[FieldTrip] What does cfg.lcmv.fixedori = 'yes' mean?

[Britta Westner]

Hi Lin,

cfg.lcmv.fixedori = 'yes' will compute a so-called scalar beamformer, and
the spatial filter has indeed just one orientation represented per source
point. This orientation is an optimal orientation that maximizes output
power and is determined using an SVD. This orientation however does not
vary over time, but will vary from source point to source point (and will
depend on the data covariance matrix).

Hope this makes things clearer,
Britta



On Thu, Jun 10, 2021 at 8:52 PM Lin Wang via fieldtrip <
fieldtrip at science.ru.nl> wrote:

> Dear fieldtrip experts,
>
>
>
> When using LCMV to conduct source localization, I'm wondering what
> cfg.lcmv.fixedori = 'yes' means here.
>
>
> According to this tutorial
> <https://www.fieldtriptoolbox.org/workshop/paris2019/handson_sourceanalysis/>,
> it says that "we specify the spatial filter to have a ‘fixedori’, which
> means that for each dipole location the source is assumed to have a fixed
> orientation". This seems to suggest that the defined dipole has only one
> orientation and is fixed over time.
>
>
> However, another tutorial
> <https://www.fieldtriptoolbox.org/tutorial/beamformer_lcmv/> commented:
> "cfg.lcmv.fixedori = 'yes' % project on axis of most variance using SVD".
> This seems to suggest that the defined dipole can have a free orientation
> that varies at different time points.
>
>
>
> Or am I misunderstanding anything here?
>
>
>
> Thank you very much for any explanation/clarification.
>
>
> Best,
>
> Lin
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> https://doi.org/10.1371/journal.pcbi.1002202
>
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