[FieldTrip] Appending data from two sessions for ICA

Eelke Spaak eelke.spaak at donders.ru.nl
Wed Feb 11 12:16:37 CET 2015

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.


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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