[FieldTrip] Extracting a timecourse from cluster of channels

[Eric Maris]

Hi Clara,


> Do you think it's reasonable to take the intersection, or union, of
> channels over time in a given space-time cluster?
> Do you know of any publications that have dealt with this issue
> (choosing channels from a space-time cluster for timecourse
> extraction) that I could look at & reference?

I wish I could, but I cannot help you here. Your question belongs to the
category "important but not answerable on a principled basis (at least for
me)".

Best,

Eric Maris

 



> Thanks, Clara
> 
> On Sat, Jul 30, 2011 at 9:31 AM, Eric Maris <e.maris at donders.ru.nl> wrote:
> > Dear Clara,
> >
> >> I am using fieldtrip's cluster-based permutation test to identify a
> >> significant channel-time cluster showing an effect.  Now I would like
> >> to extract a timecourse averaged over these channels (for the purpose
> >> of comparing different conditions, not used to generate the cluster),
> >> but I'm not sure if it makes sense to do so because the channels
> >> belonging to the cluster change over time -- would the timecourse have
> >> contributions from different channels at different time points?  Do I
> >> need to limit my cluster to fixed channels across time? (And if so,
> >> how do I do that?)
> >
> > Yes, you should fix channels across time. The most important point in
> > selecting the channels is finding evidence for the fact that the
channels
> > reflects a single source only. This is not a statistical issue, and
> > therefore there is not a p-value that can guide you in this choice. If
you
> > have collected MEG data, the best evidence is a dipolar topography of
your
> > effect.
> >
> > Best,
> >
> > Eric Maris
> >
> >
> >>
> >> Thanks!
> >> Clara
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> 
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