separate recordings. The recordings
> > were one immediately after the other, with a short pause (of few
> > seconds) in the middle. In my recording I stored the head position
> > continuously (CTF-system).
> >
> > My aim is to combine the data from the two recordings to run a single
> > ICA, with the aim of identifying artifacts.
> >
> > After the preprocessing and after using ft_appenddata I receive I
> > warning because there is an inconsistency in sensor positions stored
> > in the data structure.
> >
> > The appending works but I lose all sensor information. (to draw some
> > figures I solved retrieving the sensor information from some previous
data
> objects).
> >
> > I'm just using this data for an ERF analysis, but I'd like to perform
> > also source analysis later.
> >
> >
> > My questions are: how to deal with this issue? Do you think it is
> > reasonable (as I think) to perform an ICA on the overall data even if
> > from different files? Could this issue affect a following source
analysis?
> >
> >
> >
> >
> > Thanks!
> >
> >
> > --
> > Giorgio Arcara
> >
> > Post-doc research fellow
> >
> > Department of Neuroscience, University of Padua Via Giustiniani, 2
> > 35128, Padua, Italy
> >
> > https://sites.google.com/site/giorgioarcara/
> >
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