[FieldTrip] dimord single-trial source data

[Stephen Whitmarsh]

Hi Jan-Mathijs,

Thanks. In fact, I did what you suggest, but this entails a lot (nr. of
positions) or creating and clearing a temporary variable. For a reason I do
not understand (but which I encountered before), MATLAB seems not able to
deal with this, and runs into memory problems. I suspect it is not able to
create and clear many variables in a row, so that althought memory load
does not seem to increase, it *will *break with an out-of-memory problem. I
therefor started with this approach, but alas, I now understand that it was
a wrong turn.

So, I am in a pickle now, as neither option works...

Best,
Stephen

On 16 November 2017 at 14:31, Schoffelen, J.M. (Jan Mathijs) <
jan.schoffelen at donders.ru.nl> wrote:

> Hi Stephen,
>
> I think that it is currently not possible to pass the output of
> ft_sourceanalysis to ft_freqanalysis directly, since ft_freqanalysis
> expects channel-level type data in the input.
> The exact details of the computation depend a bit on the amount of RAM you
> have, and on what exactly you want to achieve.
>
> If it’s your intention to generate frequency spectra for many dipole
> locations (e.g. >1000 or so) I would consider the following:
>
> - compute spatial filters (cfg.keepfilter = ‘yes’);
> - use a for-loop across (chunks of) dipole locations to create ‘virtual
> channel data’, by premultiplying the sensor-level data.trial (loop across
> trials) with the location specific spatial filter.
> - stuff all this into a data-structure that looks like a raw data
> structure;
> - pass this to ft_freqanalysis
>
>
> Alternatively, you could consider using a parcellation approach, if you
> think it makes sense to reduce the number of spatial locations a bit,
> although theoretically it should be possible to create a parcellation that
> consists of just a single dipole per parcel. In this context, you could
> look into the inner workings of ft_sourceparcellate, which returns a data
> structure that ft_freqanalysis can work with. Whether ft_sourceparcellate
> can swallow single trial source data, I am not sure.
>
> Best wishes,
>
> JM
>
>
>
> > On 16 Nov 2017, at 12:36, Stephen Whitmarsh <stephen.whitmarsh at gmail.com>
> wrote:
> >
> > Hi FieldTrippers,
> >
> > I was wondering is there is a recommend/most consistent way to represent
> trial x pos x time data from an LCMV beamformer, also considering the
> dimord. In other words:
> >
> > with:
> >
> > data.method = 'singletrial'
> >
> > should I use:
> >
> > data.trial{pos} = [rpt x time]
> > data.dimord = '{pos}_rpt_time'
> >
> > or rather:
> >
> > data.trial = {pos x rpt x time}
> > data.dimord = 'pos_rpt_time'
> >
> > or something else? The purpose is to then do a frequency analysis (with
> keeptrials = 'yes').
> >
> > Best,
> > Stephen
> >
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>
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