[FieldTrip] Beamformer confusion

[Eelke Spaak]

Hi Tyler,

You write that you end up with the same result "whatever data you
process", so I suspect the raw EEG/MEG data is not to blame.

Rather, I suspect something is wrong with your leadfield or one of its
ingredients: the volume conductor model, source model, or
electrode/gradiometer definitions. It's probably a good idea to check
whether these three ingredients all line up. Could you plot them in
one set of axes, as described at the end of this section:
http://fieldtrip.fcdonders.nl/tutorial/beamformingextended#computing_the_sourcemodel
?

Best,
Eelke

On 26 June 2014 10:00, Tyler Grummett <tyler.grummett at flinders.edu.au> wrote:
> Hello Fieldtrip,
>
>
> I have been using the LCMV beamformer in fieldtrip for some time now, so I
> have experience with it.
>
>
> I am facing an issue where whatever data I process I get an image identical
> to attachment 'sourceplot.png'. We have tried visual SSR, memory tasks,
> tactile tasks etc.
>
> Also, whatever I do with the data, the same issue occurs (filtering etc).
>
>
> Attachment 'original_data.png' shows the data before going into the
> beamformer, and 'virtual_data.png' shows the data after it has run through
> beamformer.
>
>
> We have tried filtering in every possible combination ie lowpass = 40/30/20,
> highpass = 1/10/20, we even did a highpass of 100 and it
>
> was still identical.
>
>
> We dont think this is a fault of the beamformer, but we cant work out how to
> get rid of the issue. It is overpowering the other data.
>
>
> We have also had a look at some spectra of the brain region with the high
> power and a brain region that doesnt have the high power and it appears
>
> as though there is higher power over all frequencies.
>
>
> Before asking:
>
> -There isnt any muscle, the data was recorded from a paralysed person.
>
> -We have tried it on CAR'd data and data that hasnt been CAR'd
>
>
> We are all out of ideas.
>
>
> Kind regards,
>
>
> Tyler
>
>
> *************************
>
> Tyler Grummett ( BBSc, BSc(Hons I))
> PhD Candidate
> Brain Signals Laboratory
> Flinders University
> Rm 5A301
> Ext 66124
>
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